I'm finally getting close to pulling the trigger on Geo after about a year of thinking about it. For those interested in my struggles, see these threads:

http://www.greenbuildingtalk.com/Forums/tabid/53/aff/13/aft/80100/afv/topic/Default.aspx
http://www.greenbuildingtalk.com/Forums/tabid/53/aff/13/aft/80332/afv/topic/Default.aspx
http://www.greenbuildingtalk.com/Forums/tabid/53/aff/13/aft/80857/afv/topic/Default.aspx

For those who would like the short story - I have a 2100 sqft ranch in Essex MA. I've lived in it for one year. I'm currently heating with electric baseboards and a wood stove insert I bought used after seeing my first heating bill. I have a full and open basement. I recently upgraded my insulation to R55/60 in my attic and did air sealing with a blower door test showing about 2.5 ACH/50. All windows are casement double pane, and although I haven't, I plan to insulate my foundation walls (I found in the winter they were in the mid 40s and in my mind is my last major source of heat loss). Every contractor I had quote me told me to plan on 4 or 5ton for geo to work right. So I suffered through the winter to see what my actual load was. I've taken out 600KWH per month for my baseline usage. Below is that info:


As you can see, in general you can see what the insulation did for my heat load. You can also see what the wood stove did. Finally, you can see that This winter my load never exceeded 30K. The house temp was generally 60-68, more often than not probably 62-65 which wasn't particularly comfortable. My wife was on maternity for a portion of the heating season and thus heated all day. After she went back to work, we turned the heat down during the day. Based on this info I'm confident my heat load should be 3 tons. Thoughts?
The contractor that I've selected is proposing the following:
Equipment and Services:
1. Supply and install 3 ton Bosch Geothermal 2 stage package unit with EMC motor.
This equipment qualifies for 30% federal tax credit (please see your financial advisor) and Utility rebates.
2. One Desuperheater.
3. One 9.62 stage electric back up heater.
4. Geocomfort 2 pump flow center with hose kit.
5. Complete duct system with registers and grills.
6. One programmable thermostat.
7. Anti-freeze the system.
8. All ductwork to be sealed and insulated.
9. Mechanical permit.
10. Test operate.

The well proposal is as follows:
(1) 510’ Bore hole
Loop Length: 510’
Diameter of pipe: 1 ¼ ”
SCOPE OF WORK
Up to 40’ of 6” pipe casing into bore hole
Drilling of vertical bore hole*
Install vertical ground loop
Grout vertical bore hole*
Install horizontal lines
Pressure test system
Purge and fill system up to the flow center with 20% glycol solution
Trenching and backfilling of horizontal lines
How does this look to everyone?
I realize that in order for the desuperheater to be useful, I will need a buffer tank. Does that tank need to be the same size as the water heater?

You list 510' of borehole, which would make a 1020' loop length. But you list 510' loop length. Please clarify.

Who selected a 2 pump flowcenter. You should only need 1 pump, saving you $80/per year.

What happens when they have to case more than 40'?

Part of determining heat load is design temp delta. If you are going to use consumption to determine load then it needs to be based on actual not a 6 degree swing.

This winter my load never exceeded 30K

On a short term basis? Keep in mind that the system should be sized for some percentage of maximum load, not monthly averages.

I'd make them specify which grout they are going to use - some perform much better than others. Even better would be if they guaranteed a certain COP (efficiency level) for the system - but that won't happen, it's unlikely that they can even measure it.

which grout they are going to use - some perform much better than others

Specifications of the grout mixture must be 0.88 conductivity.

What happens when they have to case more than 40'?

In the event additional casing is needed the cost is $16.00/ft



I guess in my mind, since the average load didn't hit 3-tons, I'm pretty comfortable that sizing the geo as 3-tons should be good. I have the stove and the electric backup if needed, and as I understand it, it is generally best not to over estimate load with geo. Is my thought process on track?

