$25,000 contest help needed

[Deep River]

Good evening folks,

The new house I am building has been selected to participate in a zero-net-energy type contest. Awards will be based on the lowest as-built HERS index from the REM/Rate program.

Notwithstanding the prize money I'm looking to build the most efficient house that I can, with some reasonable cost constraints. So, given:

- an 1152 s.f. single story house.
- 7500 d.d. New England climate.
- superinsulated (R-40 walls, R-60 roof, R-30 slab on grade, high effficiency windows).
- very tight envelope construction, (<.35 ach).
- solar tempering on conc slab for thermal mass.
- design heat load of 8,400 Btu/hr at -10 deg. f.

What is the most efficient way to heat & ventilate my house?

What system will get me the lowest REM/RAte HERS index??

All your creative ideas and technical explanations are welcome and sought after.

Some possibilities I have explored:

1) Whole house ducted HRV with 2000 watt in-line electric heating element between the HRV and fresh air supplied to the house.

2) Whole house ducted HRV with single direct vented sealed combustion gas furnace (Rinnai 263 or similar)

3) Whole house ducted HRV with a Mitsubishi Mr. Slim heat pump. (Would I still need an electric or gas backup heat with this?)

4) Forget the HRV (and the electricity cost of the continuous fan) , install the absolutely smallest wood stove I can find (Jotul 602, 28,000 Btu/hr max output) and put "smart hole" vents in each of the bedrooms for fresh air. Exhaust moisture from the bathroom and stove with directly vented fans.

Please let me know what you think.

Boatloads of good karma flow to the best solution!!!!

Deep River

[Wolfer]

mmm karma flow.

[firecontrol]

8400 btu's/hr? Did you forget the windows in the heat load calc? At -10°F design and .35 ach you're infitration has to be close to that.

With very tight construction and the design temp you're going to need an HRV or you'll have a brand new energy efficient home that only the mold will be able to live in.

You mentioned solar tempering for the slab. How's is this going to be accomplished?

If I was building it and wanting to keep energy costs to a minimum with that small of a heating load I'd go with a ground loop heat pump. If cost isn't a problem I'd get the best one I could with VS air and staging if available. (I don't deal in them so I'm just thinking outloud on that.)

With the heat pump you can dump the HRV into the ductwork and get your tempering of the incoming air.

Another thing you might want to research is a HP water heater option.

[67Firebird]

Possibly geo-thermal?

[beenthere]

Zoned radiant slab.
<.35 is not that tight.
<.25 is tight.
How do you plan on keeping the humidity down in the winter, just the HRV?

[gonekuku]

1152 Sq ft 8400 BTU at -10F outside? That's nuts...

Assuming the design heat interior temperature is 68F, you need only 107 BTU / h / degree of difference between inside and outside.

Three people sitting down generate about 70W of heat each. At 61F, you could heat the house with three people. Add a fridge, lighting, television, stereo and a computer at an average consumption of 1000W, you are generating 3400 BTU of heat, or maintaining 68F indoors if it's 36F outside.

I don't have an answer to your question about the best heater....but on top of the internal heat generation, you could heat the house with a 4-slice toaster. The toaster could make you the big winner for innovation, efficiency, low installation and maintenance cost.

[DPSwitch]

mmm karma flow.

Does Harris make that? Does it require flux?

[Deep River]

8400 btu's/hr? Did you forget the windows in the heat load calc? At -10°F design and .35 ach you're infitration has to be close to that.

The heat loss calculator I've been using:

http://www.builditsolar.com/Referenc...s/HeatLoss.htm

puts the infiltration load at 4400 btu/hr. Conservatively applying an HRV at 50% efficient yields infiltration load at 2200 btu/hr.

With very tight construction and the design temp you're going to need an HRV or you'll have a brand new energy efficient home that only the mold will be able to live in.

So it seems most everyone would agree that an HRV is an appropriate/necessary ventilation requirement. I've been looking at a Lifebreath 155 ECM. 155 cfm is about .8 ach, so, when on its high setting I ought to be able to remove plenty of air & moisture.

