Concerning the Air-tight House

I was just reading the November issue of Fine Homebuilding, and noticed that the issue of air-tight housing came up. Again, as it does ever few years, when the customers get antsy about heating bills and try to cut air filtration to zero.
They invariable discover that a tightly sealed house must have particular attention to the ventilation, and usually must have a air-air heat exchanger capable of handling at one full change of air per hour.
This problem first came up with the first super-insulated houses built back in the seventies, and has been with us ever since. You simply cannot wing it with HVAC without risking a badly sized system.
Replies
capable of handling at one full change of air per hour.
Are you saying that a house needs to have one complete change of air and hour to be considered healthy?
And of course, welcome to Breaktime
A great place for Information, Comraderie, and a sucker punch.
Remodeling Contractor just outside the Glass City.
Quittin' Time
Edited 1/14/2006 3:58 pm ET by calvin
That's a crazily high exchange rate.ASHRAE standard is .35 ACH or a piecemeal method by occupancy/room types, whichever is higher.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
NRT, that's what came to my mind. Hells bells, might as well live outside.A great place for Information, Comraderie, and a sucker punch.
Remodeling Contractor just outside the Glass City.
Quittin' Time
He might consider buying a tent. A joke but not entirely too far out.Actually one air change an hours may be a decent capability, but only as a capability. I wouldn't want it to be on all the time unless you really like the breeze. I helped wire a large home that had a very highly engineered ventilation system. They had the capability to change the air several times several times an hour. Come back after the house has been idle for a month and flip the ventilation system to high. Also useful when the grits gets left on the burner and becomes a science lesson on carbonization. (Silly spell checker put in canonisation. A sauce pan of burner grits as pope. Hmmm. An idea not entirely without merit.)A useful ability but one that need not be used all the time.
Edited 1/14/2006 7:35 pm ET by 4Lorn1
I am old school. Number of air changes: air infiltration + number of times the door is opened x 2 cats and a dog . Don't burn the grits but know when it's time to eat.A great place for Information, Comraderie, and a sucker punch.
Remodeling Contractor just outside the Glass City.
Quittin' Time
Yeah, that'd be nuts. It needs to be a function of the occupants of the house and the size of the house, too. Not to make myself an example, but....consider my example! :) All elec, no gas (appliances, that is), 3 occupants out of the house more than in, and about 100,000 cu ft. I don't want anything close to 1 ACH!
You'd probably know something about this. I realize the exterior air is warmed by the exhausted interior air in a heat recov. system. In the summer, is the air also "cooled" by the exhausted air? How about the humidity in that ext. air? And, is there condensation to take care of in the exhange on the metal ductwork?A great place for Information, Comraderie, and a sucker punch.
Remodeling Contractor just outside the Glass City.
Quittin' Time
Did a bit of searching around, be/c I don't have an HRV/ERV and those I've known of have been pretty simple and primarily used to avoid stale interior air. Others here might be able to enlighten on the latest and greatest brands and capabilities.Here's some of what I found:"ERV: A means by which a mechanical heating and air conditioning unit is capable of assisting in the introduction of fresh air into a building and removing old air, while keeping the temperature consistent inside, with a minimum expenditure of energy. ERV is also referred to as heat recovery ventilation or HRV. Both mechanical processes have a core unit heat exchanger that causes the thermal energy (heat) to flow between two air streams. Some manufacturers incorporate an enthalpic exchanger, so that moisture can be exchanged as well, keeping buildings comfortable in summer, winter and during humid months."Most brands talk about reducing interior humidity, but only in winter. That tells me there's no active humidity control on these--it's hard to find specs for most--and that they're just replacing the more humid interior air with less humid exterior air. It's one of the reasons I like my dehumidifier, be/c I want consistent humidity levels throughout the year, and not just lower in winter and higher in summer.I also saw reference to condensation drains, so I imagine that must be dealt with, but others may have better and more recent info on this. My focus is more on filtering exterior pollutants and humidity control than on temperature control through air exchange, though it's fine if all can happen at once.
