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High Performance Space Conditioning Systems: Part I
October 21, 2014
Andrew Poerschke, Research Initiatives Specialist, IBACOS
Kohta Ueno, Senior Associate, Building Science Corporation
Gail: Hello everyone. I am Gail Werren with the National Renewable Energy Laboratory. And I’d like to welcome you to today’s webinar hosted by the Building America Program. We are excited to have Andrew Poerschke and Kohta Ueno joining us today to talk about strategies to improve the performance of heating, ventilating and air conditioning systems for low load homes and home performance retrofits. Larry Brand of the PARR team was unable to join us today. Before we begin, I will quickly go over some of the webinar features. For audio, you have two options. You may either listen through your computer or telephone. If you choose to listen through your computer, please select the mic and speaker’s option in the audio pane. By doing so, we will eliminate the possibility of feedback and echo. If you select the telephone option, a box on the right side will display this telephone number and audio pin you should use to dial in. Panelists, we ask that you please mute your audio device while you are not presenting. If you have technical difficulties with the webinar, you may contact the GoToWebinar’s helpdesk at 888-259-3826 for assistance.
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Today’s webinar is being recorded and the recording will be available on the DOE YouTube channel within a few weeks. We have an exciting agenda prepared for you today that will focus on strategies to improve the performance of HVAC systems for low load new homes and home performance retrofits. Before our speakers begin, I will provide a short overview of the Building America Program> Following the presentations, we will have a question and answer session, closing remarks and a brief survey.
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And now, onto today’s presentation. Our webinar today will focus on strategies to improve the performance of HVAC systems for low load new homes and home performance retrofits. If you would like more detailed information about any of these efforts or if you are interested in collaborating, please feel free to contact any of our presenters.
Our first speaker today is Andrew Poerschke. A research initiative specialist at IBACOS. Andrew uses his expertise in sensors and monitoring hardware to design and implement remote data acquisition system to monitor test buildings and analyze the performance of HVAC system to calibrate transient thermal models. His work at IBACOS also includes new product innovation, testing products for manufacturers and evaluating new systems against established metrics. Andrew’s presentation today poses a question of, what is simple when it comes to space conditioning? He will reveal alternatives to centrally ducted furnaces, distribution to each room, discuss how these options maintain comfort and explain topics to talk over with clients looking for simple and low-cost alternatives to a single furnace and duct to each room.
Next up is Kohta Ueno, a senior associate at Building Science Corporation. At BSC, he conducts forensic field investigations, energy and hygrothermal modeling, building science research and field testing. Today, Kohta will discuss BSC’s research on ductless heat pumps versus mini-splits in high performance houses, often configured as a simplified distribution system needing one heat source per floor. BSC monitored eight of these houses in Massachusetts from 2011 through 2014, and Kohta will present analysis of the monitored data. With that, I’d like to welcome Andrew to start the presentation.
Andrew: Hi. Thank you. I hope you all can hear me. And thank you again for your time today. Let’s get started. So a brief overview of what I’ll be talking about today. We’ll start by, I guess, defining the problem and the challenges that we’re facing with low load homes and space conditioning. We’ll talk a little bit about thermal comfort and then we’ll get into some of the solutions that we’ve investigated and talk about data from two case studies that we have a cold climate unoccupied lab house and a hot climate occupied test house.
So, some of you may have seen this picture before. We’ve talked about you know, as we’re moving loads lower and lower in production homes you know, the size of that load is reducing. But what isn’t reducing is the overall square footage of these homes. So we see a house which built to benchmark standards might have been a 7-ton cooling load. In the new house is now 3-ton cooling load. And what’s important is that the total CFM you know, has been reduced significantly but the square footage hasn’t. We’ve gone from 2800 CFM in this benchmark, old construction style down to just 1200 CFM but we still have to condition, you know, this very large house. And that presents a lot of challenges you know, a lot of homes are built with floor plans which you know, have a lot of rooms which are disjointed from the center of the house and it can be pretty significant challenge to condition all of those rooms. And so, traditional air handlers you know, might not be the best solution anymore to continue in to condition this low load homes.
So a little bit about comfort. The definition for comfort is probably best stated in ASHRAE Standard 55 and there’s a lot of technical details that go into defining comfort. But ultimately what it comes down to is that it’s a subjective evaluation. That it’s, you know, expressed as an individual satisfaction with the environment. And so it becomes, you know, as much as we like to define it in scientific terms it can still be very difficult to define comfort. And so what we like to use often is ACCA manual RS as a rough guideline for establishing comfort and the definition is that all of the rooms should be 2°F of the thermostat during the heating season and 3°F during the cooling season. And to that sense, a home owner can set their thermostat to whatever they feel is comfortable and they should expect the entire house to have a uniform level of comfort.
So let’s talk a little bit about system design and some of the challenges that are currently being faced by low load homes. Something that’s very significant that’s becomes more and more prevalent as the overall show and enclosure load that goes down is the disparity between heating and cooling modes. And the amount of air flow that’s needed to satisfy that load, you know. In modern forced air systems, all of the load is satisfied by moving air from either a hot point or a cold point and moving it all over the rooms within the house. So there’s a lot of numbers on this chart but I just like to point out that the difference between heating air flow and cooling air flow can be pretty significant. Sometimes it’s half the value of one or the other. And so as a designer people are often faced with the question, which air flow do you deliver? If you deliver say, the greater amount of air flow during one season, you might under-condition or over-condition that space during the other season. So there’s a challenge here that doesn’t have a direct answer.
But we’ll try to discuss some of the ways around that, you know. And so, the other challenge that we’re faced with, with lower and lower air flows is mixing the air both in the zone and around the house. And here is just a little bit of CFD modeling we’ve done. And in the standard registered case, you can see that there is some mixing but what actually is happening here is you have a lot more stratification. And we’ve actually looked at a case with a much smaller register that results in a higher outlet velocity and you can actually see that there is somewhat better mixing down into the room in that case. So the same CFM but you get better mixing. So you have to be very careful with your design in order to mix the space.
And similar behavior has seen in the cooling mode where we have, you know, again, a little bit more stratification with the standard register, the air just kind of spills out whereas with a little bit of a higher velocity you actually mix that room better. And that something that, you know, a strategy we’d like to suggest when it comes to lower and lower loads, you know. But, you know, it’s not all that easy because you do still have to be aware of the occupied zone and diffuser placement is crucial. You can't have these increased velocities in the occupied zone or, you might end up with complaints about drafts.
So diffuser placement is also very critical if you're using these systems. Some of the challenges that were currently seeing lower and lower loads have resulted in lower CFMs and potentially lower system runtime if the system is oversized. That reduced CFM means less velocity and throw and in turn, that results in less mixing both within a room and within the whole house. So we have a challenge here to continue to provide adequate comfort with working with a lot less air and then also, on top of that this load disparity is between the winter and the summer also require a better mixing in longer system runtime in order to adequately condition those exterior rooms that could potentially be sun tempered.
