High Performance HVAC Systems, Part II: Low-Load HVAC Systems for Single and Multifamily Applications
November 16, 2015
- Andrew Poerschke, Building Performance Specialist at IBACOS
- Anthony Grisolia, Director of Product Information with IBACOS
Nicole: Hello everyone! I am Nicole Harrison 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 Anthony Grisolia here to discuss low-load HVAC systems for single and multifamily applications.
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We have an exciting program prepared for you today that will discuss the current research on comfort in residential buildings. Results will be presented from 37 new homes that were monitored in the Southeast United States. The presenters will also discuss results from a modeling exercise that identified the impact house design, system design, and control strategies have on comfort and energy consumption. IBACOS has begun investigating a plug and play duct system that is intended to significantly simplify the design and installation process of ductwork, as well as reduce the risk that poorly installed ductwork will hamper performance. Finally, IBACOS will discuss the differences in performance of a standard system, a small diameter system, and a ductless mini-split system in a set of new construction town homes.
Before our speaker begins, 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.
The U.S. Department of Energy’s Building America program has been a source of innovations in residential building energy performance, durability, quality, affordability, and comfort for 20 years. This world-class research program partners with industry to bring cutting-edge innovations and resources to market. Visit our website at buildingamerica.gov to find more information about the program and the Building America Solution Center, which provides expert information on hundreds of high-performance construction topics, including air sealing and insulation, HVAC components, windows, indoor air quality, and much more.
Building America is supported by 10 industry research teams and four national labs. Each of these teams and labs partner with dozens of industry professionals, including builders, remodelers, manufacturers, and utilities. The best and the brightest in the residential buildings industry can be found here.
And now, on to today’s presentation!
Our webinar today is High Performance HVAC Systems, Part II: Low-Load HVAC Systems for Single and Multifamily Applications
If you would like more detailed information about this effort, please feel free to contact our speakers.
Our first speaker today is Andrew Poerschke, a building performance specialist at IBACOS. He conducts research in building performance for IBACOS. He uses his expertise in sensors and monitoring hardware to design and implement remote data acquisition systems to monitor test buildings, and analyzes the performance of HVAC systems using test house measurements to calibrate transient thermal models. He is proficient in advanced computational analysis using the latest statistical software packages, which he uses to analyze and visualize large data sets in new and insightful ways. Andrew is also involved with product innovation for major manufacturers at IBACOS, testing new systems and evaluating their performance against established metrics. Andrew previously assisted in the commissioning of the EcoCommerical Conference located on Bayer’s Pittsburgh campus. He is a graduate of The Pennsylvania State University where he studied Energy Engineering, and participated in 2009 Solar Decathlon.
Our next speaker is Anthony Grisolia, who is Director of Product Information with IBACOS. He oversees IBACOS consulting activities and services for product and material manufacturers, including technical services and testing for existing products, development of new products and markets, and evaluation of product opportunities. Anthony also helps support production homebuilders, having evaluated hundreds of residential construction issues and performed construction quality assessments with builders in 40 different markets. He acted as principal Building Scientist for the construction of DIY Network's Best Built Home and regularly develops specifications and conducts quality assurance for green communities. In 1999, he was honored with Canada's Energy Efficiency award for an energy efficient housing design. Anthony has a Master of Architecture degree with an emphasis on Sustainable Design from State University of New York at Buffalo and a Bachelor of Building Science degree from Canada's Ryerson University.
With that, I’d like to welcome Andrew to start the presentation.
Andrew: Alright, hello there. This is Andrew Poerschke and Anthony Grisolia. Thanks for joining us today. Today we will be discussing low load HVAC systems for single and multi-family applications. We have our agenda here, today we will be going over some of the research IBACOS has done in the last year investigating the performance of HVAC systems specific to low load homes. We will talk about a large scale study where we monitored 36 homes in the Southeast. We will talk about a modeling study where we did a large number of energy models to look at the comfort of some different systems. We will be reviewing a key study where we compared the performance of a small diameter system to a traditional duct system in a multi-family town home, and finally we will review some of the results of an effort we are conducting to develop a plug and play duct system. Then we will discuss where we are going with some of this.
So first we are going to jump right into the data from this study of 36 homes. We monitored the temperature in humidity in all of these homes in the significant rooms in the house. So we put about 5 sensors in each home and collected data over about a 2 month period. All of these homes are located in the US Southeast, in Tampa, in Orlando as well as San Antonio and Houston. We monitored all of this data to get an understanding of the current state of the performance of the state of new homes. All of these homes were built in the last few years and they were built by homebuilders promising high performance and also offering a comfort guarantee on their homes. So because these houses had a comfort guarantee, we were working under the assumption that the occupants would in fact be comfortable. So we could go in, take these measurements, review the data, and start to get an idea of different circumstances in which people were comfortable that might not necessarily align with industry expectations of comfort. Just to give you a quick overview of what you are seeing here, again this is all the data from all 36 homes. We are plotting the actual temperature measurement and you will see that time is on the horizontal axis, and we are actually plotting each temperature measurement on the vertical axis grouped by the home. I’d like to just point out a few homes here – homes 24, 25 and 26 these homes are all located in the same neighborhood and on the same street. You actually see pretty different temperature patterns in those homes.
Anthony: And they were all built to the same energy efficiency code, 2012.
Andrew: Yes. They were all built to the same efficiency code. The only difference in these homes are the occupants and their behavior. In home 25 you can see that the temperature is relatively consistent over time. However home 24 and home 26 you can see some different behavior, perhaps an automated thermostat setback.