Thanks. If I ever go that route I will do some further study, but it's good to know there are varying degrees of recovery with a couple of the questions I had, that have been addressed.A great place for Information, Comraderie, and a sucker punch.
Remodeling Contractor just outside the Glass City.
Quittin' Time
I don't have an HRV/ERV ...
Yea, me too. The ASHRE ventilation codes are a reaction to public perception, a handfull of documented indoor air quality illnesses (primarily due to oversized HVAC, not undersized ventilation) and compensation for poor HVAC design using old school science in new school design. It's unbelievable how much the cost of HVAC, and the energy consumed, has gone up in the last two years on every one of our projects. Quadruple the required AC tonnage is pretty common.
It's my belief that the high outdoor air change rates actually make for less healthy environments. They certainly don't help with the energy bill. Our 2,400 S.F. SIP home, with 3 1/2" tons of air and no HRV/ERV is the most pleasant environment I've ever lived in. Nothing stale or unhealthy about it. Strong cooking odors don't even linger for more than 15 minutes or so.
Now that little 300 S.F. moldy cabin we lived in while we were building was another story. With huge single pane windows and daylight gaps around the door, it provided all the natural ventilation one could ask for. When you can't keep the dust off the shelves in a 300 S.F. space for more than 15 minutes it's got to be healthy right? As small as that place was it took two wall/window units to keep it livably cool (not pleasant but livable) in the summer.
Believe it or not, our energy and doctors bills both dropped significantly when we moved into the new house. Go figure... We've never been as consistently sick in our lives as we were for those 2 1/2 years in the cabin. Tight, done right is the answer! HRV/ERV has its place but it's way over used, creating problems as often as it solves them.
Hi Kevin!
Hey Jim - Couldn't stay away forever.
I have to keep checking on Ryan and T.H. and well, it only takes a second to open just one more thread... then a minute or two for a quick response couldn't hurt right?
Ah well, breaks over - back to work...
"...ASHRE ventilation codes are a reaction to public perception, a handfull of documented indoor air quality illnesses.."
"Quadruple the required AC tonnage is pretty common."
I disagree with both of these statements.
Which ASHRAE ventilation code are you talking about? The ASHRAE standards for ventilation are not perfect by any means, they are continually being revised to accomodate new construction techniques and results of other changes, but they also certainly not develeoped in reaction to public opinion.
The average heating and air conditioning required for a given occupancy has remained relatively constant from prior to the oil embargo of 1974 to the present time. There was a temporary reduction during the early to mid 80's as buildings were sealed0-up, over-cooled and under-ventilated. I've seen schools where CCUV's had there outside air louvers blocked-off with cardboard to "save energy". The problems associated with changing the only one part of the building systems were lumped together as "Sick Building Syndrome" or SBS. This was not "a handfull" as you assert, but a commonplace and still very prevalent issue. I get paid to consult on HVAC problems from time to time and most of the problems I see were created in the previously mentioned era.
"..and compensation for poor HVAC design using old school science in new school design..." This is not quite the case. What really happened was a a large number incomplete "improvements were made by unqualified individuals, that went off half-cocked with just enough information to be dangerous. I have seen many such problems over the years, and continue to see many today. A church that was having problems with IAQ had been re-roofed during the late eighties, and during that maintenance, someone added 2" of rigid foam to the roof, "to save energy". Not a bad idea, you would think. The new problem was that the 25 ton cooling load was decreased to 15 tons by the roofer, and they had no clue of the effect of this change. What happened as a result was short cycling of the unit, poor dehumidification, etc., etc..
The fact is, from the late 60's to the present, the loads have changed very little in properly engineered HVAC systems for similar occupancies in similar climates, with the notable exception of the ever growing prevelaence of high density "server rooms". The low levels of ventilation offset the low thermal resistence of the insulations. Now the higher necessary ventilation rates offset the higher thermal resistence of newer materials and methods. You see 4x the tonnage for the same types of buildings in the same climates? I suppose its possible, but not likely.
