Is Building Science really energy efficient?
I am in zone 4a
I have been reading about building science for a while and have incorporated much I have learned into my build; however, a question that recently hit me: Is Building Science really energy efficient?
We eliminate so much of the air leaking, yet, with our ERV running 24/7 and make-up air we are countering that action. The additional air coming in requires dehumidification to boot.
The other benefits aside, is energy efficiency a worthwhile motivation?
It does not seem like the electric bills are going to be impacted that much, unless comparing to a house with truly massive leaking.
What got me thinking about this was the house YouTube Building Science Contractor Matt Risinger built for his family. The energy savings over the poorly built house he had been living in for years across the street did not amount to enough to get an ROI for a mighty long time. I don’t remember his exact differences in SQ FT, or percentage, but his comment in the video was even his recognizing the bill was not much savings.
Thanks for some perspective or links.
-Mike
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Replies
Mike,
Building science is a field of study related to physics. Building science researchers study how moisture and heat move through building assemblies. This knowledge, shared in scientific papers and at scientific conferences, is agnostic on the topic of energy efficiency.
A house with a tight air barrier, ventilated with a well-designed ventilation system, will almost always require less energy to operate than a leaky house built by workers who make no attempts to seal air leaks in the building envelope.
You are correct that the return on investment for some energy saving measures can be very long. That's why critics of the Passive House standard developed the idea of the "pretty good house."
Something that seems to me under-acknowledged is the huge variability in climate conditions in which people live. I happen to live in an area that sees only a few days a year below freezing and a few days a year above 80 degrees. I run neither heating nor cooling at all for at least 6 months of the year and if I need fresh air I open a few windows to get some cross ventilation.
My house has 2' thick stone walls with little to no insulation in them. The roofs have insulation to about R20 at best. I could probably upgrade the roof insulation and see a reasonable if long payback.
My windows are single paned but with beautiful chestnut frames and jambs that are in perfect condition after 120 years. Once a year the local PVC window company salesman knocks on my door and I politely tell him to go fly a kite.
If we really want to deal effectively with residential energy usage we probably need to do 2 things, reduce human population by half, and all move to more temperate climates.
It's ironic that building codes would prevent me from building a house like this today. With uninsulated locally sourced stone walls and a slate roof it probably has less embodied carbon than most wood framed houses with concrete basements and framing materials shipped many hundreds of miles. And given my minimal usage of heating (and no cooling) I've got no need for large quantities of petrochemical insulation.
I would argue that overall the greenest way to live is at high density. Regardless of climate we should be living in cities, preferably in multi-family dwellings.
Interesting perspective. Shipping your food hundreds or thousands of miles and then shipping fertilizer to those fields maybe across the ocean to make up for the fertilizer being shipped to cities in the form of food.
Then the cities create massive pollution problems by the sewage pumping the nutrients from the food into the environment.
I can think of no worse way to care for the environment than to live in densely packed environments.
As someone who has lived in rural America for half my life I agree with the Contrarian. The town I just moved out of has nearly zero industry, yet you can't drive a quarter mile without passing a few mailboxes. We're talking thousands upon thousands of people in a three town circle that are almost all DRIVING big trucks 40 miles per day to go to the closest "big" city for work. All of that daily driving more than goes over the shipping of food. Personally I think only farmers should legally be allowed to purchase land over five acres in size, and all the run down towns like North, South Carolina need to be bulldozed and reverted to regenerative agriculture. Don't even get me started that all these people want pristine lawns on their lots, which is more fossil fuels getting burns regularly.
"Personally I think only farmers should legally be allowed to purchase land over five acres in size"
Who'll own the forested lands then?
maine_tyler: forested lands should be owned and maintained by the state.
It would probably be sufficient to curtail the subsidies to rural living -- universal service, rural electrification, federal grants for roads, schools and the like. Most of rural America would be uninhabitable without government subsidies.
Go into a supermarket in a rural area and ask them where they get their bananas. Or seafood. Even food that might have been grown nearby was probably shipped to a city for processing before being shipped back to the rural area.
But the reality is shipping is only a small part of the energy use in growing food. People in cities use far less energy for transportation and for heating and cooling.
And centralized treatment is far more effective for dealing with sewage. In my city, Washington DC, drinking water is taken out of the Potomac River upstream of the city. The ensuing sewage is treated, the nutrients and pollutants are removed and the water is discharged downstream. The discharge water is cleaner than the intake water was! The nutrients are captured and sold to farmers. This is far better than every household having a septic system. One of the reasons the upstream water is polluted is that there are so many septic systems in rural areas that do a poor job of waste treatment and their pollutants end up in the river.