So we are starting to understand a little bit more about what occupants are actually doing in their homes. So to step back for a minute, I just want to talk a little bit about how IBACOS thinks about comfort. Comfort in general is a subjective feeling of satisfaction with the thermal environment. Everybody has a slightly different idea of what that satisfaction might be. So we’ve found that looking at not as much specific temperatures but to look more at temperature uniformity across the home gives us a better understanding of comfort and a more quantitative way to diagnose potential comfort problems between homes. So some of the specific numbers we will be talking about today are drawn from ASHRAE manual RS which discusses comfort in homes, and that manual says that each room in a home should be within 3 degrees Fahrenheit of the thermostat during the cooling season, and 2 degrees within the thermostat during the heating season. And along with that then, every room in the home should be within 6 degrees of the other rooms during the cooling season, and 4 degrees during the heating season. So we will keep coming back to this room to room metric, where perhaps the top floor is at a warmer temperature, and the bottom floor is at a cooler temperature. According the ASHRAE manual RS they should be within 6 degrees of each other. And one other metric that we will discuss related to ASHRAE standard 55 and that is temperature uniformity over time. According to that metric, the temperature of a room should not change drastically in a short period of time. For example, it states that in a 15 minute period of time, the temperature should not change by more than 2 degrees Fahrenheit. So we will keep coming back to these numbers but I just wanted to give a quick intro so that you are familiar with them.
So we are going to start with looking at ASHRAE standard 55. These are the same three homes that I highlighted before. These homes again are on the same floor plan, same street, same orientation, the only difference is the occupants. What we did was select data from three days in September and plotted it on a Psychometric Chart. As well as doing that, we drew the ASHRAE standard 55 comfort box onto that plot. That box is representative of an occupant wearing typical clothes. It is a 0.5 clothing value, and that assumes pants and a long sleeve shirt and a 1.0 MET rate, which is a metabolic rate and that’s pretty standard for someone who may be sitting in their home and not doing any active physical activities. What we found when we started plotting data on one of these charts was that there is a wide variety of preferences within a home. So again, all of these occupants were working under the assumption that they are comfortable. They have the ability to set their own set points and if they decide that their home isn’t comfortable, they have had opportunities to get that fixed. So what we found was that for example in one home, the rooms are within that box 7% of the time and another home the rooms are within that box 0% of the time. There is this wide variety of temperatures that people think are comfortable. In one case, the average temperature is around maybe 77, and in another case the average temperature is around 72. And these people are neighbors, so there is a wide variety of expectations for comfort.
So let’s look at all 36 homes at once. What we have done here is selected the data for the entire month of September for all of these homes, again they are all in hot or humid climates in the Southeast, and they are all relatively new homes. What we found is that according to the ASHRAE comfort box, that the rooms in that home were only in the comfort box 47% of the time. From that actually the median set point, if we just look at the thermostat temperature, the median set point was 75 degrees. So people at least in this climate at least in these homes, seem to have an expectation of comfort that is somewhat different perhaps than the assumption.
Now to change gears a little bit, we are going to discuss comfort according to ACCA manual RS. Again, in this plot, we are looking at all 36 homes for the entire month of September. What we’ve done is calculated the room to room temperature difference at each time step and then done a cumulative summation of that over time to understand the total percentage of data that lies within a certain temperature band. So for example what we see here is that 95% of the time – so this green vertical dashed line – the maximum room to room temperature is 6 degrees Fahrenheit or less. The closer this blue curve is to 100% represents the majority of the data being under that curve. So the ACCA threshold is 6% and again, what we have found is that these homes according to the ACCA threshold were comfortable 95% of the time.
The next question then is how does that relate to a home builder? The home builder is interested in understanding their potential risk of comfort callback. When a consumer is uncomfortable in their home they either call the builder or the HVAC contractor and somebody has to go back to the home and fix things, and that ultimately costs them money.
Anthony: Yeah, so from a builder’s perspective we get these questions a lot, where we get comfort questions on a specific building and we are trying to understand – is the ACCA standard actually valid enough? We hear builders complaining about homeowners being uncomfortable when there is a 3 degree difference instead of a 6. So we are trying to understand, where is that point in time where there is a lot more risk for a builder. Is it 3 degrees is it 6 or is it 10? So we are trying to understand that from a lot of this data that Andrew has been presenting so far.
Andrew: So we don’t necessarily have the answer to that yet, and from a builder’s perspective it would be great if they could understand that, yeah, this home the way it is designed has maybe a 5% risk of getting a comfort complaint. Whereas a different design that is maybe not quite as well preforming may have a 10% risk, and we don’t have the data yet to fully fill in this picture but it’s something that we are interested in and somewhere we think we are going to understand comfort in homes.
Continuing with this same data set, and I just want to show a couple more interesting things we discovered. We really wanted to dig into some of the potential factors influencing comfort in these homes. Whenever we installed the sensors in the home, we also did a brief survey of the occupants, to understand things like: are they full time employed, or are they part time, to understand whether or not they use a programmable thermostat, and whether these factors might influence comfort in their home. What we found at least with these two factors was that there wasn’t a significant trend that perhaps depending on their own lifestyle, even if they were full time, or part time or retired even that the room to room temperature in that home depended on many other factors.
One of the factors that had one of the most significant impact was the number of stories. This is to be expected. You have a two story home, you are going to get more temperature stratification. We found that the room to room temperature on average was 3 degrees Fahrenheit for the two story homes, whereas it was only 2 degrees Fahrenheit for the 2 story homes. Little bit more evidence showing that the more complex in your building design, there is a little more risk for comfort issues.
One other thing that we monitored in this study was the humidity in the homes. Now these homes again were in a humid climate. However, they did not have any active de-humidification. There were no dehumidifiers or other supplemental equipment. It was relying purely on the installed centrally ducted HVAC system to provide de-humidification. Looking at this plot, any of the areas that are shaded magenta, represent periods of time when the humidity was above 60%. What we found was that there were really only a few outlying pieces when humidity was to that level. Just speculating about some things for example, in one of the cases, this home 2 that we’ve highlighted, that home was very similar to homes 1 and 3. They were in the same neighborhood, same builder, however home 2 had a gas stove whereas the other homes had electric stoves. One possible source of humidity in that home, and it might have made all the difference. However, in general, what we found was that humidity levels were able to be maintained at an acceptable level which is something we found to be a little interesting and perhaps a little bit unexpected in this very humid climate especially considering the data that we are looking at is also at the beginning of the shorter season. In October, the system isn’t running as much, but there wasn’t a major humidity problem.