And we’ll see this issue coming up in some of the data that we’ll look at. And so, different CFM between summer and winter presents some challenge, you know. So, what are some solutions, what should we be thinking about? You know, again, as always, equipment selection is critical. And, you know, total CFM is also critical. And you have to understand the impact that will have on mixing in the entire house. And so if you do use ducts you know, it’s necessary to design that correctly to get the CFM that you need in each outlet. And once that system is being designed and installed you know, it’s really necessary to verify if that is correct that you’re getting your acquired CFM or else there’s gonna be problems with comfort.
You know, in something that we’re finding more and more provides a good alternative is to look at this higher velocity systems and to design your system to maintain something like, you know, 600 feet per minute out of the register in order to adequately mix that room, to get adequate throw and, you know, along that line, it’s also necessary to think about the register, to think about the outlet and pick one which will provide adequate throw and mixing. You can’t just use, you know, one register for the entire house, whatever is available. You really have to select that and change that depending on your CFM.
And now, let’s talk about the simplified systems that we’re throwing in to the mix here. You know, are we talking about simple ducts? Are we talking about no ducts at all, simple controls, maybe a simple air handler? Let’s look at a couple of the simplified systems we’ve studied. So one case is to use a limited number of duct runs, perhaps you know, just duct runs to the bedrooms with essential air distribution system, taking a traditional system and, you know, scaling it back as much as possible. That’s one thing we’ll look at. You know, another case might be a single point of distribution with passive transfer to all of the rooms. If you have a single-story house you might think about supplying all of the air to one central room and you know, if the house has a low enough load, you might actually keep all of the rooms comfortable by using one outlet.
And if that’s not sufficient, you know, something else that we’ve looked at then, is using active transfer fans between the zones. So if you have a number of bedrooms which are, you know, distant from the central air handler we’ve looked at the effect of active transfer fans which are forcing air to mix zone to zone. Again, that’s crucial as mixing air not only in a room but from one room to another.
And one of the strategies we’ll look at a little bit is mini-split heat pumps, and a case study in a hot climate where we used some mini-split heat pumps. All right. So the first case study we’ll look at is the lab house that we have conducted research on for a number of years in Pittsburgh. This is a cold climate and the house is constructed to a very high efficiency standard. You know, it’s not quite passive house. But it is a very low air change per minute, 0.6 with very high levels of insulation in the exterior and the attic. So we’ve studied a number of different strategies in this house over the years and we’ll present, you know, some of the results from these different studies. I’ll briefly mention them now and then go into a little more detail as we continue to talk.
So, we did a single point distribution strategy with two thermostats and just two zones and the one outlet was located in the first floor, one outlet in the second floor. We also did a single point distribution strategy, the same set up with two outlets, one on the first floor and one on the second floor. And we looked at the impact of active transfer fans to try to improve some of the mixing between the zones. And finally, for this case study, we’ll look at a scenario where we try to limit the number of ducts as much as possible in order to try to maintain comfort with the simplified system.
So the first strategy we employed was the single point distribution with passive mixing between all of the zones. Now right here, we have a floor plan of the first floor of the test house. And you can see the supply register was located in one room and the return was located in another. Now, the first floor of this house had no real doors for the major zones and so, it’s a rather open floor plan and so it’s rather effective at mixing air throughout that entire zone.
So here is some data from that case. I’m just gonna take a minute and try to explain this graphic a little bit. On the left side here, we have the temperature in the zone relative to the thermostat. And we’ve marked the comfort band that we used plus or minus 2°F which is this gray band and all of the rooms then are plotted and you will see sometimes they stay within that band and sometimes they go beyond that comfort band. But this is the temperature of the room relative to the thermostat.
And for context, we’ve also included the outdoor temperature and the temperature at the thermostat. You can see on this day, it was a cloudy day, and the temperature was around 20°F. And so one of the things that we were studying during this case is the effect of a deep setback. If the homeowner had turn the thermostat back overnight and then, turned it on and we wanted to look at the impact of the response that morning, so you can see the system did not operate overnight and then kick on in the morning and some of the rooms became uncomfortable. And that’s the result of that setback. However, throughout the remainder of the day, once it returned to steady state, the zones did fall back down into the comfort band and that whole first floor was comfortable, supplied by a single outlet for all of the conditioning air. So, you know, that setback response is still something, you know, of a challenge, however, this does work for open floor plans.
Now, let’s look at the second floor. We had a single outlet in the second floor which is supplying all of the conditioning air into the central hallway which is in blue. And then we looked at different cases. One case, we had the doors open and we looked at the passive transfer into the rooms and we looked at the impact that had on comfort. Then we looked at another case, where we closed the doors and installed and ran this active transfer drills and looked at the impact of mixing in that case, to see if it could maintain comfort.
So the first case we’re going to look at is a sunny day on the second floor with the doors open. And again, we’re looking at the house returning from a very deep setback. So you see the room temperatures are well below the thermostat design temperature. And then, what we have is once the system begins to operate, those temperatures, you know, they elevate and then they tend to go beyond what the thermostat is calling for. And so, we’re actually seeing with doors open, a lot of the air mixing into some of the rooms and not as well into the other rooms. We have this pretty big disparity.
So, it started to work but the strategy still didn’t provide what we felt to be adequate comfort. So we looked at another case, where the doors were closed. And we looked and we used the active transfer fans to try to mix those rooms. And again, this is a single outlet on that second floor hallway and we have these four bedrooms that we’re looking at the impact of the comfort. And so, what we’ll see here is that one of the bedrooms did tend to run a little bit colder than the rest. So that bedroom would be considered uncomfortable. However, the rest of the rooms did more or less stay within that boundary. So, in this case, you know, we gotta say that it didn’t meet the standard but potentially you know, that could be increased CFM or something that would help this one bedroom maintain comfort. But again, the challenge that we continue to see here is that, if you're not supplying conditioned air to individual rooms you know, we tended to see those rooms not maintaining comfort.
So let’s look at a different case. That was a cold cloudy day. Now let’s look at a cold sunny day. And what we see is the rooms which have a lot of southern glazing tended to overheat during the day. They weren’t mixed well enough with the rest of the house and so that solar heat can present in some challenges. Now, these were unshaded windows so it’s possible that with, you know, using some shading devices, you may be able to maintain comfort in this case.
So, another case that we then looked at was to supply a very limited CFM to each of the rooms on more of a consistent basis and see if that in effect, could condition the rooms without, you know, a full duct system. In this case, we used some very small diameter, two inch pipe to deliver that air. And despite that continuous operation, we still saw problems during cold sunny days with overheating. That it just wasn’t mixing well enough. So this continues to be a problem that we’re seeing is houses that have a lot of glazing tends to overheat. And so there’s different strategies you might be able to use, such as, you know, shading that would help reduced this impact.