"Shipping your food hundreds or thousands of miles and then shipping fertilizer"
dpilot, do you really live in a place where all or most of your food is coming from nearby? There are certainly areas of the country that are agricultural hotbeds, but even then they don't tend to carry the variety needed.
Someone could, with great effort, attempt to be very 'off-grid' in their food (and other?) consumption methods. Utilizing local land for their heat, shelter, food, etc. It sounds kinda nice, but the reality is that due to economy of scale, and a other issues, that person would likely be utilizing a much larger area of land to sustain themselves than people living in a dense region being fed from the end of supply chains.
I encourage you to take the population of some state, then divide the number of livable (non wetland, etc.) acres of that state by the population. Everyone would have a nice chunk of land to live on. How big is that chunk of land? Is it all good cropland, etc.? Is it enough to totally sustain yourself? Furthermore, there would then be settlements dispersed evenly everywhere--not so great for wildlife. I realize this is an extreme model (the exact opposite of 'density is good') and not necessarily what you are advocating for, but it is illuminating nonetheless.
I say all this as someone who lives in a rural area (yeah we don't all practice what we preach), but I try to be honest about the logic of it.
I model most of my projects in BEopt to fine-tune the building components. I usually find that going with Pretty Good House-recommended levels of insulation and air-sealing, and the equipment required, adds a few percent onto the cost of the home with return-on-investment in the 5-10% range. That's not the most amazing ROI ever but it's pretty much guaranteed; try finding that with another investment that returns over 2% annually. Mechanical ventilation always comes with a cost to buy, install and operate, but it's simply necessary for a tight house and a bonus is that the indoor air should be cleaner and healthier for you than the outdoor air.
One thing to keep in mind is that the point of HVAC isn't efficiency, it's comfort.
You don't need air conditioning, and you don't need heat beyond what keeps your pipes from freezing. Keeping your house at 40F in the winter and at ambient in the summer uses the least energy, and people lived like that for millennia. Everything beyond that is comfort. Comfort is a combination of temperature, humidity and indoor air quality.
While we don't often explicitly discuss comfort, we spend a lot of time here talking about how to achieve an acceptable level of comfort while minimizing costs, both ongoing operational cost and capital cost. When you look at capital cost you have to look at both what something costs and how long it lasts. Those subjects are never far from mind.
Some building science relates to longevity of the structure too, not just energy efficiency. Efforts at improving moisture tolerance of walls is one example, and if the structure can last two-three times as long, that's a plus for overall energy use of the home too -- it takes a LOT of energy to REBUILD a house after all!
An ERV uses some energy, but not as much as may be lost by a very leaky home. I suppose the optimal point would be a "perfectly leaky" home, leaking JUST ENOUGH to keep indoor conditions under control. I don't think it's realistic to build something like that though, since leaks are uncontrolled even under the best of conditions. With an ERV, you can control the rate of air exchange, with leaks you cannot.
I do agree that local climate conditions don't seem to be considered as much as they should be. Most of the building science concepts discussed on this site, and a lot of what's in the codes, are targeted towards the "frozen North", generally heating-dominated climate zones. That makes sense since more energy goes towards heating than air conditioning generally, but it can be an issue for more Southern climate zones that have different issues, especially in regards to moisture drive. There is too much emphasis on a one-size-fits-all approach I think.
Bill
The problem with the "perfect leaky" home is that infiltration is mostly driven by temperature differences. So if you build a home that has enough ventilation to maintain indoor air quality in typical weather on the coldest and hottest days it's going to be inefficient, drafty and uncomfortable.
It's very much analogous to the challenges with passive solar.
Yes, exactly! You can't make it "perfectly leaky", because you can't control all the variables involved that control the rate of leakage. Thus, leaks are somewhat by definition, uncontrolled. For an energy efficient system, you want to control things as much as possible, which is why HRVs exist and we try to do a good job air sealing structures that are intended to be energy efficient.
Bill
There is still a lot of work to do on domestic efficiency, which should fall under the umbrella of "building science" in my book. We were able to drop our domestic power consumption by about 40% by adding some intelligence to lighting, and examining parasitic/standby power use. Many of us are using LED lighting, but far fewer are using Zigbee (wireless control) lighting. A smart LED bulb that uses 9 watts at full brightness will use about half that if dimmed 50%. Phillips HUE lights, if used with their motion detector allow you to set lighting levels (or hold lights off) based on ambient light conditions in the house. If you apply this across all scenarios in a home, this potentially, reduces power consumption considerable, although adding smart bulbs adds a bit to parasitic load. HUE are expensive lights, but you can do the same with $8 IKEA lights and a motion sensor (usually wireless) with LUX capabilities (quite common now).