To recap some of the key lessons learned. Comfortable occupants aren’t necessarily the same. People have different expectations, different preferred temperature profiles and you really have to look at a variety of different preferences when designing your home to provide the best comfort to everybody. Room to room temperature uniformity is a better metric perhaps than looking at a single temperature band, that way an occupant can set their thermostat to whatever they want, and we can still understand how the home is preforming. As we said, finally humidity was maintained below 60%, the majority of the time, even without any supplemental de-humidification.
So now we are going to change gears to the next project that we are going to discuss. That first project was really to understand, in the field, in the real world, in homes that are being built today, what kind of conditions are people experiencing. Then to kind of extrapolate some of that knowledge, to different climate zones, to different house types, to different HVAC system types, we can understand the impact of different control strategies. We conducted a modeling exercise using a total of 99 models. These were TRNSYS models: Multizone thermal simulations so that we can understand what the temperature in each room and the impact that these different factors would have on the temperature in each room. We also used a compound model to help us understand the impact of airflow between the rooms.
Because we are really looking at systems, we have to be very accurate with airflow. So we chose to use a compound model as well. A little more details about these 99 models. Each of the homes was built to the appropriate zero energy ready home standard for that climate region, which is very similar to IECC 2012. The three different systems that we studied were basement, ductless heat pumps. We studied traditionally ducted central system, then finally a small diameter system. We also looked at 5 different control strategies. We looked at the standard single zone, single thermostat, we looked at – well what if you put an additional thermostat into that home in perhaps the second floor? What kind of impact do you have there? So we have a single zone, but two thermostats that can turn on that virtual air handler. And then next we looked at a zoned system, where perhaps you had two zones and two thermostats to give a little bit deeper level of control. The last two control scenarios involved running the fan in periods when the system wasn’t calling for heating or cooling to understand the impact of perhaps continuously running your fan on comfort. The final case, the model actually made some decision on whether or not it thought that there was a potential for a comfort problem. Say, during a very sunny day during the shorter season and it kicked on the fan during that period, to see if it had much impact. Then finally you see the pictures of houses that we actually based these models off of. So we based each of these houses’ geometries off of real world homes that we’ve studied. We picked three different house types. One of those was a single story home built on a slab. One of those homes was a two story home, again, built on a slab, and the third case was two story home built over a basement. So this way we would have a variety of geometries and also a variety of window orientations and window area to better understand the impact on comfort, from these various design decisions.
On this slide, we are showing the results from all 99 simulations. What we did was calculate the room to thermostat temperature difference. So if you remember that should have been within 3 degrees during the cooling season and 2 degrees during the heating season. We have calculated that difference for the entire year long simulation, then we tabulated those numbers as a histogram to understand how tight are those rooms. In an ideal scenario, all of the temperature scenarios should be closely aligned with the thermostat. In this first case of the single story ranch style house, in the Orlando climate zone, we see that there is a relatively tight clumping around the center. Something else that we have done, is then counted the percentage of time that all the rooms are within the plus or minus 3 degree or 2 degree band, and we are looking at those numbers. What we did was highlight in green all of the cases in which the home was comfortable by that standard at least 95% of the time. In some instances, across this vertical column, the vertical column represents one home in one climate zone, and we see then the impact of different HVAC systems and the impact of different HVAC systems and the impact of different control strategies. What we see from this graphic here is in general, the simple floor plan was the easiest to condition. That is what seems to be expected. If you have a simple floorplan, you don’t really need that two zone system. And there is really not a significant performance difference between mini splits and a centrally ducted system. Across the board then we find that in other cases the mini splits do perform better when you have multi stories in which you may have temperature stratification or if you have a different zones that have perhaps more glazing or less glazing it’s very important to have that zoned approach in which the HVAC system can respond to the unique load profile of the room. One of the things that we thought was interesting was that the continuous fan mode we thought that across the board it would significantly improve comfort. We are mixing all the air within the house it should provide a much more uniform temperature and in some instances it did. That two story home over a slab, it actually did improve the comfort. In another case, that two story home built over a basement, it actually reduced the comfort in the home by a few percentages. It reduced the amount of time that the homes were within the comfort bend which is something unexpected. The big takeaway from this study was that there really is a strong relationship between your architecture or your home, the geometry, the way that the rooms are laid out, the way that the windows are laid out, and the system ultimately decides to put into that home. And with the low load home, you have to be very careful in designing your system such that you don’t encounter these types of comfort problems.
Just to zoom in a little more on that data, we’ve excluded the small diameter system from this particular data set. We found that the model didn’t significantly capture differences between a traditional system and a small system. So we are just going to zoom in to really look at the impact of the different control strategies. We found that in some cases for example in Orlando, the model showed overheating because the climate there isn’t nearly as cold as the other climate zones – the home actually warmed up because of solar heat gain in the winter up to a temperature beyond the thermostat dead bend, but it was still below the cooling bend so it looks like it’s an uncomfortable period, but it’s likely that an occupant in there wouldn’t be uncomfortable. But what we were able to find by looking at the data separated out according to time of the year was that in some instances, you really needed to perhaps rebalance the system to provide optimal comfort during different times of the year. Now that’s a challenge with a lot of currently installed systems. There might not be access to balancing dampers if there are balancing dampers maybe they are set once and sealed off in a cavity and with these low load homes we just have different profiles at different times of the year. It’s really really highlighting need to be able to change the airflow to different rooms at different times of the year.
So one of the things we did here was actually plot the temperature data on a floorplan for one of the homes. So this home is the two story home built over the basement. We see on the bottom in each of these cases we see the second floor on the top of the first floor, the white box represents the garage. This is an unconditioned garage and we chose not to include the basement on this particular plot, just to focus on the occupied spaces. What I’ve done then is pulled out four specific cases to really look at the impact of these different control strategies. Again this was the two story house built over a basement and this data is from the Denver climate zone. If you look at our timer, we are starting to look at data, starting in July. This is the summer. And we will see as the day begins, the system starts to cycle and you have all these various cycles and you start to see that some systems are preforming better than others. So when the sun comes out we see that the southern bedrooms in some cases are starting to heat up significantly. In the case of one zone one thermostat, the top floor is actually significantly overheated, whereas the bottom floor – the thermostat is only sensing the temperature on that bottom floor and it is still quite comfortable. So if we then consider the case where we then decided to put two thermostats connected to that one central system so the box from the bottom left, we see that the southern bedroom and the second story in general is at a more comfortable temperature, but what happened was we overcooled the bottom floor. That bottom floor didn’t need any cooling energy, but it was still supplied. So in this case what worked the best is actually a scenario with two zones and two thermostats to provide optimal comfort. You see the continuous fan scenario didn’t significantly improve the comfort in this particular case. In a different case it did however.