And so then, as a reference point, we also looked at a case with a right size system supplying air to every room to see, you know, if that worked. We looked at this simplified cases and, you know, sometimes it does work, sometimes it doesn’t and we want to see now the impact of a traditional system. So this is the second floor, door is closed and we see this similar problem where on a sunny day, we have overheating in the sun-tempered bedrooms that don’t have a thermostat in them and they're not thermally connected to the rest of the house very well because the doors are closed. You know, and during that period, the system did not run at all because the thermostat was satisfied but we didn’t have mixing through this period.
And so, some things that impact these are the conduction between different rooms potentially, you know, if there are ways to improve the conduction between rooms, that could help mitigate this problem, you know. A lot of the results were heavily impacted by the location of that supply register and that single point of distribution, if it was blowing them to one of these rooms, that room could potentially overheat or be under cooled while the other rooms were not. And the other most significant driver in this house was the impact of solar heat gains, so the front of the house faced due south. So the bedroom in the bottom corner saw the most significant impact of the solar heat gains as well as this western bedroom. As we saw, those rooms tended to overheat when the rest of the house stayed comfortable. So the challenge still is you have to mix the whole house if you want to maintain comfort.
So let’s look at a little bit of hot weather in data. So again, now, we’re back to the first floor, this is the open floor plan. And we had that single point of distribution centrally on that first floor. And again, let’s focus on the comfort band which is this gray band here. We see that all of the room temperatures stay within that boundary during this period and even during the period of pretty extensive system runtime. So, you know, this works again quite well even in the summer for an open floor plan.
Now, let’s look at the second floor. Whenever there’s no sun tempering, those rooms do stay within that comfort band. But as soon as we see the impact of the solar heat gain again, we’re seeing this overheating even in the summer.
And so, let’s look then at the right size system during the summer. Here on the first floor, it did maintain pretty adequate comfort. But again, on the second floor, even the right size system struggled to keep up with this solar heat gains and the system is running through this period but there’s not adequate mixing through those rooms. And that is key. In order to maintain comfort in those rooms you really need adequate mixing.
So, let’s move on now to the other case study we’re going to talk about. We have a hot humid climate and an occupied test house. This house is built to zero energy ready home specifications. And with a conditioning strategy that we implemented was to use a combination of ductless and ducted mini-split heat pumps. So the floor plan of this house was in a five-bedroom home, so we have a number of rooms that were disjointed from the center of the house and so as a result, we used a number of heat pump units.
On the second floor, we had one ducted unit which supplied several of the bedrooms and two ductless units; one for the central game room and one for a guest’s suite. And what we’ll see here is that in the guest’s suite we’re able to actually turn off or turn on that zone depending on its occupancy and see energy savings because of that.
On the first floor, we had a central unit which supplied the main living spaces. This is again a ductless head unit. And then another ductless unit in the front area. The master suite was located on the first floor and kind of central in the house and it had a ducted unit to supply the couple of rooms in that suite.
So this is some preliminary data from this year that we’ve been collecting on an ongoing basis and we’d like to share some of these preliminary results with you. During the winter, in this house it was actually unoccupied at this point. And however, the systems were on and running so we have some data that we can start to draw some conclusions. And so, what you see here is actually the guest’s suite which was set to a different temperature. And it is you know, so that’s why we set this elevated temperature.
Now, the rest of the rooms did maintain a pretty tight grouping within their zone. So, we have, you know, something on the order of a 4 degree temperature difference between the hottest and coldest room. However, the individual zones did maintain a very tight temperature clumping during this period. Now, it’s unoccupied, the doors were open but it did seem to be effective in this case. So now, we have some data from the summer and during this period, the house was occupied. And we’re looking at a number of very hot days here. And so, as I mentioned before, that guest’s suite, you can see is drifting above the rest of the house. During this period, the mini-split heat pump in that room was turned off. So the occupants were able to have complete control over those rooms. And then looking at the rest of the data, we see other rooms which were on similar setpoints we see them very close together. They were well within that three degree temperature band if you look at the individual rooms which were on different setpoints.
So the strategy seems to be quite effective in this case. So, some of the conclusions that we can draw here are that large open spaces can be effectively conditioned from this simplified systems. But it’s crucial that you have the correct placement and you know, the correct register selection for that single point of distribution. Is it ready for every house out there? Certainly not. And that’s something that we found through this testing and we found some potential ways to help improve those cases when it did not work correctly.
Now, something else that we found is that setup and setback can be hard to do uniformly. If you have a period where, say, the occupant is on vacation and they’ve turn off the system and all of the rooms in the house have been able to drift apart, whenever that system kicks back on it’s difficult to get it, all of the rooms, back into a uniform temperature through that operation. And it’s, you know, the biggest challenge still is conditioning the furthest rooms from the setpoint or from the thermostat and they still need direct conditioned air. It’s not adequate enough to have some of this passive mechanism to condition those rooms. If you want to maintain and guarantee comfort you still have to condition some rooms but then use simplified things in other rooms.
And something that we’ve found and will be discussed in much greater detail in the next presentation is that, mini-split heat pumps, both ducted and ductless using the combination of those, offer a very compelling alternative to the traditionally ducted systems. And they also provide the homeowner with the greater level of control over the specific setpoint and this specific operation.
So that’s it. My email is here. We’d like to acknowledge S&A Homes and Imagine Homes. S&A Homes was the builder of the Pittsburgh lab house and Imagine Homes for the hot and humid climate test house. I’ve also got links to some of the reports which we’ve written on these homes if you have further questions
Gail: Thank you, Andrew. Next up is Kohta Ueno.
Kohta: Am I unmuted? Okay. I’m unmute now. Okay. This is Kohta Ueno. We’re going to be doing a presentation on the research that we did on the mini-split heat pumps operating in heating and cooling mode in a bunch of houses located in Northeast in Massachusetts. So just jumping into my presentation here. We’ll do a little bit of background. So, we spent a lot of time working with a builder known as Transformations, Inc. Their shtick is they have been building net-zero houses throughout Massachusetts and they're working on a variety of configurations. They’ve been doing this as their production basis housing for a bunch of years at this point. Part of their mix of strategies is to use this mini split heat pumps, this non-ducted heads mounted on walls as part of their tradeoff packages of doing more investment in the building shell or enclosure and then using a simpler or lower cost base conditioning system. What they have been doing is they’ve put a single point of heating or cooling on each floor, typically, on a two-story house. And the study examined the temperatures throughout the house, throughout a variety of operating conditions and the energy use of this mini split heat pumps.
So, just take a quick step back. This is only the half hour presentation version of this gigantic, 140 page report that we all suffered through here. So this presentation is an overview, you know. The report has all the details. It’s currently in final review and it will be released very shortly. So, please, if you are, you know, frantically taking notes and screen shots, you know, just relax, sit back and watch the screen and just listen to the work, please.
