A lot of what you are buying with geo is efficiency. So I'd pin them down on expected COP or better yet, annual operating cost (including aux heat) and not worry about loop temps. Of course they won't guarantee it, so there is a danger of exaggerated claims unless you run ground loop software and check manufacturer specs yourself.

What were their quotes?

That 57,000 BTU/hr number sounds high for a new house done well. Go over the Manual J or similar calcs done for the house, looking at every line of the report carefully. When using canned software, it's very easy for even experienced users let the software make incorrect assumptions about things. Air leakage is one big area for error. My own house (central NH, zone 6), although double-framed superinsulated, has about 4,000 sqft (gross) of floor space on two levels, or a few hundred less if you don't count stairwell and wall footprints. Three different geo outfits all came up with heat loss in the mid 50,000 BTU/hr range and called for a 5-ton heat pump. My own spreadsheet heat loss calc showd less than half of any of theirs. One huge difference I saw from the details of one of their calcs was 10,000 BTU/hr for a fireplace (there is none), and another was for a much higher air leakage allowance. Those two together accounted for 80% of the difference between their total and mine. The other 20% was for miscellaneous things pertaining to windows and walls, despite my having provided all the details on that, and even my own spreadsheet!

In the end, I went with my own calcs and ordered a two-ton CM Tranquility 27. Even my own calcs were a bit conservative, as the unit keeps the house at temp in winter, running in just first stage. For summer cooling, it's oversized by a factor of two anyway.

On that radiant floor basement, you ought to put 4" of foam under the slab, not just the commonly used 2". Then again, if the house is indeed very well insulated, you may want to rethink doing radiant. A slab won't feel warm without shoes on unless it's in the upper 70s. In a very well insulated house you can't run a whole floor that warm, or the room gets overheated.

It takes a lot of time and attention to detail to get the heat loss calc done properly for a very well insulated and tight house. Many contractors won't take the time to get it right or don't know how to do it for such a house.

if the house is indeed very well insulated, you may want to rethink doing radiant.

I agree, you might be down to only a few degrees difference in floor temp (between radiant and no radiant) under most conditions (it will be higher on design day).

Regarding the Bosch design, I would avoid the use of a buffer tank (excluding DSH) where the zones (in this case, the basement loop or the air handler) are big enough to absorb the first stage heat pump output. It will only decrease efficiency.

If you stick with radiant, consider pricing a third zone to supply 100% of domestic hot water.

Someone with 40F min entering water in the winter is overengineering and likely it is at your expense. I'm leery of the lack of auxiliary heat in design one.

Posted By jonr on 06 Jul 2013 01:57 PM

if the house is indeed very well insulated, you may want to rethink doing radiant.

I agree, you might be down to only a few degrees difference in floor temp (between radiant and no radiant) under most conditions.

Regarding the Bosch design, I would avoid the use of a buffer tank (excluding DSH) where the zones (in this case, the basement loop and the air handler) are big enough to absorb the first stage heat pump output. It will only decrease efficiency.

If you stick with radiant, consider pricing a third zone to supply 100% of domestic hot water.

Jonr,

A buffer tank will be needed. The load side flow MUST be set up the same as a source side closed loop field. 3GPM/Ton, in this case 18 GPM. I have never seen a residential radiant system that requires 18 GPM for the smallest zone.

Bergy

System 1 Estimated 3.54 COP & 22.9 EER. System 2 I only have the manufacturers specs: Partial Load: 4.3 COP & 25.4 EER. Full Load: 3.8 COP & 18.5 EER. System 1 contractor estimates annual operating costs of $880 (heat $459, cool $47, fan $83, hot water $292). Energy auditor estimates $605 (mainly lower water estimate slightly lower heat & cool estimate). System 2 estimate from the Energy auditor is $562 annual operating cost. I don't have numbers from the contractor.

What would you do for aux heat? The contractor mentioned that most other contractors typically only use 400 ft/ton for their loops. Is there a "sweet spot" for loop size/ ton? I suppose it depends on a lot of different factors.

Can you do forced hot air for the basement too? If well insulated, the comfort will be plenty good. This will simplify the system and yield less parts and require less stuff to fiddle/tune/worry.

Your load is likely much closer to 3 or 4 ton, and you should put all you efforts into verifying this now. Use some resistance to cover the extreme cold days.

Auxiliary heat is what you use if need exceeds system capacity. So if you have loosely a 4 ton load and a 5 ton geo offers about 4 tons of heat in the winter you may exceed system capacity on cold days and need auxiliary heat.

I second what others said about looking into downsizing to <= 4 tons and having it use some electric aux heat. Or adding more insulation and air sealing to the house and going to <= 3 tons. Comparing annual operating costs to purchase price should make the sweet spot clear.

Do most people use electrical strip plenum heaters for Aux heat? I'm now seriously considering skipping the radiant heat in the basement and going with forced air only. It would save ~$10,000 in upfront install cost.

Another new twist: Due to logistics, I might be forced to go with the horizontal boring loop field. I will be the 1st geo system in my town's city limits, and I just found out that my particular neighborhood has a "no well" covenant. It was enacted to force people to use city water/sewer when they first developed the neighborhood 15 yrs ago (Long before anyone was considering Geo). If I want to get the covenant amended, I need to get signed approval from the majority of property owners in the neighborhood PLUS my local city planning/zoning board AND the city council!!! Good times!