Briefly again, we will look at this similar animation in the winter. We see again the southern bedroom tends to overheat during the middle of the day when we have the strong solar radiation. In this case there is really not a significant difference between the different control strategies. Again, the continuous fan, yeah about one room is starting to overheat, but the continuous fan didn’t make a significant impact in mixing that home.
So some of the lessons learned from this modeling exercise is that considering the architectural design and mapping of the home is crucial whenever you are conducting the HVAC design. Especially in a low load home. Something that works in one home might not work well at all in another home. At the same time with simple homes you don’t need a super complex control strategy perhaps. If the design with overhangs and good shading you can actually provide great comfort providing the single zone single thermostat system. You really have to consider all of these elements simultaneously to maximize comfort. Window orientation and the percentage of the window relative to the wall area is a significant factor. In some of these cases two thermostats were necessary. And actually what we found was that in some cases it makes more sense to put one thermal zone on the southern side of the house and one thermal zone on the northern side of the house. Typically a two zone system might be a top floor and a bottom floor, but that might not always be the best case to maximize comfort. Something else that we noticed was that in climate zones with large temperature swings between day and night like Denver or Fresno, there is actually an opportunity here by increasing thermal mass perhaps to improve comfort.
To bring this back again to the real world we wanted to talk about the shrinking thermal load in homes relative to the amount of air that’s being applied in homes. So in the past, looking at this top case you might have installed a 5 ton air conditioner in a typical 2000 sq ft home that was blowing 2000 CFM. Now as we continue to improve the thermal envelope the size of the air conditioner is getting less, the amount of air flow being supplied to these rooms is less. We are stepping down to say a 3 ton system or even a 1 and a half ton system, but the floor area is the same. We are still dealing with the same 2000 sq ft home. This is one of the significant challenges that is causing comfort problems. We are dealing with less air, the same floor area, we have to be more smart about how we are using that air to provide comfort in the home.
Here is some data that we have plotted from a recent study. Both of these homes are high performance homes, one of them is in fact a passive house, which is a super inflated home, and should prove to be very very comfortable. But what we found was that even in a passive house you can have temperatures well beyond that specified plus or minus 3 degrees temperature range because the HVAC system isn’t responding to the unique thermal loads of individual rooms. There is an opportunity here really to improve the way systems are designed, installed, and as we mentioned before there is a need really for adjusting the air flow based on the season. In a passive house, especially you can end up with significant solar heat gain, and that is one of the design elements. You are trying to maximize your solar heat gain in the winter. What can happen is, if the heating system is still supplying the same amount of air in that room, you can end up with significantly overheated rooms.
Anthony: And this is – these two homes are both in the same community and this is the perfect example why IBACOS believes that energy efficiency does not equal comfort. These two homes are pretty high levels of insulation and air tightness, so this is one area that we’re trying to dig in to further understand comfort conditions in low load homes.
Andrew: Yup. So as we said before air delivery is key. We have gone from these big ducts, lots of CFM and we are just naturally as loads are going down reducing the amount of air flow. As a result, these duct systems, these air delivery systems need to change to continue to provide maximum comfort.
Next we’re gonna look at the key study of the townhomes this project was conducted in Denver, CO. It was in the Stapleton community and these townhomes were built by New Town Builders. What we wanted to do in this study was compare the performance, again, eliminating small diameter systems to a traditionally designed and installed system. So we looked at a case where we had 3 unit townhomes, so there were a total of 6 homes that we studied in 2 separate units. The data that we analyzed was from the cooling season. To go a little bit more into the detail of these homes, you see that there were a total of 6 units, 6 homes studied. They were on the same street, the two buildings were side by side and in the same solar orientation. So this is really a great case where we have minimized the number of possible differences between the homes and we can really start to understand the relative performance of say a small diameter system to a traditional centrally ducted system. In this project we also looked at installing mini split heat pumps. I’ll get into perhaps some reasons, but we weren’t able to analyze the data from that house, because it was unoccupied for the entire study period. Each of these homes as you can see in the picture, were three stories tall. One of the issues that the builder was encountering was with this three story town home there was a significant amount of temperature stratification between floors. They wanted to find an efficient system which could provide better comfort and also allow them to bring duct work in the conditioned space and also maintain the efficiency level that they are expecting.
Going into some of the home specifications, each of these homes the installed system was between 1 and a half and 3 tons. The design loads were between about 1 ton to 1 and a half tons, and then that equates to a sq ft per ton inch of around a 1000. Older homes you might have had a sq ft per ton of around 400. What we are talking about here with these high performance homes is closer to 1000. It is a pretty significant change with these high performance homes. Just to reiterate, we had the three cases B1 B2 B3 where this is the builders standard home. Putting in their standard heating and cooling equipment, and in case A1 and A2 and A3, we looked at small diameter system and also mini split heat pump.
Each of these homes was built with the same level of insulation right around IECC 2012. There is not differences in that regard.
Anthony: I want to just talk about the differences between the air distribution systems between the traditional home that had traditional ductwork vs. the small diameter home. So, the traditional home which were the B models that Andrew went over and based in traditional ductwork sheet metal. The equipment is located on the main level of the home, then basically trumps the distribution through the main floor then larger distribution branches then ducts that actually branch to the exterior wall. Conventional thinking of trying to wash the exterior walls with conditioned air, so very traditional a lot of chases that occupy architectural living space. This was the standard that they want to understand what is the better scenario to improve comfort.
So the small diameter high velocity system that the other several homes used was very small diameter trunk, we located the air handling closet on the second floor and we basically distributed up and down from there, so very small compact duct systems, so very short supply and return trunks and really short branch ducts. The strategy here is how much less duct work can we use and how far can we throw this air to the exterior wall to continue the throw of air.