Tim,
Your last paragraph has me scratching my head. Perhaps I am misreading it?Are you saying that the HVAC loads imposed by homes have not changed much in the last 20+ years? Perhaps this is true in aggregate, but the anecdotal evidence we see here from homeowners that care is that HVAC loads can be reduced dramatically when attention is paid to the local environment, insulation, actual building construction, etc.For example, homes that are built in climates with very variable conditions can benefit a great deal from having thermal mass added to them. That mass then lets them flywheel through the more "spikey" thermal conditions (hot or cold) with aplomb. Similarly, homes can be built to take advantage of wintertime insolation while blocking out the sun in the summer, etc.And this is my biggest beef with the architectual community at the moment. These people love to clad themselves in LEED and other certifications, yet in my mind the LEED buildings I have seen thus far do not qualify as green... simply because they used a non-toxic wood varnish, planted a few flowers, and put in an occupancy sensor or two it is LEED? In my mind, a green building ought to offer state-of-the-art energy conservation first and foremost...I agree with you that building improvements ought to be addrssed holistically, i.e. in the whole instead of just addressing one issue and ignoring the (potentially troublesome) dependent variables. I also believe that the resurgence of energy prices will cause the same painful learning experiences that were gathered in the early 1980s to be repeated. Ultimately, the real trick is to understand the flow of energy and what can be done cost effectively to harness it.
What I'm saying is that the total HVAC load for buildings (my experience is heavily non-residential) with forced and mandated ventilation rates has remained relatively constant because the energy efficiency gains due to better attention to envelope sealing and better insulation, better fenestration and better controls is mostly offset by the increased requirements for ventilation.
Single family residential buildings (i.e. houses) have little or no mandated forced ventilation, (I know what the IMC requires and what ASHRAE recommends, but operable windows "satisfies most residential building codes for ventilation) at the present time. The residential market is experiencing the "new" issues of ventilation versus improved construction that the commercial and institutional market experience 20 years ago. It seems that, with notable exceptions like Joe Listurbek (sp?), that lessons learned by the other industries have gone largely ignored by the housing industry. The failures are for exactly the same reasons, for the most part, partial implementation of improved methods. If you build a house tighter (than previous standards) and do not address the needs of combustion air and exhaust air makeup, ventilation and humidity control, you have substituted one issue for another, and ultimately have made no improvements to the complete "system". Statements like I read here from many of the builders, lead me to believe that things will get worse before they get better. Because of economic pressures, builders will not make different choices until they are forced to do so, either by market forces or by legislation. No blame, just reality. These are business people, and they have to make a profit in the environment that exists.
"In my mind, a green building ought to offer state-of-the-art energy conservation first and foremost..." You mention Architects only. As with any complex project, such as commercial building, ALL trades must be involved. The good part of this emerging trend is that in the best examples, all trades ARE working together and doing so well. Residential construction current trends (big houses, less money!) are not there yet.
The company that I work for, sells HVAC equipment, and a great deal of that is low dollar, and low efficiency. The new requirement that all residential AC units be 13 SEER, is anattempt at improving the situation, but the law is a partial solution. It is a start, but 90% of the new homes built for the masses (not high dollar custom homes) have 80% AFUE gas furnaces and 0.60 energy factor gas water heaters. Most of boilers customers ask for are single stage, non-condensing. The sales may be local anomolies, but I doubt it. The day may come when I sell more high efficiency HVAC equipment than the minimum required, and I may see it yet. I'm young, I'll wait and see.
Interesting. I never thought that ventilation would add that much of a load to buildings once you implement an ERV/HRV but perhaps our house is ahead of the curve there. I also agree that Architects are but a part of the reason that buildings are not more energy efficient. First and foremost, if customers demand it, the market will follow!Yet, I like to lay a lot of blame at Architects' feet since passive building features can do so much to improve the overall energy efficiency of a place and yet are implemented so infrequently. Never mind leaving enough room for the insulation, HVAC-trades, etc. to have a fighting chance to seal and condition the envelope efficiently. Our architect seriously expected a 8x8 room to fit an oil boiler, standing IDWH, 4 ton AH, etc. I've seen rooms like that before (an architects house) and my hat's off to the nuclear submarine pipefitters that made it work (with little to no room to spare). A beautiful installation, yet I wonder just how maintainable it will be in the long run. I prefer things out in the open... I too hope that the market demand for high efficiency equipment and homes will blossom.