In the last commercial project retrofit I GC'd on, we modelled the building for ambient light gain, before cutting a single opening for windows. For interior 2nd floor hallways we used a few Solatubes to bring sunlight into the space and hold lighting off with Wattstopper sensors. The same "dumb" sensors were installed throughout the 9000 square foot building. How many conversations have you seen here on solar light modelling for residential spaces?
The same thing applies to ventilation. Pretty much every ERV/HRV I've seen on the residential side is set to a single speed, and then left running 24/7. There are again potential savings here that we are seeing using 0-10 volt control of EC fans, which themselves are far more efficient than conventional AC motor fans. The system in our home ramps up and down 50, 60, 75 and 90 CFM (or off completely) based on CO2, Radon and VOC levels in the house. None of this is hard to do right now with off the shelf automation bits and the hardware is not crazy expensive either. If we have windows open (often the case where night cooling conditions are present) then the system just ramps down, and potentially turns off. Power use for the system then drops to near zero. At 75 CFM, it's only 45-50 watts.
All of these challenges require an integrated systems approach but once you start taking a more holistic approach to air management, moisture management, air quality, and efficiency, then the potential for ROI go up yet again, without sacrificing comfort or quality. Costs across the board continue to drop for "smart" switches, bulbs, controls and sensors.
I'm still 100% a fan (pun intended) of simple, compact and efficient which sadly describes very few new homes built today. Packing a house full of sensors and controls is not necessarily efficient so my thinking is that our end goal should always drive to simplicity where possible.
This observation comes up more often than I would imagine. Folks wonder how a machine — any machine — running 24/7 can be energy efficient. But a home built to a high-performance standard, that benefits from an ERV in the first place, is likely to be more efficient in every way. The need for heating/cooling is reduced thanks to insulation, the use of hot water is optimised, the HVAC equipment is significantly smaller and monitored by better thermostats, etc.
Smarter people than me have done the math. In terms of kilowatt-hours, yes, a modern home designed with Building Science best practices is much better than the alternative, even with a fresh-air system running. But do home improvement projects, even ones powered by building science, pay for themselves instantly? Of course not.
Just think about this: Your neighbour, with their standard-built tract house, is paying much, much more every month to live in a home that is rapidly being torn apart by moisture, air, mold, bugs, and chemical degradation. You've made better decisions.
Fortunately! A fairly large percentage of the writers commonly contributing
information on this site seem to have some to considerable engineering
background and education/experience.
Unfortunately! A really large percentage of the general public has effectively
none at all and generally displays a total lack of interest if not outright contempt
for discourse revolving around energy efficiency in housing.
Return on Investment talk usually garners a bit more interest (mostly when
they get ready to sell). However, ROI is a relative thing - the ROI of a house built
in Austin, Tx. will be immensely different than for an identical house constructed in
Gunnison, co., or in Phoenix, Az. (all places I have lived). The logical way to analize
ROI is relative to the costs incurred during a specific interval for a standard-built
house compared to the energy efficient house you have built or are considering
in your location. A lot of the individuals who commonly contribute to this site
have enough engineering background and/or experience to perform a reasonably
accurate analysis - most of the rest of our population doesn't.
While such an analysis is easy to perform after living in the energy efficient house
for the specified interval it is nearly impossible to accurately predict in advance.
The complication comes from the inflation rate for energy during the period you
live in the house. I built and lived in super insulated houses between 1972 and 2003,
during that period the price of a gallon regular gas varied between $.30 and $2.30. The
prices of electricity and other heating fuels for housing jumped around by similar
amounts, way up one year, way down the next, no pattern but the trend was always
up. You will not be able to accurately predict your ROI for a given level of energy
efficiency but the smart money is on "Higher is Better"!
Mikeysp,
As Martin said: Like all sciences, Building Science is neutral and just provides data which allows you to know the consequences of an action you are considering. It isn't Building Science telling us to be more efficient or construct things in a certain way, it's people in the field who look at data and suggest ways that might lead to better outcomes. Those suggestions vary widely.
Yeah, I'm thinking instead of building science what he's talking about is 'high performance' building (informed by BS).
I've always felt like 'selling' air tightness to the uninitiated is made difficult by the fact that mechanical ventilation is then needed. You mean, we're gonna spend extra effort to seal this place up, then spend money and effort to install and run an entire extra piece of equipment?! It takes more than a few words to explain the whole rationale behind it.