So the type of enclosure or shell that Transformation uses is shown in some of these figures. The walls are double stud, 12 inches thick, with 12 inches of low density open cell spray foam. The roof is well air sealed and then a vented attic with foot and a half of cellulose, you know, R60, well north of R60. Going down to the basement, close cell foam, typical application on the walls, R20-ish and [inaudible] [00:37:36] foam underneath the slab. The standard product uses triple glazed windows, in the 0.2 range and they're hitting 1 ACH 50 typically.
So, a bit more about mini split heat pumps. This type of product has been available and been in use in Asia and Europe for over 40 years. It’s a very common technology. And since coming to North America, it’s just getting greater and greater acceptances in the market place. Now, one warning about mini split heat pumps if you're comparing them with the standard ductless split system, the equipment is more expensive on a per ton basis, you know, per, you know, 12,000 BTUs. But, you know, if we’re talking about replacing a ducted system with a ductless system, you can actually gain significant savings because a lot of the installed cost of the split system is the, you know, the sheet metal or the distributing system. In this study, we used equipment from Mitsubishi. There are a couple of other manufacturers that have some fantastic low-temperature performance which is critical if we’re talking about relying on this heat pump as the sole source of heating in a cooling climate like Zone 5, Massachusetts. So they retain their full heating capacity at outdoor temperature -5 degrees. They’re rated down to -13 and some other practitioners that I have met have had them operating down to -20. And know, this is a specific type of equipment from certain manufacturer. Other manufacturers do have equipment that can run down to this level.
Another nice thing about mini splits is that they modulate to meet load. Basically, they ramp their fan speeds and compressor speeds up and down based on how much load they’re facing with what the outdoor conditions and indoor conditions are. One thing that’s found if you’ll look at the ratings is that the best performance you can get out of these units is at part load. And they are the worst at full load. Basically, if they're chugging along at full load, they're at their lowest efficiency point. But, you know, that being said, several practitioners have examined this problem and in cold winter conditions, they were showing COPs or Coefficient of Performance in the two and a half to three range. It was just actually excellent for a heat pump. COP, of course, is the ratio of how much energy out of the heat pump you get versus the amount of energy you're putting in using electricity.
So, the builder’s experience with this mini split heat pumps. Transformations build very low load houses in the 10 to 18,000 BTU/hour, heating design mode range. So this is below low, what even the smallest furnaces out there are, you know, the smallest furnaces I’ve seen are 40,000, maybe they modulate down to 30,000. All of their production uses these mini split heat pumps as the single source heating with no backup. Typically, one per floor so two for a 1800 square foot, two-story house.
So, like I said before, he’s taking the savings from the mechanicals and putting it back into the enclosure. So, just as a ball park cost, the cost of all those enclosure upgrades that I’ve mentioned for, probably about $15,000 for a standard size house and about $5,000 in savings on using this type of a simplified mechanical system. And what the builders’ experience have been so far is that, you know, very trouble-free operation. It’s very reliable, very few callbacks. And when he has had a callback, it’s typically something incredibly dumb like the HVAC installer forgot to completely plumb the line or something like that.
By the way point of information, you're looking at that lower left hand image you will notice that the mini split head is mounted on a small sheet of drywall. This is actually done so that the installer who’d come and installed all of the equipment in a single shot just would one trip to the job site and then later on, they finish the electrical, other mechanicals and then, you know, insulate in drywall, around that.
So, an overview of this monitoring project. The bulk of the projects, the house that we looked at are these eight houses located in two subdivisions in Massachusetts. There was a mix of monitoring packages in each of them. Some of them had, you know, temperature or a sensor throughout, other of them have, you know, also added sensors that would tell the status of the door, open or closed, which actually has significant effect on this type of simplified space conditioning problem as well as power use of the mini splits. You can see that these houses were monitored over various periods of time. Some of them, you know, much less data. And the others, longest one was well over two years. The shortest one was a little, sort of, few were a little bit under a year. And you can also see that we went through some, you know, both mild winters as well as some pretty severe winters, you know, well north of the standard type of winters you would see.
Just showing some pictures of the monitoring packages. We would mount temperature relative humidity sensors on the walls in couple of locations throughout the house. The mini split heat pump energy use on a five-minute basis from the power panel and the door open and close status would be done with a small data logger that has a read switch of that text proximity to a magnet mounted on the doorframe. And so you could tell if the door was closed. Unfortunately, the system does not actually tell you whether the door is fully closed or partially closed, should we close or--well, it does not give you, you know, give you indication of how close the door is. It only gives you an open or closed. So it’s entirely possible that the open signals are also partially closed.
This shows an image of what a typical monitoring package setup might look like. This shows one of the smaller houses, the attached garage in first floor, showing the mini split heat pump over in the living room, the large space, flowing into that space and there are two temperature relative humidity sensors shown by these two green dots, in two locations on the first floor. On the second floor, there are almost similarly to temperature RH sensors as well as those door closer sensors on the two bedrooms, the places were doors were expected to be closed for extended periods.
Okay. Well, we’re going to look a little bit at the monitoring data that we had. And the first thing I’m gonna do is just little bit of an overview of the type of operating patterns we saw in the data just so you have an understanding of, this is the type of data that we collected and this is the kind of thing that we can learn out of it. So this shows a typical plot that I use to show temperature and power use in these houses. So the orange is outdoor temperature. This is a chunk of winter from November through May. And the remaining traces are indoor temperatures. You can see they all fall within the pre-narrow band and most of them in the 65 to 70 range, some excursions but they're mostly cracking together, the most part. But the other thing that we did monitor was the mini split heat pump energy use. So what those blue dot show, are the hourly energy use for the mini split heat pump that is graphed on the right hand side, shows, you know, this is a thousand watts in average draw per hour, 2,000 watts for 1 hour.
And what you can glean out of this is you can see towards the beginning of the winter, you know, then this got colder and colder, they realized, “Ha, I guess, it’s time to turn on the heating system, eh?” So you can see that they slammed the heating system in here and run for a bunch of hours at pretty high load. The maximum load for this system is about 2,000 watts. And you can see that it just kind of chugs on, very few hours at zero which just, kind of, modulates up and down based on outdoor temperature how hard it is running. So you can see at these various points where it gets mostly colder that you have a fair amount more electrical draw from your mini split heat pump.
So the blue data was for the first floor unit, the red data over here shows the second floor unit. You can see that it runs a little bit less but a similar type of patterns running, you know, cycling up and down. So if you also looked at the five-minute data. You can determine that this equipment actually is definitely modulating. You know, very few hours running at zero, it is not, you know, slammed into gear and then shut off. It just ramps up and down based on the temperature. And also that comparison between the first and second floor, you can see that the first floor is really doing the heavy lifting on the heating side.