The ERV/HRVs currently popular in residential use (i.e. Venmar, Lifebreath, Renewaire) have a total efficiency in summer conditions of 30 to 40%, witer efficiencies are more like 60%. In a residence, ventilation adds little to the load in most cases, especially with any sort of recovery.
However, most commercial buildings do not have energy recovery on the ventilation systems. In a great deal of my designs, when "value engineering" (which is neither engineering or a value) was necessary, the ERU (I differentiate an energy recovery unit ERUfrom and energy recovey ventilator ERV or a heat recovery ventilator HRV) was usually the first on the cutting floor. Commercial units, depending on the proper selection by the HVAC engineer, approach 90%.
1 cubic feet per minute of outside air at 95 degrees dry bulb and 78 degrees wet bulb requires 50 btu/hour to condition to inside air summer design conditions. To heat the same 1 cfm from -10 to 75 degrees F, takes 92.2 btu/hour. Given these numbers (at my design conditions) when the ventilation required is significant, it affects the load in a major way.
Interesting. So the summer HRV efficiency is dropped by the smaller delta-T it is encountereing or is the exterior latent heat at fault here? Would an ERV work better?My HRV/ERV has a stated efficiency of 87% at low speed, which is where it's running unless a bathroom is occupied. I'll start to document temperatures in the coming days, so that'll hopefully give me some insight into its operational efficiency.However, most importantly, your post gives me a lot of hope for the commercial side of the business. If the potential energy improvements are truly as dramatic as your numbers suggest, then perhaps the climbing energy prices will convince more building operators to retrofit them. Presumably, this is possible?
The efficiency based on the total heat (sensible and latent) for some of these units is suprisingly low. Primarily due to the latent part of the load, but also due to the low dT. An HRV, by my definition, transfers sensible heat only. An ERV, such as the Renewaire product, transfers sensible at 75 to 80% and latent at 25 to 35 % efficiency. I don't have published data on the other Venmar, Lifebreath, et al, but typically those numbers are published for sensible only, at the best conditions. The best commercial units available have a rotating wheel; some made of a desicant coated plastic, some a desicant coated aluminum. Most manufacturers use the AirX wheel, though SEMCO has a unique 3 angstrom sieve design, and Carnes makes their own wheels using aluminum.
The real or total efficiency determination is based on dry bulb and wet bulb conditions inside and out. Efficiency numbers I quote for commercial applications are manufacturer's data at ARI standard conditions.
The commercial, institutional and industrial sectors have a potential for energy savings in almost all aspects of consumption: process, lighting, cooling, heating and ventilation. However, when one part of the system is evaluated on cost/benefit basis, it seldom seems worth while. What is intangible in the instance of an ERU is that the HVAC system can easily handle the latent load and people are more comfortable, at no increased energy consumption.
Since people costs (salary, benefits, etc) are 80 to 90 % of the operating costs(excluding processes) of large businesses. Of the remaining say 15%, 1/3 of that accounts for lighting. IF 2 to 5% of the operating budget of a corporate headquarters is spent on HVAC and my ERV will save 77% of the cost of 20% of 2-5%(less than one percent of ops $$), is it worth it? Only if coupled with many other savings including the incentives provided by programs like LEED certification tax rebates and the like.
"3 occupants out of the house more than in, and about 100,000 cu ft. I don't want anything close to 1 ACH!"
100,000 CU FT, that's 10,000 sf with 10 ft ceilings, IF you had such a place, 1667 cfm of outside would be least outrageous aspect of the castle. IF this is a non-standard shape then ventilation based on the volume would be inappropriate.