I've only lived in older houses with no mechanical ventilation. I did add some lunos hrv's to a build but I didn't live with them. There is something about needing extra 'fancy' equipment that doesn't feel green, but that feeling doesn't necessarily reflect the reality of the ROI associated with tight housing / mechanical ventilation.
The most efficient is of course a tight house with no ventilation. So it's as DC says: we add in the extras for comfort.
Just to be clear, "a tight house with no ventilation" would be literally unlivable. It would make its occupants sick. So ventilation in that case is for more than just comfort.
Sure, I guess I shouldn't presume readers won't misinterpret my point seeing as I was a bit loose with language.
My point was that adding ventilation is purely for the occupants and not a means to efficiency. Any iota of ventilation is reducing efficiency (at least when outdoor temps/humidity are less favorable than inside).
Comfort is not the most accurate word, true, but I meant it as a catch all to include other things like 'health,' which I would be happy to argue is a form of comfort.
"would be literally unlivable."
If by no ventilation we mean literally zero air excahnge, yes. But countless houses have zero mechanical ventilation and there is a spectrum amongst these houses as to how tight they are. Plenty of extremely leaky houses can be made 'more tight' without needing to add in mechanical ventilation.
I hope I didn't come off as nitpicky. I was directing my comment at people coming across this thread who might be new to the site and/or unfamiliar with the issues.
As far as "livable" what I mostly had in mind was indoor air pollutants and CO2, not oxygen deprivation. It would basically be an unhealthy environment and have long term negative health consequences.
That said, I'm with you 100% that most older houses can be tightened up considerably without needing mechanical ventilation.
JGSG,
I think your point of clarity was totally fair and useful.
I have really appreciated all the responses. I live in Middle Tennessee, so mold here is HUGE problem with many, many houses and this is no embellishment. My circles are not huge, yet, I can count literally dozens of friends who have had mold problems with their houses. So, I do not regret applying the practices I have learned since discovering BS, as I now know that making a house that will not so easily succumb is very easy, if simple principles are not violated during construction. My pretty good build is almost complete, and we are excited to be moving out of our camper in about a month.
From what I read here, I may at some future point play with some smart technology to control ERV based on exact occupancy.
The technology exists, it's just kind of expensive. Look at the CERV by Build Equinox. It senses indoor air quality and vents only as needed. It senses indoor and outdoor temperature and heats or cools the incoming air as needed. It recovers heat or cooling from the exhaust air.
Others have covered all these points in more detail, but in summary:
-The economic return on investment isn't always there, but can be optimized if you want to do that.
-There are significant durability advantages, especially with regard to moisture management, to some types of 'high performance' building enclosure designs. Air tightness often plays a major role in these designs. Note: it is possible to build an extremely energy efficient house that is not very durable.
-Comfort is a major factor and cannot necessarily be assessed with the lens of ROI. I did not personally buy a toilet with a heated bidet seat because I felt I would come out ahead on toilet paper costs, but it was worth it in terms of comfort.
This post does hit the nail on the head in many respects. For example with the installation of heat pumps there is a bit of savings over natural gas but in reality, the homeowners may be going from heating only 30% of the house during the winter to heating 90% of it. So there is not going to be any savings if you have upgraded your comfort. This comment applies to older homes in northern climates, where many homes built prior to 1960 were set up to have a warm central heating zone and then not bother with distributing the heat in the poorly insulated rooms away from the central heat, which would be wasteful with poor insulation used at the time.
In my view, the incentives are not structured correctly for your typical low to middle income homeowner. You can get a partial rebate for a $150,000 retrofit but if you want to do a $20,000 retrofit there is no program for it, at least here in Massachusetts. So the efficiency programs end up steering a lot of money to the homeowners who are putting in the fancy stuff, or doing things which are marginally effective (adding attic insulation without taking the time and effort to actually fix holes in the building envelope that are concealed by your vinyl siding).
There are exceptions to this... Back in 2013 there was a $750 rebate on heat pump water heaters and we managed to buy one at Lowes for $999. So the installed cost came in at under $700, and it lowered our electric bill a lot.
It would be a good idea for the incentive programs to use bulk purchasing power to procure a lot of $3500 heat pump systems that can be installed for $2500 in smaller homes. It is crazy that a resident with a 1500 square foot house is paying $20 to $25K to upgrade their heating system, before rebate, when the cost of such systems could actually be a lot lower.