This is a picture of what we did to keep ducts in conditioned space, so you will see the round larger duct is really the supply coming up to the third floor, and you will see we basically did a drop ceiling in a closet about 10 inches to fit in above this trunk, then really short branch ducts to throw air to the exterior walls of the room. The ducts branch sizes were 2.5 inches, so we are going to 8 to 6 inches down to 2.5. Significantly reducing the size of the air distribution system.
Andrew: Next we will dig into some of the performance differences between these systems. So to begin, the builder was concerned about stratification between floors in these three story homes. We wanted to see if the small diameter system can perhaps improve upon that performance. What we’ve done here is plot the room to room temperature difference again of each of these homes over time. The higher the room to room temperature difference the worse the performance is. That magic number that we are targeting in the cooling season is 6 degrees Fahrenheit. The only period in which these lines are beyond 6 degrees represents a failure of one particular metric. What we see here is that one of the worst preforming homes is B3, and there is times – that’s one of the end units – there’s times whenever that home is actually the top floor is 10 degrees or more warmer than that entry level. And that is what the builder is trying to avoid. So we kind of verified that yes, there is perhaps a problem with some of their central systems. Now if we also look at that middle unit, B2, and B3 we see that B2 for example preforms a little bit better and B3 is preforming perhaps not quite as well, but B1 actually does preform similarly to the small diameter systems. The two cases of the small diameter system are the solid blue line and the solid green line A1 and A2, and most of the time those homes actually have the best uniformity. There’s a few spikes in there and it might have various reasons. Perhaps they opened the door, we don’t know exactly but on average those homes did perform better. Let’s talk a little bit about home E3. That was the mini split heat pump case. That is the red line. We see that it also appears to have pretty bad temperature uniformity when in reality when you think about it what we did was have a total of 4 head units in this home. One on each floor and actually 2 on the top floor. So in theory, that top floor could be very very close within one degree, say of the bottom degree of the bottom floor. What happened was the home wasn’t occupied and the thermostats were set to very different temperatures and one of the thermostats was actually set to 80 degrees. So that is why you see this pretty significant temperature difference in that case. Again I wanted to show the data on this psychometric chart, not going to get into too much details, but what we are seeing is some pretty significant differences from the measured data to perhaps what you might expect just based on that comfort box.
Then I want to dig in a little bit to the room to thermostat temperature difference. What we’ve done here is to actually plot in each of these cells the thermostat temperature for that home against the room temperature in one of several rooms. We are looking at the entry level, we are looking at the foyer. Then we’re looking at the master bedroom and one of the other bedrooms. And we are looking at how the temperature in those rooms compares to the thermostat. Now according to the ACCA standard, there should be a 3 degrees of the thermostat. SO that room is too warm or too cool, we will see it on this graphic. The top two cases, A1 and A2 with the small diameter systems. Then we see that there is some occurrences beyond that plus or minus 3 degrees temperature bend but in general those rooms are more comfortable. For example, this bedroom 3 that room did face – or bedroom 2 – did face south, so it’s likely that’s why this room showed more failures than the other rooms. Then look down at the builders standard system, there was one case in which that system preformed pretty well. It’s possible that maybe this system just had the right installer on the right day and the stars aligned and it worked the best. Then there are two cases in which that home didn’t have quite as uniform of a temperature and that’s when we saw that 10 degree temperature delta between the top and bottom floors. Something interesting to compare however is that in the case of E2 in the entry level here, the foyer on average the temperature of that foyer was actually warmer than the thermostat, even in the summer. Now this is a room that faces north, so perhaps the reason for that is that it was getting more airflow in the summer than in perhaps heated. Now in the case of B3 we see that that entry level was 4 degrees cooler in the summer. That’s a little bit counter intuitive, and again it is possible that there might have been more air flow going to that room than it needed. In the winter, we might actually see better performance in that case. If you think about it, we are supplying in the winter warm air to that bottom floor, so it’s going to tend to want to rise and mix better with the rest of the house.
Next we’re gonna talk a little bit about the energy use and how it compares between these different systems. We want to provide comfort, but ultimately we also want an efficient system. What we’ve done here is calculated the total energy consumed by the cooling system of each house across this 9 day period. That’s the air handler plus the heat pump. Just to point out a couple of little anomalies, in case of home A1, so the solid blue line, and that home was not occupied for the first few days and as a result, that system was turned off and it looks like the end of the day, the energy use was a little bit lower than it should have been for that home. If we normalized it, you’d see that it used a little bit more energy than we are seeing here.
Anthony: Yeah. And a couple other items that would affect the energy use of these homes would be the small diameter high velocity system, it uses a little bit more fan energy because of the increased pressure and the velocity of the air moving through the duct system. And also the massing of all these homes and the volume of all these homes are different. So the volume will create a little more of an energy load, so those are some other impacts that will affect these 6 scenarios.
Andrew: One other thing I’d like to point out on this graphic is that home E3, so the unoccupied home, it actually had the most energy consumption, and that’s also despite the fact that during the summer, some of the set points were 80 degrees for those indoor units. So why was it using so much more energy? We can make a couple guesses. That home had no window shades installed, and there was a decent amount of southern exposure for these homes. All of the other buildings that were occupied and they had blinds or other shades installed on the interior of the home, so that might have made some impact. Also, in the climate like Denver, you do have some cool evenings, and it’s possible that the occupied homes were able to take advantage of natural ventilation that they could open the windows at night and get some free cooling and turn off their systems. Of course that wasn’t the case for the unoccupied home. I think it does highlight an interesting need for shading, and the impact that that can have. Which might be pretty significant on energy consumption in a home.
To look at the summary of these, we can look at the room to room temperature difference, so the bottom line on this table, if we compare home A1 to home B1, we see there is a slight performance improvement on A1. It was 2.4 degrees different on average relative to 2.6 degrees. Home A2 vs. B2, it’s a little bit more stark. Home A2 only had a 2.1 degree temperature difference vs. 4.8 form home B2. Energy consumption like we are seeing with similar of course with the small diameter system, you are going to use a little bit more fan energy. What we found was that it wasn’t that much different.