In a house with something resembling "normal" dimensions, say 2500 sf with 8 ft ceilings, then 1 ach is 333 cfm. That would be a lot of outside air for average construction. For an AIR TIGHT home, this would be a reasonable air change, unless you had gone to the extreme of eliminating any material that would offgas or any paint with voc's and had all point sources of vapors, humidity and odors well exhausted. In other words, 1 ach is not an extreme rate for an air tight home.
>IF this is a non-standard shape then ventilation based on the volume would be inappropriate.That would be my house.
Stick to the wet stuff Rob, 1 ach is neither a high ventilation rate, nor is it "crazy". The MINIMUM recommended by ASHRAE of 0.35 ach, (is just that: an old, bare minimum, that is based on construction methods of 30 years ago) or 15 cfm per occupant whichever is greater. Less than 3 times the minimum is not out of line.
Room by room, occupancy based ventilation rates can be used for commercial occupancies, not residential.
I have the updated ASHRAE standard here on my desk from 2004. (62.1-2004).Page 38, Table E-2 "Outdoor Air Requirements for Ventilation of Residential Facilities (Private Dwellings, Single, Multiple"Living areas: .35 ACH but not less than 15 CFM per person (in the notes, occupant loading is first bedroom, two people, one per bedroom after, where higher occupancy is known that should be used instead). This number is the total exchange needed, from which you would SUBTRACT your natural infiltration to get your mechanical exchange rate needed. Says right in the notes, this is normally achieved with natural ventilation and infiltration.Kitchens: 100 cfm intermittant or 25 cfm continuous for installed mechanical exhaust capacity.
Baths are 50 or 20, again for installed mechanical exhaust capacity. .35 ACH is not based on any construction type as it does not refer to the amount of mechanical ventilation needed, just the amount of fresh air needed to maintain a decent IAQ. How you hit that depends on the type of construction of the house.1 ACH, for IAQ purposes, is very, very high. .35 ACH is a minimum, yes. Tripling that for continuous exchange rates is a serious risk for overventilation. I don't know about your area, but up here if I ran 1 ACH all my clients would have nosebleeds for the month of December.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Remember that this is in reference to an "air tight" house.
There is no mention of that in ASHRAE 62, present or past. Provided, adding 1.0 ACH outside air to a single family residence of average construction, which would leak anywhere from 0.1 to 0.4 ach when the wind blows at 15 mph, is more than most competent professionals would recommend. In a house of (to use the IMC language) "unusually tight construction" extra provisions for combustion air, makeup air and ventilation are required. Is 3x minimum, extreme in this case? I don't think so.
I have to say, I was surprised when an editor wrote to me, saying he wanted to include parts of that thread in the magazine and could he edit my words a little.
I was simply thinking about the direction our industry has chosen in response to the challenge(s) of making homes more livable, while at the same time affordable to heat/cool.
I still find it ironic that we are steadfast in our efforts to reduce uncontrolled air movement in the name of reducing demand for energy usage. But we are presently so far down that path that if we have zero energy to pump air in and out and regulate humidity we can not safely live in our houses. Talk about "energy dependence".
I have to say, in spite of all the "building science" I read about, I really don't think the Emporer is wearing any cloths.
But, um, there are sure a heck of a lot of people who depend on all these "advances" in building science to earn their daily bread. I guess that's what it's all about for the vast majority in our society - what's best for them as individuals. So be it. TIPI,TIPI,TIPI!
"But we are presently so far down that path that if we have zero energy to pump air in and out and regulate humidity we can not safely live in our houses. "
That is why we have windows that open.
Spend some time in a house with a good ventilation system vs one without. I can certainly tell the difference.It's not always an easy choice, but really it comes down to one of two situations.You can have the air change rate you need, sometimes, wherever the cracks are, recovering none of the heat, or you can have it where you need it, all the time, and recover the heat. Plus filter it. Plus you're more comfortable throughout the home. Plus it's quieter (if that's a concern).It's a big difference. It may not be a basic require of shelter, but for the price of a couple of light bulbs running, you can exchange quiet a bit of heat while dramatically improving your comfort in your home.As another poster said, if your power is out, you can still open a window. It's not like the house has to be abandoned.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
>I still find it ironic that we are steadfast in our efforts to reduce uncontrolled air movement in the name of reducing demand for energy usage. But we are presently so far down that path that if we have zero energy to pump air in and out and regulate humidity we can not safely live in our houses. Talk about "energy dependence".I think you will just have to take a field trip to Asheville and experience this in person. :) In practice, it just isn't the way you've described it. I'm agreeing with NRTRob on essentially everything...based on living in such a house...in reality it's the most comfortable, most economical, least headache setup I've experienced.
