The Best HVAC system for a foam House
dm65
| Posted in Energy, Heating & Insulation on
Thinking of building a foam house with R30 walls and R50 roof. Was considering Geothermo but not really sure if it’s worth the extra expense. My choices are geo or propane, If any one has installed a system in one of these homes I would like to here what you used and why. This home will be built in northern ohio.
Replies
With the right contractor, you might even consider the KaRo system from naturalcooling.com. It'll heat your house from the ceiling and provide all the sensible cooling as well. You still have to remove latent heat the old fashioned way, but that'll still result in much smaller ducts than with traditional AC systems. However, unless you have a top-notch AC installer who has done this before, I wouldn't necessarily feel comfortable being the local guinea pig.
GSHP's make a lot of sense in areas where most of the electrical power is generated from coal and other non-gas/oil fuel sources. Under those circumstances, they can become very inexpensive to run. However, the local conditions may vary a great deal across the state, so call ahead and find out just what the trends are before you make a decision.
Propane-powered condensing boilers can achieve some stunning efficiencies in homes such as the one you're describing. Also consider passive solar heating and overhangs to maximize solar uptake in the winter and minimize it in the summer. With the right amount of attention to detail you may end up with a house that requires very little supplemental heating and cooling... a large slab would help via the thermal flywheel effect.
Edited 11/27/2005 6:40 pm ET by Constantin
How big is the house, which way do the windows face, what are the overhangs, what are local fuel costs, what type of lot do you have, etc, etc. HVAC is part of a comprehensive design that's influenced by many factors, and without much more design data, one can no more advise for or against a GSHP-based system than they can tell you today what color paint to buy, given the proffered information.
Cloud,
sounds like you've had some experience with ground water heat pumps. What luck have you had with dependability/repair over time. The reason I ask, I used quite a few systems back in the mid to late eighties. We had at least a dozen custom homes built that had either open loop or closed horizontal loop installations. I had an open loop system installed in my own home and had great luck with it, but only lived there for three years. The overall track record of these systems wasn't so great, however. Hydroheat was the brand unit, and I had customers within just a few years, pulling them out and installing gas forced air. Bad compressors was one problem, along with other breakdowns. If a customer didn't catch the problem quickly, they'd get surprised by a $800 monthly electric bill in the middle of winter, from the backup resistance unit running non-stop all month. I would hope the reliability has improved with the years. I also realize this was when the first residential units were really starting to take off and the bugs weren't fully worked out.
Kind of put a damper on my promoting them since. I'm usually suggesting radiant with hi-efficiency boilers to my house customers nowadays, but still like the idea of the heat pumps if they're more dependable.
In 5 years running the GSHP, I've had two service calls. On one, the compressor was replaced under warranty. On the other, we bled the air from the loop. It's expected that when first filling the loop with water, there will be lots of air bubbles that over time find any high spot and create some gurgling and inefficient operation. We do have an expansion tank and auto-refill, but some built up in the pump and we bled those and added more glycol just as routine maintenance.We also disabled the backup heat strip after calculating its cost/benefit. We also adjusted the set point lower, from 112 to 105, and got _better_ performance.The system is a closed vertical loop, and has performed beyond it's rated btu/h capacity.We've been completely happy with ours, especially be/c the alternatives were less desirable...no good place for a propane tank, etc.
I'm curious what brand system you've got. I have'nt kept up with the brand names out there today, but i would be interested in using the systems again if a reliable company was available. Part of the problem with the Hydroheat company was it changed hands a couple times and warranty issues were a nightmare.
Florida Heat Pump. I doubt it's better or worse than several others.
DM - see http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=66280.22
W/ R30 and R50, you will be "super insulated", extreme homes in this category can be heated with one $15 Walmart space heater (I've heard), and stay ahead of the GSHP amortization for years.
The question is one of heat loss and solar gain- do the calcs (there are programs available online) and some "what if" scenarios, multiply by the c.o.p. of the geo unit vs. propane, and figure how long it will take to pay the difference in your climate. My gut feel is that you will not need geo, especially when you figure in installation costs, potential repairs (complexity) etc. Look for a program that handles ICFs & other building systems (yours) that eliminate air infiltration.
The unknown factors are the future cost of electric vs fuel, and you need to figure in an AC system w/propane, whereas geo will do both summer & winter.