Next we are going to talk about our home run manifold system.
Anthony: Yeah, so Andrew’s going to talk about some of the work we are doing investigating air delivery strategies, where utilizing smaller diameter ducts, so like Andrew said over the last half hour, low load homes is the trend, that means we are using a lot less energy in the home which means there’s a lot less air flow in these homes. But we still have the same volume of space in these home that we have to condition, so we are focusing on how to bring air delivery to each of these rooms effectively and also how do we maintain comfort in each of these rooms with a smaller volume of air distributed. So one of the things we are looking at is sort of potentially similar strategies as to what the PEX water industry has looked at over the last 15 years, where they looked at remote manifolds of distributing water. Well thinking of water as air, could we use the same sort of methodology to bring air to these homes with smaller pipes. The other thing we are looking at is what are the challenges with different duct materials? We know there are challenges with the codes today, with thinking of duct material that are beyond fiberglass, or beyond sheet metal. Those duct materials today like flex duct, like sheet metal and duct board, meet the code standards the UL181 and ASTM 884, so we are looking at potential other materials that could fit in this space of small diameter ducts. There is a lot of value to this. Our builder partners, they see the value in smaller diameter ducts, because it helps them potentially standardize duct layouts, and also helps the trades effectively install duct systems in homes. Typically today we see a lot of duct work in homes very sporadically laid out, very ineffective and which could potentially cause comfort issues. So, we are trying to crack this nut. If you think of duct work in homes, it is the bastard stepchild in homebuilding. No one really thinks about it. So we’re trying to attack it to try to make it better. So that’s what we’re really focused on at IBACOS. So Andrew’s gonna talk a little about what we’ve done over the last year and what we continue to do in the next year or so.
Andrew: Yeah, so if you think about this traditional duct system that nobody really wants to think about, historically, the way these are designed is to go through a series of design manuals and calculate the load on the home, you size your system, and then hopefully you start to think about the duct design. The way that that is designed is you have many many different sizes, diameters of ducts, run outs, different sizes of branches, and ultimately the idea is that by reducing the size of your trunk, and as you take more and more take offs, you are able to hopefully maintain the air flow you want to the longest trunk. Now the chances of one of these systems getting designed correctly poses some risks. The chances of one of these systems actually getting installed correctly is even more of a risk. And so we are trying to look at a different methodology which perhaps would eliminate many of these risks. Like Anthony said, we are considering this home run manifold system. Instead of sending one duct to a room, and specifying that that’s a 4 inch by 8 inch register and everything. Instead, what if you designed it such that you had 2 or three ducts of the same size so you are always using a 2 and a half inch duct. And you know that that duct gives about 20 CFM then you can significantly decrease the amount of effort required to correctly design that system. So that’s what we are trying to understand here, with this Home Run scenario, can you get that predictable air flow out of that duct and under what sets of range can that be the case?
So, we are going to look at a little bit of data here and discuss the impact of that. Again, just to be a little bit clearer, we have this little cartoon comparing the traditional duct layout, where you often have your duct work outside your conditioned space, you have a big air handler, and it’s very challenging to actually get the air flow that you need to the specific registers. Once the air flow gets there it’s gone through so much duct work that it might not even be the temperature you want. If you compare that then to the home run manifold system, which can be located much more centrally in a home, your duct runs are ultimately shorter and if they have the smoother duct material, you actually eliminate a lot of the static pressure, just by shortening those runs and having the smooth material.
One of the things we did in this study, actually what we did was we started by looking at different manifold designs. We are not going to get into the details and results of that, but I wanted to discuss a little bit of this mock up case, where we take the best manifold design in which we had this nice even row of outlets coming out of that manifold, and connected to the ductwork. So the ductwork layout that you see here was designed for the second story of a large home. This was about a 2500 square foot, maybe a 3000 ft. home, and we decided that a home that big we really needed two of these systems. So we wanted to see how it would perform if we considered one system on that top floor. So you can imagine this duct system its laid flat right now, but if it was unfolded the right way, it would actually fit into about 4 rooms in the top floor of that house.
So what we wanted to look at was the relative air flow coming out of this different duct runs. We understood that this was gonna kind of be an extreme case. One of the duct runs was only 5 feet. One of the duct runs was 36 feet with a number of elbows. That’s a total of about 8 times longer than a duct run, but what we found was the air flow was 24 CFM in the 5 foot case, and 14 CFM in the 36 foot duct case. Not quite half the air flow for very significant change in duct work. If we eliminate some of those extreme conditions, what we found was that the air flow coming out of the duct run, was within about 20% of each other. So if we said perhaps the minimum range is 10 feet and the maximum length is 25 feet there is about a 20% spread in total air flow coming out of these ducts. We think there’s a lot of potential to this system. Some of the other important factors that we are considering is the total static pressure of that system. At 51 Pascal’s, it’s not that significant. One of the other metrics that we looked at was the total CFM that we could supply with this system. We took an off the shelf, ducted mini split, connected it to this system, and we were able to get 176 CFM through that duct work. Now that system was designed to supply 250 CFM so the one time ducted mini split. So it definitely reduced the CFM, but we think there is some potential here by putting in a slightly more powerful motor, you could get that airflow that you need.
One of the things we did to understand the potential there was to actually connect a booster fan which in this case was a duct blaster. We connected this to the return (inaudible 1:04:43) of that system and continued to ramp up the airflow to higher and higher CFM, then we measured the static pressure in that (inaudible 1:04:53) to see how it would compare. SO what we are looking at here in this chart are two different types of curves. The black curve all represent fan curves. If you just had an air handler, sitting out in the open, and connected different duct systems to it that had progressively more and more restriction, you are going to naturally get less and less airflow. So that’s why on the black curve the CFM is reduced, the static pressure increases. And then the red curve represents the other half of the story, the duct system. The red curve represents, if you have different fans connected to this same duct system, what kind of air flow are you going to get? In the intersection of those two curves is how any particular combination of systems will perform together. What we found was, down there at the bottom range of that system, we just connected it to an off the shelf ducted mini split, the static pressure was around .2 inches of water column, and we are getting that 176 CFM of air flow. But if we continue to ramp up that air flow, we are going to need a little more static pressure. But at around 250 CFM we are still below .4 inches of water column, which for many air handlers is a reasonable number. We think that there’s a lot of potential to this system. So looking at the static pressure which is really, perhaps one of the significant challenges to this system, or we thought it would be a potential problem going into this project. We have actually found that that static pressure isn’t as high as we thought it would be. And we were able to get the air flow we need without really cranking up that motor and burning a lot of extra energy.