Hear Hear.Our present home energy consumption is several times lower than that of the apartment we lived in before when you adjust for the square footage. The air quality is also better, even though it is a "tight" house. IMO, the urban lengend that older houses with their wild infiltration rates somehow have better IAQ than a properly-vented "tight" house needs to be put to rest.A tight home gives you the opportunity to control the air flows across rooms in ways that older homes can only dream of. Having experienced both, I'll take the "complexity" of a well-built modern home any day over the musty simplicity of the older clunkers I used to live in.ADDED: To me, the added complexity of a right-sized HRV adds almost no complexity to my life and house. It's more like a bathroom fan, really, and one HRV can do the work of three individual bathroom fans. There is nothing wrong with KISS, but I also like my dishwasher, washing machine, wall oven, oil boiler, etc. and the time they allow me to save and enjoy my life.
Edited 2/1/2006 8:18 am ET by Constantin
Amen-
I build airtight homes. I could make more money building leaky homes like I used to, but now that I know how to do it right, going back to the old methods would border on negligence. My blower door test on my own home came in at .038 ACH nat. I live in 4200 conditioned square feet with an average monthly enrgy consumption of 1000 KWh and 10 gallons of propane. I use filtered mechanical ventilation of 50 CFM.
I have a client with a similar home. The four of them live in 5000 square feet. We ventilate at 75 CFM. Their son was sick recently and they wondered if it had to do with indoor air quality. They spent 2100$ to do extensive indoor air quality testing. They discovered that there were virtually no VOCs and only very small amounts of chemicals in the air. The allergen that we have the most problem with here is mold. The mold count was tested in the bedroom that the two boys share, the living room, and the basement. The outdoor mold count was 3600 parts per cubic meter. In the bedroom the count was 210 ppm. In the living room it was 113 ppm and in the basement playroom it was 13 ppm. The higher count in the bedroom was caused by the mold spores that they brought in from outdoors on their clothes and skin.
These results put to rest the notion of the outdoor air being fresh. In our climate, outside is where the allergens are. If you control the air, you can treat it. Most houses are overventilated but not with filtered air. When you let uncontrolled air leak into a building, you will sometimes be bringing in toxins, mold, excessive humidity, or excessively dry air. Control the building enclosure and you will make it possible to provide consistently good IAQ for the least amount of energy expended. Our IAQ and energy consumption results prove this beyond a doubt.
Ray,Why do you think people have trouble believing this? I've read things here about how a tight house is akin to an artificial environment like an Intel clean room. Or the extra amount of work it takes. Obviously, those of us who've lived in such a house know that's as far from the truth as can be. There seems to be a PR problem.You mentioned a $2100 IAQ test. Have you found any less costly ways of testing IAQ? Affordable meters?Jim
Well, I do have to say I am not a proponent of (what I think is) excessive focus on scrubbing air, or anti bacterial soaps and other "mega clean" technologies. I do think it's important to have some exposure to this stuff on a regular basis. I guess I think my time as a farmboy as a kid did a lot to give me the immune system I have.That said, running the air through a coarse filter on its way into the house doesn't remove a whole lot of stuff, but it removes some of the bigger nasties. But if you're talking about, say, recirculated HEPA scrubbing, I'd save that sort of measure only for those with severe allergy problems already.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Rob, I meant that people's misperception is that having clean air in a tight house is akin to living in a silicon factory clean room. Obviously, that not what it's like.
