Where to spend $$ – insulation/windows or geothermal?
TjHhLpRXCC
| Posted in General Questions on
Building new home and are having debate with a couple builders….would love to hear others’ opinions!
Which would you recommend for spending $$ on first….better windows and insulation to reduce heating/cooling requirements or higher efficiency systems (including geothermal) to reduce costs for meeting the requirements? (Perfect world would obviously mean doing borh, but limited resources ($$) means we’re probably going to have to make choice between options).
Thanks in advance!
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Ductless minisplit heat pumps have a average COP that is nearly the same as most geosource heat pumps, yet the installation cost is just a fraction of what a central geosource heat pump would cost.
More efficiency improvements are happening in the air to air heat pump arena, but the cost of drilling and/or laying geosource coils is not going down. I'm betting on air to air technology to make geosource technology obsolete very soon.
Here's a great thread on the subject:
https://www.greenbuildingadvisor.com/blogs/dept/musings/heating-tight-well-insulated-house?page=1
Interesting....I've never heard of anyone around here going this route. Do you have any good sites for me to visit to find out more details? Thanks!
OOPS! Didn't see the link you posted....will check it out...thanks!!
Dave,
If you investigate the pages of GBA -- there is a lot of material on this website -- you'll find enough information to keep you reading all winter long.
The answer to your question is simple: skip the ground-source heat pump, for the reasons that Kevin mentioned, and focus your attention on improving the thermal envelope of your home.
Anyone who pays attention to these issues realizes that for a single-family house, a ground-source heat pump makes no economic sense compared to the ductless minisplit heat pumps from Asia, which are capable of heating a home when the outdoor air temperature is -17 degrees F.
Whether you have limited resources or not, every house should have: 1. Top envelope seal job and moisture management detailing. 2. Best insulation that you can afford. 3. Best windows that you can afford. Those three will reduce your heating and cooling loads to the max (within you budget), where you can reduce the size of the HVAC system. Hopefully, the HVAC system is designed, installed and commissioned properly.
Martin
What might you recommend using when temps drop below -17?
My planned 3200 sqft total conditioned house is coming in right around 19-21k BTu heating requirements, zone 6 with 7500 HDD. The thought was to do a 2 ton 2 stage water furnace geo unit and desuper. Cost of install after tax credit is about 13,000, and this included HRV and merv filter (all ductwork, etc).
Does ducting the mini splits reduce the efficency?
Jesse,
If your house is well designed, a ductless minisplit will do fine, since the number of hours below -17 degrees F will be few (and fewer each winter). I live in Vermont, but it's been a long time since I've seen -38 degrees F, which happened in the 1980s.
If you're worried, install a couple of inexpensive electric-resistance space heaters to get you through the occasional cold snap. That's a lot cheaper than a $25,000 ground-source heat pump.
After reading info on the minisplit units, one thing that concerns me is the unit either installed on the wall or ceiling....for whatever reason, I just don't know that we want to have those in each room (I realize that this is somewhat "superficial" but the house has to be a blend of what makes sense thermally and what we like aesthetically.) Do any of the manufacturers have "delivery" options that are more "integrated"? I really like the idea of having separate units that can be set at different temps as desired by the occupants of those areas (a consistent battle in our home!).
Dave,
There is such a thing as a ducted minisplit. However, the ducted minisplit units have a lower efficiency than the ductless minisplit units.
Your choice.
Martin
Even though the mini splits eliminate the ducting, HRV ducting would still be required however to at least bathrooms and the kitchen?
A very reliable rule of thumb: in new construction always spend your discretionary $$$ on optimizing the enclosure first. Mechanicals come second. A top of the line bilge pump is only needed if you have a very leaky boat.
Jesse,
The design of the ventilation system should almost always be considered separately from the design of the heating system. If you want an HRV, you'll probably want exhaust ducts from the bathrooms and laundry room (and possibly the kitchen), and ventilation supply ducts to the bedrooms and living room.
Long time ago I ordered a modular house with 2x6 walls and aluminum windows knowing I would replace them in a few years with a better product. And I did, and put in 92% furnace with a electronic filter. I asked them at the factory to seal the bottom of the sole plate with chaulk and tape all the seams in the vapor barrier. And one thing more, after the house was set I put a 1" blue foam board around the perimeter and heavy insulated the spaces between the floor joists at the rim joist. Just alot of sweat equity.... and follow up to make sure others did what they say they would...
just to iterate what has already been said here - on a few ~2500sf projects we've looked at here in the NW, it was less to focus on envelope (and achieve passivhaus) then install GSHP and associated equipment. additionally, achieving passivhaus ensures significant operational (and CO2 emissions) savings over GSHP on annual energy usage.
i definitely prefer to keep things fairly low-tech and simple...
To illuminate the previous comment: insulation is low-tech, whereas mechanical equipment is comparatively high-tech and therefore prone to failure and/or maintenance demands. For new construction it's clearly better to get a high performance thermal enclosure and not rely so much on the mechanical system.
Of course this isn't necessarily simple because those triple pane windows are not exactly low tech and they are prone to failure, at least within the next 25 years or so. Such is life. If you wanted to make green living your highest priority, you'd have to go low tech all the way--build a home using only materials found on-site (or collected via human power). Nothing off a boat from some other continent, nor even a truck from Canada. No way could you meet this goal and still have a thermostat set to 68°.