Anthony: Yeah, and I guess the other things to note on this graph is, you saw the picture of our mocked up duct system. We used PVC pipe. Not a duct pipe. But it has a very smooth inside wall. We believe that has an impact. And the duct system was really airtight. These are some little things that may tell us why we are getting some of these results.
Andrew: Yup, yup. So the summary of findings for this particular project was, yeah, we found the manifold system for this project did actually show predictable airflow out of those outlets. Was it always the same? Were we always getting 20 CFM regardless of the length? Well, no. That is to be expected. However we did find that the airflow wasn’t that far off, if you establish a reasonable set of design requirements. Again, the static pressure was minimized using that smooth duct work. Also what’s important was the compact duct layout. By routing duct work through floor cavities, even though interior partition walls, you are able to get the duct work right where it needs to go at the minimum length. So that’s one of the really big advantages of this system, is to be able to bring the system into a very compact area, and you are also minimizing the impact on perhaps other livable areas by using some of the existing cavities in the home. We did find that the system can supply enough air flow to meet the demand for a low load home. Larger homes you may want to start thinking about 2 of these systems. But if you are thinking about it as a mini split, it’s not inconceivable to have 2 or multiple indoor units and a single outdoor unit. And then something else that we’ve thought about with this system, because you are running all the duct work back to that central location, you actually have a lot of potential for seasonal balancing to get the exact air flow you need into a particular room, and this is something that the existing method is to install balancing dampers. Typically they should be installed right after a branch comes after a trunk, the main trunk of your duct. Well where are those branches typically installed? Maybe within the attic? Maybe within a wall cavity where its inaccessible. So once that system has been installed, it is impossible to go back – or very difficult at least – to go back and make changes. Whereas if you have the duct work all coming back to this one central return, just like that PEX manifold, you can pretty easily make changes to the balancing. So we think there is a lot of potential there for improving comfort for homeowners.
Anthony: So where is IBACOS focused on in the future? So, at IBACOS, we are committed to a lot of the focuses that Building America has created for us as an industry to look at. I just put up a slide showing the optimal comfort systems for low load homes road map for the next five years. The outlined areas in red are two areas that we’re committed to look at. One being the development of design procedures and tools, and comfort metrics for low load homes, so a lot of the data and work that Andrew has just shown us is in that area. Then we are looking at validating and demonstrating these metrics and these systems for low load homes in the next several years to come.
So, two areas that we are going to continue. The plug and play is an area that we see a lot of opportunity. A lot of opportunity for the industry to get better at. Specifically our production homebuilder partners. They see the value in it. We are committed to accelerating the level of effort to get to a point where we believe we can design a system that is smaller diameter that will effectively maintain comfort in low load homes. Then, we wanted to understand the time and motion study is for a small diameter install vs a traditional. We believe there is a lot of cost savings as well as cycle time savings in the field. So we’re gonna also look at modelling exercise, continuing what we are doing and looking at opportunities for you know home run manifold systems, or potentially remote manifold systems. So we are going to continue that development of small diameter ducts.
And then the second one is we hinted at it, but we are actually gonna be putting together a white paper for Building America looking at a comfort rating method. So similar to the Hers rating method where there is a square of 0 – 100, that rates the home’s energy performance. Going back to that energy efficiency does not equal comfort, we believe the industry does require a comfort metric that could go side by side with the Hers rating and we can get better, give better information to a homeowner and potentially a builder to differentiate their built home, to a homeowner when they are trying to purchase one. So a homeowner can see both scales and say hey, I’ve got a great energy saving home, and wow, I actually have a better comfort rating for this home, than that home across the street. So we are trying to develop a methodology to understanding. And the areas that we are looking into, obviously we are going to look at ASHRAE 55, how does that standard reflect a new metric. We are also looking at the ACCA RS standard. There’s other factors that we have to consider that potentially these current standards don’t touch. So architecturally design, massing of home, how many stories, they are very impactful to maintaining comfort, not just in the home in general but in rooms of the home. Enclosures is very important. I think that as an industry we have done a better job of getting enclosures, but we also have to look at what the impacts of enclosures are to the mechanical systems. So you know enclosures are basically very good right now, they can improve a bit, but I think that the mechanical system to maintain that comfort for those really high end enclosures. Because the capacities of these equipment’s are basically a lot smaller. In some cases 25% of the traditional size. Then the last size is occupant behavior. You saw Andrew talk a little bit about the occupants, they vary from house to house, neighbor to neighbors. So we need to understand what are the effects of occupancy on creating comfort conditions, so that’s what IBACOS is focused on, at least for the next three years. Any feedback that we can get from the industry, and anyone listening to this webinar, we’d be more than happy to listen to you guys, because that could help us get a better understanding of what we need to do.
Andrew: Thanks again for listening everybody. I guess this point we will open it up to any questions.
Nicole: Alright, thank you so much for that, so we have a whole lot of questions and we are not going to be able to get to them all. So if we can’t get to your question, we will try to address that over email after the webinar.
So going back to the basics for thermal comfort section of the slides, we have a couple of questions there. Someone was wondering do you consider having more humidity adds to discomfort at the lesser temperature difference? The home humidity is high, temperature difference is felt more by the occupant, vs low humidity and temperature difference not be helped. Is that a consideration?
Andrew: Yeah, I mean that might be a possibility. That’s not something we were specifically looking at in this study, that’s getting into pretty detailed levels of analyses to see is it 80% humidity, the temperature bend should be 2 degrees or something whereas at 50% humidity the temperature bend should be 3 degrees. That might be the case, it’s just not something we were really looking at.