Sure thing, just expounding on it a bit. Some people do try to take it too far i think and may contribute to that misperception.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
You're missing the point of the standard. .35 ACH is what is needed for healthy air quality. It makes no difference what the house is made of, that's how much fresh air you need in a typical application. In a leaky house, you don't need a ventilation unit to make that happen necessarily. In a tight house, then you do (but even then, you may not need to provide the whole .35 ACH, as there is usually still some infiltration).So the standard doesn't address how to achieve the air change rate you need, it only addresses the targe ACH rate, which is far less than 1.If you have additional air quality concerns you can't mitigate with a .35 ACH, then you need other stuff (humidifier, dehumidifier, intermittant exhaust, make up air, what have you).Throwing a 1 ACH is quite a significant source of heat loss in a colder climate, or gain in the summer in a hot climate. In a standard built home with a .5 ACH, infiltration may be a third of the overall heat load. Now you want to relaim 60% of that and double it? Why? Put the makeup air needed where it needs to go, and provide for appropriate continuous exchange for regular air quality assurance. Leave some boost capability for high-rate, intermittant needs.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
I disagree with your opinion of what the "point" of the standard is.
".35 ACH is what is needed for healthy air quality" This is not always a true statement.
"..the standard doesn't address how to achieve the air change rate you need, it only addresses the targe ACH rate..."
This is a very loose interpetation, one that is not backed up by ASHRAE interpretations on record and many similar rulings on the IMC, which is based on the ASHRAE standard. This standard and every other prescriptive Code to which I've designed systems, do not allow you to take credit for faulty building construction in allowing lesser than specified ventilation rates to be provided. It is not a target, nor is it open to interpretation. It is a minimum mechanical ventilation rate that must be provided. If you know any competent mechanical PE's at your company, ask one, maybe they can help out on this one.
As a matter of reality, most residential building codes reference neither the ASHRAE Standard or the International Mechanical Code, so this discussion is a mute point.
So the standard specifically states that the air change rate is "normally met by infiltration and natural ventilation", but my interpetation is loose? Hey, if I'm wrong there, feel free to point me to the decisions on record. I'm open to that. But the language of the standard seems pretty clear. I'm not a PE though, so it's certainly possible I'm missing some secret PE code in that language.If other codes are in effect for a particular home then I'll design to their requirements. In my experience though, most of them are prescribing serious over ventilation. ASHRAE has been revising their standard for twenty years now, and each time, it gets lower and lower, and I have a feeling most of these other codes are based on old models (ASHRAE's or not). Of course the constant revision of ASHRAE's also calls theirs into question, but at least their revisions have been in a fairly consistent direction.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
The ASHRAE standard is not Code, and the PE would know that the applicable Code is the law. The ASHRAE Standard is not. The PE would also know, that few if any Code officials (or AHJ authority having jurisdiction) will accept any inleakage towards meeting minimum requirements. Natural ventilation is applicable in some residential buildings, but not always. This was the point of my reference to the Professional Engineer. Our jobs, and responsibility that comes with the stamp, is to ensure that designs meet the Code as written (or provide an Engineering evaluation of an alterantive approach). Justifications based on logic as you are using, seldom receive acceptance from a savvy code official.
Your quotation of the "normally met by" passage does not apply here, though, does it, as we are discussing an "air tight" house. So in that respect, your interpretation is not "loose" it is simply not applicable and therefore wrong. The language in the standard IS clear and clearly doesn't apply. There is no secret that the PE posseses that you do not, other than experience with the pitfalls that can result by concentrating only on the portions of the document that make your case at the exclusion of all others, that and the ability to tell the difference.
I noted already that if other codes are in effect I use them. Believe it or not, lots of areas still don't have formal codes for this sort of thing, in which case I feel quite comfortable with the ASHRAE standard. Even an air tight house has some air leakage, but whether you factor it in or not (and the beauty is, the standard still applies since it isn't addressing installed mechanical capacity, just the actual ACH needs of a home), .35 ACH is a very different animal than 1 ACH. 1 ACH on a continuous basis is incredibly wasteful, and counteracts nearly all the efficiency benefit you could have gotten from your envelope tightening. I dunno... maybe you're running multiple exchangers in series or something funky to improve exchange efficiency. I don't have a problem with the equipment being able to hit 1 ACH for intermittant needs. That's excellent. But you can't be serious if you are advocating that kind of exchange on a continuous basis. Unless you've got an exchanger with a real-world high-90's exchange efficiency?-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
NRTRob,
.35 airchanges per hour?
do you actually size it for that or consider things like door usage etc. as well.