Moving on to a plot of the cooling side, you can see a similar type of behavior where, for instance, over here, you know, we had a couple of hot days. They realized it’s time to turn on the air conditioner and they turned on both units, most of the indoor rooms are tracking pretty close to each other. The second floor is doing most of the cooling. And you can see this one point, they probably just turned down the second point of the first floor unit perhaps and then they all kind of came into line or they probably turn down the setpoint on both and they all just came in the line after that.
So, one of the questions you want to ask is, you know, people do not trust heat pumps in a cold climate to heat a house. So let’s look at equipment capacity. Did it actually need setpoints and not have any comfort complaints on that front? So, like we said, we’re using these heat pumps as a single source of heating the Massachusetts’ Zone 5A. Those two sites had these odd temperatures of plus or minus two Fahrenheit. The NREL testing that they did back in 2011 showed that the published specifications from the manufacturer are actually pretty reasonable. They do match outputs at those whole temperatures like they claimed in their literature.
So, in the monitored data, there was no sign of low equipment capacity problems. That would be, typically, demonstrated by having a really long runtime at maximum capacity and the indoor temperature has fallen during cold temperatures. And there was no sign that I saw in any of this those types of problems. There were very often loads of excess capacity available, you know, well below the 2000 watt draw point. This included the winter of 2013, 2014, the so-called Polar Vortex with way higher heating days than a typical winter day in that climate.
On those times when we saw temperatures declining indoors, it was typically because they either have units set at a low setpoint or they just have it on plain old off for some reason or some other malfunction or other control issue.
And that being said, you know, one of the things that I’ll, you know, we have to put is, what was the sizing of this equipment relative to the design load? So this table I have here are the heating design loads for these various houses, the installed equipment capacity and some of these are in brackets. So those are houses where, they was first with one head installed typically and then there was the second one retrofitted afterwards, down the road. I’ll talk a bit more about that later. And this shows the oversizing factor. So this shows that for most of these houses where the 150 to 200% oversized range and in these houses, after the retrofit in the 200% oversized range.
So this is typically crazy oversizing or most conventional split systems or other units. But one of the things will point out is that, oversizing provide loads of heat capacity at low ambient temperatures as well as the fact that oversizing is not as big of a concern when we’re talking about this mini split heat pumps. Remember, they modulate well over their capacity range. So even though the maximum capacity is well oversized, this can ramp down much closer to the actual loads.
So, you know, the next topic we’ll talk about is what Andrew talked about in great detail, was trying to space condition the two-story house from, you know, one or two point of space conditioning. So just as little bit of background to reiterate what Andrew said. The idea of this is that we’re taking advantage of a really low load home, a super insulated house to simplify out a space conditioning system. The concept behind it is that, because the outside shell lets heat out so slowly. You can think of the heat coming from the core and kind of filtering through all those interior partitions and floors. So as long as the heat is flowing through those interior partitions and doorways and interior gains as fast as it’s being lost through the exterior shell, you’ll have a reasonable temperature inside that room. But if you, you know, if the rate of heat loss through that exterior shell starts getting higher than what you can push through that interior partition or doorway, temperature starts to go down and you start to have some problems.
Just to briefly summarize some of the previous work, this type of simplified space conditioning works better with smaller homes with a compact floor plan. Bedroom doors have a huge effect with the door open, you often have, you know, fine temperatures but you shut the doors, you start seeing larger temperature differences, colder bedrooms in winter and the last thing is that a constant setpoint is definitely how you would want to run this. The more that you mess with the setpoint, the worse the variation and bedroom temperatures of those other rooms is going to be.
Now, for argument’s sake, you can be completely safe and use that fully ducted system but as Andrew pointed out, you will still see temperature variations away from your setpoint or between the rooms. But it’s, you know, at the very least, it is standard practice so it is defensible in that respect. So, you know, take that as you will. So, we did a similar type of analysis, using ACCA Manual RS, looking at the 4 degree temperature difference. And we just simplified analysis here, we took the highest and lowest temperature in the house, in the various points that we measured, took the difference between those two points and plotted how many hours there were at those various temperatures. And just added up the number of hours. So you can see that where were, you know, air number of hours with, you know, zero to one degree temperature difference between our various measurements. The majority was in the one to two degree range, then two to three and it kind of tails off from there.
Also, this analysis omitted the bonus room and basements just because, the basement, for instance, has no space conditioning in it and it was not intended to be conditioned. The bonus room typically was left as an unfinished room and some homeowners did finish it on their own.
So, what you can do is you can look at this bars and you can also add them up for the percentage of the total. And we can see in this particular case, adding up the zero to one, one to two, two to three, three to four, so that’s the four degree difference. You see that 96% of the hours in this particular house were below that four degree mark.
Right. We have a boat load of data to look at, you know, eight different houses of variety of winter and summer operating conditions, the results varied all over the place. Sometimes we had great results, 80 to 90% of the time within that four degree band. Other ones, a lot worse. A lot more detail in this report but many of these houses were under, you know, under that four degree temperature band. And a couple of houses were not analyzed because they were missing some of their key data.
One interesting thing was that we looked at both the wintertime season performance as well as the summertime season performance. What we saw that, was that, in the summer, when the temperature variation was actually a little less than in the winter. The reason for this is that the temperature difference between indoor and outdoor is a lot lower in the summertime design conditions versus wintertime design conditions. Just think about it. You want in the winter, you know, 70 degrees versus zero degrees, about 70 degree delta T, summertime 70 degrees versus 85, 93, 20 degree delta T. But one thing I have to say is that these rooms, all these houses had relatively low glazing ratios and low solar heat gains with those triple glaze windows. So your mileage will vary depending on which type of setup you have there.
So, that’s very interesting. We have a bunch of cases where this tends to work great. So, my thought though is that we don’t want too much of a problem, we let it work. I think we learn a lot more when we look at-- pushing it until it fails. So that was some of the interesting sub-case studies that we looked at here on, you know, what were cases that did have problems, what caused that problems, how do we solve that problem.
So, one of the problems we had was houses with two stories and one mini split heat pump. So this shows a couple of houses where these are on the smaller end of the production that they put out. You know, in the 1200 to 1500 square foot range. So design loads are nice and small, 10 to 11 kbtu/hour which is well within the design capacity of what this mini split heat pumps can put out even at design conditions.
The other thing that the builder pointed out was, he’s been working with these types of mini splits for a long time. He noticed that during the winter, typically, the second floor unit barely runs. So what he was thinking is, “Look, the one mini split should do it on these houses, let’s go ahead and run it that way. So, good experiment, let’s try it.”
So the equipment was located on the first floor in each of these houses. So this shows some of the temperatures that we were seeing inside the house. Once again, to refresh, orange is outdoor temperature going from May through September. Indoor temperatures are showing here. Red is the first floor. These two blue lines that are overlapping each other are the second floor bedrooms. The green dotted is the stairwell which is kind of halfway between the first floor and the second floor.