I propose to have a single stale air intake in the bathroom on a timer. Fresh air will enter the house in each of the three bedrooms (balanced to 30cfm each) and one duct into the main room/kitchen (balanced to 65cfm).

Additional kitchen ventilation will exist from a dedicated stove hood, required by code, and used only as needed.

You mentioned solar tempering for the slab. How's is this going to be accomplished?

House is 24'x48', elongated e-w, oriented 6 deg west of true south.

South window area is 90 sf (8% of total floor area) with triple glazed U=.3 and SHGC=.68. A decent passive solar tempering without too much risk of overheating in the summer. Overhangs are well designed for mid-summer shading, but will let in some sun during the shoulder seasons.

If I was building it and wanting to keep energy costs to a minimum with that small of a heating load I'd go with a ground loop heat pump. If cost isn't a problem I'd get the best one I could with VS air and staging if available. (I don't deal in them so I'm just thinking outloud on that.)

With the heat pump you can dump the HRV into the ductwork and get your tempering of the incoming air.

firecontrol, please tell me more about this. Cost is a concern, but not necessarily a problem. I don't quite get "dumping the HRV into the ductwork".

Would an air source heat pump, like a mitsubishi Mr. Slim, work for me when the outdoor temp is 0 deg F??

[Deep River]

Zoned radiant slab.
<.35 is not that tight.
<.25 is tight.
How do you plan on keeping the humidity down in the winter, just the HRV?

Won't really know the ach until we build it and test it. Walls will be double, 12" wide with blown in cellulose. We plan to build the exterior walls & ceiling and then pressure test to find & fix any leaks **before** we blow in the cellulose.

Yes humidity will be managed solely by an HRV with high speed of 155 cfm, around .8 ach.

Do you have any comments or suggestions for me about this?

[Deep River]

1152 Sq ft 8400 BTU at -10F outside? That's nuts...

Yeah, I like it that way !!!

I don't have an answer to your question about the best heater....but on top of the internal heat generation, you could heat the house with a 4-slice toaster. The toaster could make you the big winner for innovation, efficiency, low installation and maintenance cost.

gonekuku, you've got it about right. That's why my preferred option for backup heat is a 2000 watt in-line electric heating element in the HRV!!

While I'm keeping an open mind, the heat-pump ideas (ground loop or air source) all seem like overkill to me. Same goes for the 9000 btu/hr natural gas Rinnai heater.

The passive solar should kick in when it's truly cold, as that usually happens with a high pressure system around here, meaning it will be "clear, sunny & cold".

The backup heat will likely only be needed during extended cloudy periods, when the temperatures will likely be in the teens or 20's at worst.

One thermal model I ran (using actual historic climatic data), indicated that with no heat & no occupants the house would never get colder than 48 def F.

Keep the comments coming folks.

So far I've heard nothing to dissuade me from a basic ducted HRV with a 2000 watt heater. Should I just go ahead with this plan or am I missing something??

Deep River

[housesmart]

Sorry, but the options your considering seem to too conventional to me to win such a contest (although I don't know exactly how tough the competition is, but the winner will probably spend a fortune.) When I think "zero-net-energy " I think of a 5 COP geothermal system (Water Furnace brags they are the first manufacter to introduce such units) which will heat your home all year round at 500% efficiency, which would have a desuperheater to pre-heat your hot water (or maybe solar hot water), and which would be run on electricity generated by solar panels. The result would be zero net energy consumption and zero utility costs on heating, but the $50,000 (very ballpark) investment would still not be recovered within the life of the heating system/solar panels.

Yes, you would require backup with the Mr. Slim. It will have too little heating capacity when the temperature gets several degrees below zero. Luckily, since you are thinking of this now you can get the proper electrical supply to run a heat pump with electric resistance heating.

It sounds like you are going to do your research to get a house that is very energy efficient a reasonable cost, but I bet the contest will be won by a guy who goes crazy buying everything.