Some municipalities have a clause that permits heating and irrigation wells. Also the exclusion is generally against water wells vs vertical closed loop systems.

I'm waiting to hear back from the city planning department about the wells. We'll see.

Probably best not to refer to them as wells (which by most definitions they aren't).

I'm attempting to learn from the experts here. So is the consensus for this gentleman's solution to go with a 4 ton GSHP. an electric strip in the plenum for auxiliary heat and drop the radiant idea for the basement? What would a fireplace or wood stove do to the equation?

Btw, JONR: Wells by other names: How about production point and injection point?

agagent3: City Covenants...what is the language re: Wells?


I vote for radiant pipes in the basement floor, used or not. 4 inches of foam ( heat flows from hot to cold - big R's in the lid and little in the floor makes no sense for efficiency) And while I am out on the limb, a 3 ton unit.

This house should outlive you and the decisions you make for your own mileage.


Wood Stove heat I know...it is a big commitment of time to get the wood, cut and split, stack, bring into house, burn, cleanup. We burn about 10 cords/year. I have a SS loop in the stove that makes some of my DHW. Voided the stove warranty with that mod, but it works well. One could have a SS tank around over a stove and stay legal. If you are putting in a fireplace, well, maybe a mass fireplace can put out btu's.

ps: not an expert here:}

Posted By agagent3 on 10 Jul 2013 05:25 PM
I'm attempting to learn from the experts here. So is the consensus for this gentleman's solution to go with a 4 ton GSHP. an electric strip in the plenum for auxiliary heat and drop the radiant idea for the basement? What would a fireplace or wood stove do to the equation?

Fireplaces are grossly inefficient while burning, parasitic energy hog air leaks when not burning, and have no place in a high-efficiency home.

Wood stoves put out a lot of heat, but need to be running at half it's max-rating or so to stay in the high-efficiency mode. Even fairly modestly sized wood stoves can deliver over 50,000 BTU/hr, so if you go that route, be realistic about the part of the house that has good convective heat transfer and run the heat load numbers on that portion, and be careful not to oversize the wood stove by more than 50% for the wood stove zone.   In high-R/low-load houses it can be better to go with a high-mass ceramic or soapstone wood stove than cast iron or steel. High thermal mass stoves can be burned using an intermittent but high-fire strategy without turning the place into a sauna. They're pretty crummy for doing quick fires for bringing the temp up quickly, but they'll be still putting out significant heat long after the embers have gone out.  For a house with a 4-ton heat load don't use any woodstove rated over 65,000BTU/hr even with an open floor plan or you'll be forced to run it in it's most-polluting/least-efficient smolder mode. A 45-55KBTU/hr high-mass stove will work out a lot better.  Non-catalytic EPA-rated woodstoves are lower maintenance than catalytic versions, and with most models you can see through the viewing window whether it's hot enough to light off the secondary burners, which is what boosts it from 50-60% steady state efficiency to 75-85% efficiency while lowering the soot emissions down into the single-digit grams/hr range. Keeping the burns in a higher-temp range also keeps the viewing windows from sooting up. 

Ducted combustion-air kits are available for most wood stoves these days, and while not absolutely necessary for normal operation in even fairly tight homes, are a good idea to limit backdrafting potential for those periods when you have the clothes dryer, kitchen exhaust, & bath exhaust all running at the same time.

Putting the PEX in the slab whether you use it immediately or not can be a reasonable thing to do, since the expense is pretty low, and the potential future comfort-factor boost pretty good.  Even without radiant heat in the slab it's reasonable to put 2-3" of EPS (R8-12) under basement slabs in most of the US.  R10 is required even for unheated slabs in US climate zones 4-8 under IRC 2012, with R15 as code-min for radiant slabs.   By some analysis R15-R20 can be rational even for unheated slabs in climate zones 7-8. See Table 2, p10 of this document. 

EPS is preferable to XPS for this application, since the additional thickness has no impact on other aspects of the structure, it has a far more stable long-term R-value, and uses blowing agents with less than 1% of the lifecycle global warming potential of those used for XPS.  Type-II (1.5lb nominal density) EPS is just fine under 4" slabs, but if the local inspectors want to see identical compressive strength of common grades of XPS you can bump it to Type-IX (2lb nominal density) goods.  EPS is usually a bit cheaper per unit-R than XPS too.  Polyisocyanurate (any density) cannot be used under slabs due to it's hygroscopic characteristics- it's bound to take on water and lose effectiveness over time.

Posted By Dana1 on 12 Jul 2013 01:47 PM

Fireplaces are grossly inefficient while burning, parasitic energy hog air leaks when not burning, and have no place in a high-efficiency home.

Very well said. I am opting to go with Dimplex - No flue, no air leaks, no carbon monoxide, no holes in walls, and 100% efficient due to them being all electric. They can put out 5,000 BTU's of heat. You can also run them with NO heat, just the flame, which then gives the ambiance without the heat.