So what we’re seeing is that, you know, the second floor temperatures are definitely running well warmer than the first floor. And you can also see that there’s this real spike in outdoor temperature and then the second floor really starts to heat up, you know, well in the 80s and above, even though the first floor is chugging along nicely at below 70 degrees.
Then, you know, so basically, the homeowners complained. We try to tweak a bunch of things but we finally gave up and added a heat pump, a mini split on the second floor and that immediately, see the immediate results. It just pulled the second floor temperature right down to the comfort setpoint. So, you know, one of the things to argue with, what about redistribution fans, what about things like that?
You know, pull the hole there and push it into that bedroom. You know, we actually had one of these redistribution fans and exhaust fan pushing 40 CFM continuously from that first floor into one of the second floor bedrooms. And this actually is the performance that we were seeing. So a redistribution fan can help but there is always so much it can do with that air. So it’s all we can help you in an edge case versus a bad case. So, what this tells me clearly is that, you know, warmer rises, cold air sinks, so, you know, on a, you know, using a single mini split on the first floor, that looks great, warm air rises, heats on the second floor. If you’re doing it during the summertime though, that cool air is just going sit there as along on the first floor, your second floor is going to start to rise like this. So, this shows just a couple of images of how that second floor mini split was retrofitted. You can see the lines that hide on the outside you know, it looks, kinds of, like a rain gutter poking right through to the second floor unit. We’re going to run it inside the wall, inside the garage.
So, this thermal buoyancy thing, warm air arising matters a whole lot for distribution even in very airtight houses. You know, all these houses test out in the 1 ACH 50 range, you know, the previous wisdom has often been, you know, all we know, like, thermal stratification happens because you’re leaking all your hot air out so that’s why the first floor is cold and the second floor is warm.
Well, you know, even at 1 ACH 50, physics does happen and you do end up with warm air arising. So, if you’re trying to do one mini split on two floors, choose heating or cooling and be prepared to, kind of suffer for, you know, during one of those seasons or either that or have a really big redistribution system to shove air all around the house.
So, moving on to another topic. Another place where we saw problems were in a bonus room in one of the houses in East Hampton. So, this shows the comfort complaint house that we were looking at, you can see the south orientation, big solar array on the roof, you know, south face on that. So, you know, this is a bit of background. This builder has been doing super insulated and super airtight houses with the two mini split heads and loads in their houses without complaints. A couple of complaints started to crop up in these several mass houses. This specific house was a custom house plan with a first floor bump out, a little bit more square footage and they actually had the builder finished the bonus room over the garage as part of the initial package.
So, this shows another view of that house. The homeowner said that the downstairs temperatures were pretty darn even and that they ran a constant setpoint on both the first floor and the second floor. So, there was a bedroom in front of the house that generally was the warmest, a few complaints there. The rear bedroom was the colder than that, but the bonus room was actually very noticeably cold, 50 degrees in some of the really cold worse case conditions that they saw with a 70 degree, 68 degree, set point inside. So that shows the footprint of the bonus room.
They also had cases where they accidentally left the garage door open and that bonus room got even colder. Not terribly surprising, just look at the geometry. They also had issues with the whole bedroom door open and close thing. They said that, you know, basically they have, you know, they have very strange schedules, you know, leaving a door open is not really something that will work with their lifestyle.
So the first thought was, you know, is this an air tightness problem? We retested that running at under 1 ACH 50, very nice and airtight. And it’s definitely not a capacity problem. So, that second floor had a 12,000 BTU/hour head, the design load winter conditions of the second floor is about 6,000. So, we’re well oversized in terms of capacity.
What we’re probably facing here is a failure for that heat to get from that core out into the bedrooms. So, let’s take a look at the floor plan and see what we have there. So, this shows the plan of the second floor. The front is down towards the bottom of the house so that shows the location of the mini split in the hallway of the second floor, that shows the front bedroom, you know, where they attached, you know, the bathroom and attached to that suite. The master bedroom suite at the back of the house which had some comfort issues and the bonus room over the garage.
So, one of the things that’s, you know, to back up, it’s kind of obviouswhat’s going on probably to most of you. You know, a bonus room over a garage just seemed very different conditions than a second floor bedroom that’s over a conditioned space. The bonus room has exterior conditions on five of the six sides of the cube, if you will, only one side condition the wall. These second floor bedrooms typically have, you know, condition space below, condition space on the other two wall so they do not have nearly as challenging conditions in terms of, you know, the amount of heat that they are sharing.
Another thing to point out is the ratio of interior to exterior walls. Remember what I was saying before about the rate of heat flowing out of a room versus what’s going through partition walls and doorways. So, you can see the ratio of the indoor walls and the outdoor walls for that front bedroom and versus that back bedroom. If you actually just ballpark out those ratios, it’s like 2:1 versus 4:1. So it’s not very surprising to me that that rear bedroom is slightly colder. You can also see that the rear bedroom has only two, you know, has a little bit more in terms of glazing that will, you know, get some of the morning sun and that south facing sun.
If we want to do this type of analysis in more detail, Robb Aldrich from Steven Winter did a very nice job of making just a spreadsheet of what are the relative heat losses and you can just kind of calculate out to what if scenarios of what, you know, what the temperature will be in the room with these various service areas and U values. You add a transfer fan, how is the temperature change, you open the door, how does the temperature change? It’s a quite elegant tool.
So, this shows a little bit of the monitor data from that comfort complaint house. What I’m showing here is the bedroom temperatures that, you know, the green one is the front bedroom that had few complaints. Blue is the rear bedroom and yellow is the bonus room, orange is the outdoor temperature. And so these dots down here show door closure states. These dots indicate hours when the door was predominantly closed for the bonus room, rear bedroom and front bedroom.
So, we can see from this is that over here, they shut the rear bedroom door for a long period of time and you can start to see the temperature slide down there. They also shut the bonus room door and it also starts dropping like a rock and you can see in this sunny state conditions with the door closed for a long period, outdoor temperatures and the freezing and below range, we’re seeing, you know, 60 degree temperatures in the rear bedroom, 50 degree temperatures in the bonus room, definitely well outside of the comfort range to say the least.
But then, again, that being said, you pop open these doors and all of a sudden, these temperatures pop right back up. And, you know, they’re definitely on the cooler side of where you would want to be, you know, in the lower 60s, mid 60s range, but still you can see what a huge effect door open/close state can have on these on the temperatures in this room. You know, as you can see, many hours of this open door data, many hours within the 4 degree temperature range but, of course, these are warmer temperature conditions above freezing range.