You don't have data for a month post insulation without running the stove. 3 ton looks about right or slightly too big, but maybe one of the number crunching guys could cross check.

-As, doc said, only 1 pump is needed at this size. This saves real $ on pumping.
-Do they offer a non pressurized flow center for the loop? This is not needed but is nice if you ever need to open up or purge the loop.
-Maybe use single vari-speed pump on flow center and control by stage to further save on pumping.
-Use Methanol as anti-freeze, if allowed locally. Improves flow, heat transfer/effieciency.
-Use thermally conductiive (TC) grout on bore. Its just special sand added to the mix.
-Insulate all the interior loop piping/flow center to prevent condensation.
-Connect desuperheater to buffer and insulate those lines. Make sure you get the buffer or don't bother. 40 gal or larger size should be plenty.
-Make sure you understand the programming on the thermostat and how it controls the staging of the Aux heat use. Simple set-backs and temp bumps can trigger Aux use needlessly and ruin your efficiency. This issue exists on many fancy thermostats.

Looks like a nice project. Glad to see you hit the load first.
I'm sure someone will mention splits at any moment.

since the average load didn't hit 3-tons, I'm pretty comfortable that sizing the geo as 3-tons should be good

You might be right, but just to illustrate the point, imagine some place in the desert where the monthly average is 70F (0 tons needed!) and yet some night's temperatures go down to 35F.

......sizing with 3 ton should be good......
While you've done some math you simultaneously pollute the data by not maintaining temps agreeable to your wife.

How much does such a system cost (parts and labor)?

My quotes are all around $35,000 - yes painful I know...

You might get a price on a Daikin ducted (not mini split) air source heat pump before you spend that much. Also a horizontal loop.

Ducted ASHP came in at about 20,000 - after rebate only $5,000 difference with Geo, however the ASHP requires me to maintain a backup heat source also

That seems very high for a ASHP. What was the SEER? I assume you are only going to have the ducts for the first floor and not basement?

see this thread for info on the ASHP - http://www.greenbuildingtalk.com/Forums/tabid/53/aff/13/aft/80332/afv/topic/Default.aspx. It was a Bryant. Problem for me is no matter the direction I choose, I need duct work. My house isn't quite open enough for mini-splits, thus the conclusion to pursue Geo

So you've already had estimates, what did they conclude your heat loss was?
All properly designed heat pumps (ground or air source) of yesteryear have auxiliary heat. With new variables that may not continue to be true, but cost v benefit may still dictate aux.

shockingly, only one of four has done a manually J which came out to 41,000 before insulation and sealing improvements. Detailed measurements where not taken so I would describe it more as an estimated heat loss. Everyone claims they will do a real manual J after I hire them. There is also a lot of talk that closed loops don't really produce their full potential. Something about 10% loss so in reality a 4-ton is actually a 3.5 ton

It was a Bryant.

That's not a Daikin.

You could shoot for doing this with a single ductless minisplit. $8,000 - $10,000.

With baseboard everywhere and wood backup, you already have the aux needs covered.

Have you posted a floorplan of your house? Need to have the rooms labeled as to use.

I'm thinking you need to look for a geo pro.

Given the extensive envelope improvements and the apparent propensity of the locals to oversize, I strongly recommend having an independent load calc done. Let me come right out and say what guess Joe is hinting at - a 2 ton system may actually be a better fit. It'll work better in summer. I grew up in the next town over and it seems to me summers now have many more hot humid days than they did 30 years ago. I know that is not scientific and that my southern climate bends my thinking about humidity.

Regardless of summer considerations, all systems SEER / EER / COP ratings are at lab conditions, and part of that is steady state operation. Right sized / slightly undersized systems run longer, potentially getting closer to lab ratings.

Given how much analysis you have already done, why not do it yourself? For $50 you can download a 60 day license to use HVAC calc

Again, please clarify you loop length. You are also mixing up average load and peak load, your 3 ton guess might be right, but uncertain right now.