Nicole: Ok, great. There were a couple questions on whether there was mechanical ventilation provided in those projects. Exhaust, or?
Andrew: Yeah, and so in that case, they were looking at a total of 4 different homebuilders. Each one used a slightly different strategy. There was mechanical ventilation provided in those cases.
Nicole: Ok, great. And then do you have an explanation for the low RH in homes 3 and 12 in the humidity plot?
Andrew: Yeah, I mean I can try to flip back there real quick, let me just zip all the way back. So you know in terms of specific homes, there are many different factors that could have been causing that, we are looking at homes 3 and 12, so the significantly lower humidity, we don’t have specific reasons, we could make guesses. I don’t have all of the various differences between the homes displayed here for us, but it could have been perhaps differences in ventilation strategies or something. Again, we don’t know specifically.
Nicole. Ok, great. Move on to the comparative modeling section. Someone said your statements on all of the homes measured were able to maintain an RH of 60% without dehumidification is this due to the fact that these homes are using AC during the measurement period?
Andrew: Yeah, so the homes were all using AC during the measurement period. Again, when we are looking at this there were two homes that perhaps there was a humidity concern, we were making some guesses as to why that might be. All of these homes were using air conditioning throughout this process. We measured one of the supply ducts. We put a temperature sensor in that supply duct. So we could see when that system kicked on. There were a few periods perhaps of vacation and I know for example, this home 28, we see that magenta region, that was actually a period of vacation when the system wasn’t running as much. Otherwise these systems were running.
Nicole: Ok, great. We have a question about how do the mini split heat pumps do with respect to humidity? The question asker is from Nebraska, where they see a lot of oversized pipe installation.
Andrew: Yeah, so I guess this is perhaps considering the comparative modeling study and humidity wasn’t something that we were really digging into. I’ve heard also mixed results that oversizing those mini splits might potentially have impacts to the humidity in those homes. Again, that’s not something that we were specifically looking at in this study.
Nicole: Ok, great. And then, one more question about the comparative modeling, someone was wondering was the basement finished, and what was the duct work like in the basement?
Andrew: Yeah, so the basement in that case was assumed to be a finished basement and there was supplied air going to that basement. I have included in these plots, just the only so much space, but those were conditioned basements, and actually the data from that is included in this room to thermostat comparative analysis.
Nicole: ok, great. Then moving on to the multifamily case study section. Someone noticed that you had insulated the ducts within the conditioned space, and noted that many builders do not insulate duct work inside the envelope. Is this typically done only with the small diameter systems?
Anthony: Yeah, so in a high velocity duct system, typically the air temperature is a lot colder. Some of the concerns from the manufacturer, is that they want those ducts insulated even though those are in a conditioned space. They are concerned about condensation forming on the duct material itself.
Nicole: Ok, great. We have a question, at the start of the project with air stratification between floors of the home, both small diameter and traditional system use riser ducts which are historically notorious for not being well sealed which can lead to stratification. Was there consideration of building a more well sealed compartmentalized for way of improving comfort?
Andrew: Yeah, and so in this case that’s definitely a real concern. But we were really focusing on the differences in performance of just the air distribution system, the kind of stock, how its installed today. That would be another interesting area I think to explore.
Anthony: But I believe the duct systems were sealed to the best that we can in these homes that we monitored.
Andrew: Yeah, so we have the measured duct leakage in this table. Now I didn’t get into those numbers but you can see the traditional system actually had a pretty low measured air leakage. We are talking 5 CFM at 25 Pascals. Now the small diameter system had actually showed worse air leakage. So around 50 CFM at 25 Pascals. There are a couple reasons for that. That traditional system was installed with mastic, there was more potential to seal that duct work. Whereas as you saw with the small diameter system, these branches are connected with a foam gasket to that trunk. There is no mastic there, so it is possible that you get a little bit more leakage around those various joints. So that was one difference in these ducts.
Anthony: And we always want to see air tight duct systems.
Nicole: Ok, great. We had a couple questions about noise difference or draftiness when you are looking at the home run manifold system. One person said that fast moving air is one of the chief sources of occupant comfort complaints in office buildings and how do we avoid repeating the mistakes made in that sector. And we had another question about whether there is a noticeable noise difference or draftiness with the system.
Andrew: Ok, yes, so I think I’ll answer the noise question first. That’s something we were concerned with as well. You are putting this rigid ductwork in, are we going to get significantly more noise? So far we have only conducted tests in our warehouse and we basically weren’t able to hear the ducts above just the background noise of various other equipment in our warehouse. We tried to put that meter up there about 3 feet away and we didn’t actually measure any noise. One of our next stages with this project is to install that system in a house in one of our test houses and we will be looking at noise performance. So in that isolated case, we will be able to get better numbers, but our initial thoughts are that the noise performance isn’t going to be a major detractor to the system.
Anthony: Yeah, I would say that the only noise issues potentially is potentially at that actually air handler. Especially if we are building up little bit more static, we may get a little bit more noise from the fan. But as of today, we haven’t seen any increased noise levels from the termination of the duct.
Andrew: Yup. So the other question was related to air flow and you know draftiness and if the air flow was actually hitting a person, or hitting an occupant, so yeah, they might perceive that as being uncomfortable. That’s definitely a risk with these smaller systems that are emitting more of a jet type air flow. I think that that’s an area that is definitely ripe for more study and whenever you are designing one of these systems you do have to be very careful with where you place those registers, so that you are not blowing into potentially occupied space.
Anthony: Yeah, and as you can see in this picture, we are always trying to locate these diffusers as close to the ceiling as possible. So, high side wall, is the best location for distributing air in a room. So you are going to get that effect of throwing air across the ceiling, mixing better, and it won’t be in at someone’s face.
Andrew: Yeah, so the idea is you are probably not going to use for example a floor register or a lower wall register as much as possible. These high side wall registers.
Nicole: Ok, great. Thank you very much. I think that that is all the questions we have time for right now, like I said we will try to address some additional ones offline. We now would like to ask our audience to answer a couple short questions about today’s webinar. Your feedback will help us know what we are doing well and what we can improve.
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