I'd think that you'd have to factor that in.
I have a tuck undergarage.. That big 16x8 foot door open really provides a number of air changes. Now the garage portion is sealed of from the house portion (if the interior doors are closed)...
The front doors open to the outside without benefit of an air lock system which the back doors have (the back doors are the normal entry/ exit method)
The problem I have with guildine numbers like thatis application..
In the summer we simply keep windows open.. living on a lake means that it's still comfortable maybe even a bit chilly in the 80's around here. not untill it gets well into the 90's do we seal up things and turn on the A/C That's a relatively rare occasion seldom more than a day or two..
I wish I could figure out a decent number so I can order my air exchanger..
If you really want to know, hire someone with a blower door to test the house for you. Many utilities offer such a service, as does Energystar.gov. Given that we got all our money refunded (along with the rebates and all that), I cannot recommed the program highly enough.
Constantin,
What will the blower door test tell me that I already don't know? Can they figure out how many times the door will be open in a month? and for how long with a blower door? Can they predict the amount of time the house will be shut up due to weather in a year?
I understand the value of a blower door.. it's a wonderful education tool but it still will not give anywhere near an accurite number.
I have a dog and two kids and a wife. Lets see that equals about 14 ACPH with the doors opening, being left open, and the same for the kids bedroom windows. Half the time I find those open even in the winter.
At night I suppose when I police the area and close all the doors and windows that I can find the house tightens up.
The average day yields more than enough ventilation for my case. I live in an older house that leaks like mad I'm sure so others might have different cases for sure.
Stu
>I live in an older house that leaks like mad
Sounds like the plumber with the leaky pipes at home scenario!
splat
I know it.
There's only so much you can do with old work. Wherever I tear into something I upgrade it or correct any shabby work already there.
The mechanic always drives the most dangerous car on the road too!
Stu
My wife loves nothing more than slamming the front and back doors every single time she lets the dog out and then back in. My question: Does the increased velocity of the door increase my ACH numbers at all? How much harder does she have to slam the door to increase our ACH from about 12.3 to 14?
Edited 2/14/2006 3:59 pm by rasher
Just put in a dog door and let the dog do it for you.
garages have their own requirements, which are normally met with infiltration.you can't count on door opening, unless you want to set up door timers ;)if you're opening windows, then you turn off the ventilation, you're just wasting energy.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
NRTRob,
OK we are in agreement with that, it makes no sense at all to how open windows and doors with an eir exchanger operating.. As you say you are just wasting energy..
You know that may be a whole new market.. sensors on doors and windows to turn off the air exchanger when they are open and a timer to kick it back on after they are closed..
I have already read about the use of such sensors in some EU installations. The thinking is, if you open a window, then you obviously do not need cooling or heating in that room. This is particularly relevant in radiant ceiling installations that are designed to cool as well as heat the rooms that they are installed in. Dewpoint sensors go a long way to minimize mold, but they do nothing to prevent an errant door or window from causing all sorts of mischief.
Constantin,
I first read about them when I read the details of the BIll Gates house. However they still remain far too rare for that to be a reasonable solution at the present time..
I visit thousands of new homes every year. In only one case in 15 years did I see anything like that installed.. That was in a 19 million dollar home (that doesn't count the 5 million he spent on the lot) where the owner had every other gadget and whistle. (as you'd walk down a hall the lights would come on automatically in front of you and go out behind you.. )
Since I can't afford to have two $35,000 chandleliers hanging in my garage I think it will be a while before sensors likr that are affordable..
A heat exchanger is affordable though and if I could just figure out an efficent way to calculate it's installation as well as it's use I'd order it today..