All this being said, one thing that I want to point out is just because we had a comfort complaint in a bonus room does not mean a bonus room always causes a comfort complaint. This shows a different house located in one of the other subdivisions and you can see that the dark blue which is the bonus room is definitely on the cooler side of all these rooms. What you see is pretty darn close to all the other bedrooms. It is not operating nearly in that way colder 50 to 60 degree range that we saw in those worst case scenarios in that comfort complaint house.
Moving on to another topic. I said before that turning the temperature on, you know, setback the temperature down or up or setbacks do not work very well with this type of a simplified system. We actually had a homeowner who did this type of operation in their house so we could actually do comparisons how this house operated versus other houses.
So, first as an example, I’m showing a house that ran the temperature at a constant setpoint, you know, just straight flat out, you know, straight flat temperature. Once again, outdoor temperature in orange, indoor temperatures and mini split energy use. You can see the temperatures are pretty close within a reasonable band and that the mini split is modulating up and down. and that, you know, and that basically, you know, we compare the mini split energy use to the 2000 watt heat load where that, you know, we peak out at about 1,000 watts.
So, you know, there’s no big slug of heat-- oops, and this single point distribution works very well with this constant setpoint. This shows the house where they literally turn the mini split on and off. The temperature swing, you know, between, you know, 60 and 70 plus range for, you know, a lot of these things. The homeowner literally operated this unit saying, “I feel like cold. Are you feeling cold?” You know, you turn the system on, ran it for awhile and then said, “Oh, I’m warm now.” And turned it off. So, you can see this kind of saw tooth behavior at swings and you can also see that there are many hours-- this shows like just a few go up in temperature where it coasted down but there are many hours where we’re running at close to maximum capacity, 2,000 watts. You know, basically, when it slams into here and needs to heat up the house, it’s running like crazy. I’ll jump over this in terms of time but, you know, one of the things I’ll point out is that setbacks are often done usually to save energy, that’s the concept behind that. That being said, you know, if you super insulate a house and make it airtight, you know, the temperature in the house drops very slowly during the off cycle so there’s less benefit from doing a setback.
And in addition, this mini split head heat pumps operate at their worst efficiency stage when they’re trying to recover from a setback and it’s also typically going to be the worst time of day in the morning once it’s very cold. So, you know, let’s take a look at how the results came out. So there are two houses that are comfortable size that constant setpoint house about 1400 kilowatt hours of heating use over winter that on/off house almost double that, 2500, 2600 kilowatt hours for that winter. So this on/off operation house was the worst outlier in terms of energy use per square as well as in comparison with the model 160%.
So just talking through a few less items; actually Gail or Heather, how much time do I have left? I’ll just keep going for a little bit here.
Heather: Yeah. If you can just wrap things up in about two more minutes, that would be great. Thank you.
Kohta: Okay. I’ll just jump to my conclusions here. So actually, two things, so one of the things that you want to point out is we actually did calculate out how many square feet per head we had. This is not mentioned, like, some general guidance sizing information but it’s a work well bit of information to realize. You can see most of these houses were, like, 600 to 800, 900 square feet per head in this comfort complaint houses, we’re in the 1100, 1200, we added that second head, we’re down to the 600 branch per head.
So just a little bit of things to think about when you’re trying to design with a system like this. So, further work that we’re going to do with Transformations, we’d like to possibly implement a different type of system for the second floor. Those comfort complaints at East Hampton and they had to change to 3 to 1 indoor to outdoor mini split system on the second floor. Basically, one head per bedroom to ensure that these comfort complaints would not happen again. They ended up with more costly equipment and its lower efficiency and as a result, they lost a really big energy incentive on each house. So what they’re hoping to do is change to a small ducted air handler in second floor hallway, a short duct run to each bedroom. There, we solve the whole open/door close problem and we’re providing space conditioning to heat the bedroom as result.
This just shows a small image of the type of air handler that we’re talking about. The problem is that this kind of equipment does not quite exist yet but I believe that it is coming online sometime in the next couple of months.
So, conclusions. Mini split heat pumps can work very well to single point heating in Zone 5A, two point heating works great in many cases. But the problem cases that we saw included problem geometries, that bonus room, exterior conditions on five sides. a single point in a two-story house that one air rises problem heating versus cooling, extended periods with the bedroom doors close and the setback is cycling your system on and off. And also worse energy efficiency as to boot. When we are pushing well north of 1100 square feet per mini split head, those were the cases where we did have problems for reference. If other people have data, I’d love to see it. Oversizing mini split heads is probably a reasonable strategy for heating. And use of small air handlers on the second floor, the whole door open/door close thing will no longer be a worry. So, I’d be happy to switch this over to Heather and Gail to take questions. And I’d also like to thank our builder, you know, Transformations, Inc.
Gail: Okay. Thank you to the panelists for these outstanding presentations. We have time now for a few questions. We already have some great questions from the audience and you may submit additional questions through the questions pane on your screen. The speakers will answer as many questions as time allows. We’ve got some questions here for Andrew. The first one is, under what circumstances would you recommend a production builder to explore the single point distribution strategy?
Andrew: Yeah, this is Andrew. Yes. So, I guess, what we more or less have concluded from our work is that you know, if you have a floor plan with very simplified geometry say, a single storey ranch type of house, it’s definitely worth investigating the single point distribution strategies whether it is a mini split or something else. But whenever you have these convoluted floor plans with multiple floors and bedrooms, and I think both of these presentations show that, you know, that’s still a difficult strategy or difficult instance to condition towards.
Gail: Okay. And another question for Andrew. What effect would other strategies such as thermal math or better solar shading have in a cold climate lab house, which solar heat can drive many of the comfort problems?
Andrew: Yeah, definitely. That was you know, probably the biggest problem that we had in that lab house was that it had a lot of southern glazing. And in the winter, whenever you have the lower sun angles, on sunny days, some of those bedrooms overheated and, you know, one strategy would just be to block that energy. But then, we’re, you know, we’re actually missing potential passive solar heat that we could be using. So, you know, really, what you should be doing in these cases is looking at the design of the layout of your house. And if you’re going to have a lot of southern glazing, it really needs to be in a room or in a space that is able to possibly mix with the rest of the house. And, you know, there might be other strategies such as, you know, increasing the thermal mass that could also help mitigate that effect. In this test house, it was an unfinished home. It was unoccupied, there were no objects, no beds, dressers, et cetera, in the house. And so, that might have had some impact as well on the overheating that we saw.
Gail: Okay. And then another question about the increased velocity. How do you overcome the noise?
Andrew: Yeah. You know, I guess that’s a question that people often asked. And something that we’ve found is that with the correct register, you don’t have as much of a concern with noise. You know, if you have a traditional register with a lot of fins you know, there might be potential for noise as you increase the velocity but, you know, we’ve been doing a lot of work now with high velocity, small diameter, circular diffusers. And we found that under normal operating conditions, they really don’t make the noise that people have talked about. So I think, you know, you have to have the right register, and to some extent also the duct work is going to have an impact on that, certain types of duct work also help to mute and muffle any whistling or any noise that might be generated.