The conventional wisdom seems to be that $ is better spent on great insulation vs. expensive heating systems - I'd agree - its good to see folks looking to build better - good luck!
I want to thank everyone for the quick respoce I have recieved from this posting.
The home we are looking to build is around 3300 sq/ft with most of the large windows to the south. were building on a 5 acre lot with 2 acres of woods behind us, the home will sit in the unwooded section with no trees around. I agree I will have to some homework on heat loads and energy cost once I have acurrate data to work with, but I have been hearing people say that with these ICF or the foam style houses the GSHP syestems just arn't worth the money due to the length of time it takes for the payback.
I was thinking of going forced air with a VAV zoning setup instead of the GSHP. I know honneywell use to make a residential system are their any other manufactures out there that you guys like for residential zoning. I would like to believe that if these houses are as thight and well insulated as they say, then good zoning of a HVAC system and proper total house ventilation would be the way to go.
I have many years experiece with steam, chilled water and DX cooling, VAV, hotwater but it is all in commercial application. The residential side is something I'm trying to educate myself on before I build this house.
>I have been hearing people say that with these ICF or the foam style houses the GSHP syestems just arn't worth the money due to the length of time it takes for the payback.Again, that's like a mixed metaphor...the separate parts don't connect. No matter how a house is constructed, you need to do a load calculation to know how many btu/h are required to maintain a desired temperature. Separately, you need to look at the cost of providing those btu via the different alternatives. And then pick the best combo. The type of insulation does not dictate or preclude any one type of hvac system. The LOAD requirement compared to system costs does that. Now, it's entirely possible that a small, tight house will have such a small load that a higher capital cost system will not have payoff. But also, a large foam-insulated house--say 6000 sf in a northern or mountain climate, just to pick something arbitrary--could still have a large enough load requirement to yield a payoff.It's not the type of insulation that precludes some hvac systems, it's the numbers.
I agree with you that you must know the load befor you can make an intelligent decision.
I don't know this for sure this is just something I have been hearing, is compairing apples to apples propane forced air to GSHP the paypack wasn't great enough to warrent the extra cost on equipment and installation.
I by no means have rulled out GSHP, but I would like to know if anyone is zoning the rooms with an automated system and have they found this to be worth the extra cost. Isn't this something one would do with either systems?
Dave
I'll reinforce what some others have said: make sure you have the heat load to justify a GSHP. The cost is too high to not have a reasonable rate of return. You may be able to take the extra $15,000-$20,000 and make the house so tight and superinsulated (R8 windows, basement subslab insulation, high efficiency HRV with timed air exchange or programmable controls, R50-60 attic insulation, better solar design) that all you need is 3-4,000 watts of electric baseboard heat to meet design temperature heat requirements. And baseboard heaters need a lot less maintenance and are much cheaper to buy/service than a GSHP.
I've worked on a house like that in an ~8,000 DD (F) area. It actually overheated at a family reunion of 30 persons with the heat turned off in the week between Xmas and New Years: outdoor temp = -10*C or about 14*F!! They had to open the windows. This house is 40X28 Cape Cod with only 2,500 watts of heat installed and was in FHP in 1986, I believe.
Just for a point of reference - I just purchased a two stage GSHP (Climatemaster) 3 ton for $5500 and the duct work will run another $3500. Have heard very good things -
My quote was in $$ Canadian so take about 15-17% off.
Are these the installed prices for these parts of the system?
How much will the ground loops or well/s cost?
What's the total system installed cost?
The cost is too high to not have a reasonable rate of return
You bring up an excellent point there. Another is the cost of getting the ground contact, too.
In my town, all you need is a standard pier drilling rig--no 'resistant' strata in the first 300' down. Go just two hours west & south around Austin, and you need rock bits to go more than 3' some places, 30' others. Tacking a couple of grand extra on the project for the plumbing does not improve the "buy back."
Occupational hazard of my occupation not being around (sorry Bubba)
Be aware that in some parts of Northern Ohio it can be hard to find good contractors willing to push envelop.
Not impossible, but this is a pretty conservative area when it comes to building technology.
I am building an ICF house with SIP roof and looked at GSHP systems. As CloudHidden indicated, GSHPs are more efficient at lower operating temperatures; which is great for hydronic heating but lousy for domestic hot water. As the heating requirement for the house becomes a smaller percentage of your heat requirement, the lower efficiency for DHW can kill the gains. It did not work out in my application as DHW is a much larger energy consumer than space heating and I will not need AC/cooling.
I had Richard Rue of Energy Wise Structures model the house. He specializes in analysis of these types of structures all over the country and has made adjustments to his computer model based on actual performance results. I even sent him five years of weather data collected by a close neighbor's weather station, which was surprisingly different from the overall average heating days indicated by ASHARE for this area.
Since DHW is my biggest consumer, I am installing a waste water heat recovery system from GFX Technology: http://www.gfxtechnology.com/. The smallest propane fired Munchkin boiler will be installed, which is way bigger than the required. Cycle times will be OK since there is a large thermal mass in the floor and a large indirect fired water heater.
The moral of the story is you can't base decisions on rules of thumb or shared experience when you build super tight and insulated houses. The whole thing has to be analyzed as a system or you could seriously compromise the overall efficiency and potential savings.
CJD
Being new to this forum I'm not sure if it is proper for us to continue discussing my questions here. Please feel free to email direct if this is the case.
I would love to here more about your choices of products and what you have learned with your reseach.
I have been unable to find good information about ICF an I really don't know what SIP roof is. I have found a few people in this area that have built the steel/foam homes by ewsohio.com. Is this company connected to your energy wise structures?
Be careful of the high efficiency claims of the GFX and others. All I have been able to find is their info and "testimonials" from happy homeowners. Where is the large scale residential study by an independent energy consultant not paid by them??
If you look at the website you posted and go to the Canadian commercial installations, you will see a list of dormatories/barracks and dishwashing installations where the time of use and drainage are simultaneous. This only happens with showers in houses and there aren't that many compared to barracks/dormatories where the bulk of hot water use is showers. The recovered heat could be substantial in these commercial applications but it ain't home!! And they may be implying that this will happen at home also......I don't think so!!
If you don't insulate the outside of the GFX, it's also heating the water from house heat....does this count? Depending on how they get their #'s, there may be an efficiency claimed that is "apparent" as is the case with HRV manufacturers.
HUH!!! Apparent efficiency??? Yeah! For HRV's, it looks like it's 85 or 91% efficient on the face of it from simple calulations derived by measuring temps at all 4 inlets/outlets at the machine........but some of that temp difference (warmer air at the house side supply air port) is created by the heat from the fan motors. We paid for that heat in electric costs so that's not true efficiency!!
The true or "sensible efficiency" is measured right at the inlets/outlets at the core/heat pipes/heat wheel where the heat exchange occurs. In Canada's R2000 system, all HRV's had to be tested and rated by an independent lab before they were allowed into the program. In the manufacturer's spec sheets both the apparent and sensible efficiencies had to be listed.
That has all changed now as I bought an HRV today to install in a friends place tomorrow. Before we chose one, I looked at the spec sheets on the web.....no sensible efficiencies, only the apparent and misleading ones!!! A lot of "smoke and mirrors" in the energy game. I have a list of about 65-70 popular energy misconceptions that I'm developing now (when I have time)
I agree that you can get tremendous variations in efficiency with a GFX. It depends a great deal on the installation. However, it is nothing more than a simple heat exchanger. There are times when average efficiency could be a third of their claims, which is fine with me. In this particular case, it will still yield a better return on investment than a GSHP. There are a lot of cases where GSHPs are an excellent choice, but I would not have known if I depended on the conventional calculations and models used by the vast majority of HVAC contractors.
I also agree that you need to look at the HRV as a total system, which includes the power to run it and the net heat gain the motor produces. It also has to be properly sized and ducted. Most of all, the house has to be tight enough to need one in the first place. You won't know without a blower door test and repairing any of the leaks it may find.
My wife and I had a GSHP installed in a modular home we had built ,R 21 walls R 50 cielings, heating and cooling just shy of 3,000 sq. ft. the highest heat bill we had was $37.00. It was a 3 ton unit. Trane was the make. The 7 years we lived there we never had any problems with it. Our only complaint was because it ran quite frequently it seemed to kick out alot of dust. I am not sure if it is because of the unit itself or because of the install (contractor panned in floor and wall cavities using them as duct work, that could of been the source of the dust). Also, because it is a heat pump it didn't seem like the air felt that warm coming out of the ducts as compared to a gas furnace. But the heating bills were very reasonable. Our climate has 6600 heating degree days (central Iowa region).