Gail: Okay. And with multiple outdoor units, and even more indoor fan coils, is a distributed mini split strategy really simplified?
Andrew: Yeah. And I think that’s an excellent question. And you know, I guess what it comes down to is you know, we want to simplify the duct system as much as possible because, you know, what we’ve generally found is that the ducts are where a lot of the problems occur, you know. The air handler itself is a pretty, you know, specific unit. They work or they don’t work. Generally, there’s not issues there. An issue is with the distribution of the air. And you know, we think that actually having those individual units provides a more simple approach because you don’t have to deal with a convoluted duct work system. So, you know, certainly, it is more mechanical separate units but I think that in some regards, it can be considered a simplified system.
Gail: Okay. And one more question for you Andrew. What is the coldest temperature where the heat pumps work? Do they have backup electric strip heat or what is the backup for the mini split, if it is five degrees outside and the units can’t keep up?
Andrew: Yeah. The mini split that we had in the hot climate test house did not have a backup. And you know, temperature is never expected to get that cold in the hot climate. And I guess in the cold climate, the air handler was actually a centrally ducted air handler where we only had individual outlets. And in that case, we actually had grounds for heat pump supplying the heat. So the outdoor temperature, you know, doesn’t have that same impact on the ground source heat pump. So maybe Kohta could answer or speak more to that as they have a lot of data from you know, a cold climate with outdoor heat pumps.
Kohta: Sure. This is Kohta. I don’t remember off hand the lowest temperatures that we saw but just in general, we overview the data we had then show even in those really cold temperatures, we saw in western Mass in the winter of 2012, 2013 no problems which capacity using the mini split as the single source of heating.
Gail: Okay. And here are some more questions for Kohta. The first one is, have you done any studies with mini splits recessed in the wall, to make them more aesthetically acceptable?
Kohta: I definitely heard about that concept of trying to get the mini splits out of the way, just so that they look a little bit better, maybe they cover them up with a scrim. We have not actually done any of the type of research with Transformations or with anybody else. My understanding is that the critical thing is to avoid blocking the return and avoid creating a pocket, I believe the return is on the top for most of these units. And also, there is some risk of creating these kind of a pocket of air that gives you a false reading of what the, you know, temperature might be. I’m sorry I do not have more on that.
Gail: Okay. Here’s another question. Do required PSI exhaust fans have any influence on the effectiveness of this design?
Kohta: I’m sorry. I don’t know if I understand that question. Do required PSI exhaust fans, is that what the question is?
Gail: Yes, it is. Have any influence on the effectiveness of these designs. I’m sorry, I can’t be more clear.
Kohta: Okay. Yeah. If the questioner would like to just, uh, clarify, I’d be happy to answer it.
Gail: Okay. All right. Well, in the meantime, we’ll just go on to another question. The next one is, isn’t stratification due to colder interior surfaces more than air infiltration?
Kohta: My best understanding is that you can have a massive amount of stratification through air leakage just because the stack effect, warm air is trying to rise, it’s going to leak out of the top and then come in new replacement area is going to come in at a bottom during the very cold winter time conditions that means you are introducing a lot of outdoor temperature air at the bottom of the building. You know, walking around these houses with an infrared camera, there was no sign of uneven temperatures, surface temperatures on the inside of the house. Basically, the second floor bedroom walls and ceilings were the same temperature as the first floor for walls and floors.
Gail: Okay. And for mini split systems, is there a reason to consider HRV or ERV to keep adequate CO2 levels especially in very tight houses like in [inaudible] [01:21:54]?
Kohta: That’s a great question. You know, the focus of this presentation was space conditioning not ventilation. But that is definitely a strong point to bring up in any of these houses where we’re pushing energy efficiency and getting towards, you know, greater air tightness levels and reducing air change with outside a controlled mechanical ventilation system operating in a constant rate is definitely a key part of the whole package.
HRVs and ERVs are a fantastic approach to do this. They are the most costly system but the most energy efficient system, hands down. That being said, Transformations, they typically run in mixture of HRVs in some of their houses as well as just exhaust fans in some of their other houses. You know, people can challenge that exhaust fans do not provide very nice distributed ventilation, that is true, but it does provide some basic, the lower end of ventilation there.
Another pointed out HRVs and ERVs are, you know-- probably, we’re getting too much into the weeds, but one of the traditional ways to fully duct an HRV is to drop the outside air into the bedrooms. This makes sense? You want the fresh air in these rooms, where people are spending most of time. If you are considering a simplified distribution system, you probably want to do that with a bit of caution because, remember, we’re relying on that heat filtering from the core to the rooms and provide heating through those spaces. If we’re creating an additional challenge by dumping cool or tempered, if you will, air into the bedrooms, you’ve made the job a little harder. So I believe Morgan Holiday actually did a very nice Green Building Advisor column talking about rethinking HRV ducting, one of the simplified systems, where they’re actually exhausted, pulling from those bedrooms instead.
Gail: Okay. One final question for you Kohta. When it comes to constant setpoint versus not, do you have any impression about what installation or envelope leakage numbers would change the optimal strategy?
Kohta: Great. I’m calling it a great question because I’m kind of-- I don’t know where the tipping point is for, what could that necessarily will be. I know that the general guidance is the better your enclosure, the less worthwhile a setback is going to be. I know that the guidance that I heard from other folks is that, you know, heating the Energy Star level is probably reaching the point where setbacks become less and less worthwhile, you know, the classic place where setbacks make a lot of sense is the leaky old place in an 1800s house for sure. but I’m sorry, I can’t give better guidance than that but my general impression is we’re starting to hit the point, probably if you are an energy geek like me the stuff you building day to day might be in that neighborhood.
Gail: Okay, thank you. That’s all the time we have for questions today. Panelists, before we take our quick survey, do you have any additional or closing remarks you’d like to make before we close the webinar?
Andrew: This is Andrew. Yeah. I guess, just thank you for your time. I hope that you know, the data we presented and the things we discussed have gotten you thinking about some alternative strategies and aware of the challenges and in some instances, now that we’re learning the advantages with these alternative strategies.
Kohta: Yeah, this is Kohta. Thank you very much for your participation. We appreciate it.
Gail: Okay. Thank you again to our speakers. Now we’d like to ask our audience to answer three short questions about today’s webinar. Your feedback will help us to know what we are doing well and where we can improve. The first question asked, whether webinar content was useful and informative. To answer, click on the radio button right in the GoToWebinar panel.
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Thank you for taking our survey. Stay tuned for the next building America Webinar on November 19th at 3pm Eastern time. This webinar will review Building America research results. Registration will be available soon on the Building America website. On behalf of the Building America Program, I’d like to thank our expert panelists for their time today and to our attendees for participating in today’s webinar. We’ve had a terrific audience and we appreciate your time.
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