Posted By docjenser on 22 Feb 2011 01:06 AM
You keep ignoring the fact that your heatpumps had extracted
a large amount of out of the ground

Yep. If the EWT & LWT figures (25.6, 21.2) given earlier are to be believed,
and flow is 3 gpm/ton or more (a reasonable guess, given the 3/4 hp pump),
each unit is delivering at least 35k BTUH. That meets or slightly exceeds
WaterFurnace's specs for EWT in the mid-20's.

Early in the heating season, when EWTs were in the 40's, each unit was
probably producing 20%-25% more heat, but the house appears to be
leaking BTUs more quickly than a 5-6 ton loop can support -- so EWTs
have fallen significantly, and will continue to fall (until lockout).

As DOC says, adding more bore can raise late-season EWTs a little,
but it won't have any appreciable effect on your heating bills. A few
degrees increase in EWT has very little effect on your cost per BTU.

...insulate!

Looby

Posted By Princeton N.J. on 07 Feb 2011 07:40 PM
Thank you for all this info. Our heat loss is likely because our 70s-era ranch house is up on piers (a zoning demand when it was built bc of local drainage issues) and also bc like most 70s places, it has lots of windows, glass doors, high ceilings, and three skylights. We had a pro energy audit last year that suggested doing more insulation -- and maybe even insulating the bottom of the house.

Are you suggesting that perhaps with a "tighter" house, our loop could handle the load? It wouldn't help the EWT, would it?

Another thing I've read on this thread is that some people think the problem might be that we only keep our house at 66 degrees (because we don't want to waste energy and also it's just comfortable for us at that temp). Does the interior temp of the home affect the EWT and LWT?

Again, I appreciate your help.

I think your misunderstanding how the geothermal system works. The loop to too cold because the heat pump extracted too much heat out of the ground during the heating season up to this point. It's unlikely your Entering Water Temperature (EWT) was so cold at the beginning of the heating season. As the Geothermal system ran from the beginning of the season to now, it extracted heat out of the ground via the loop.

A "Tighter" house would help the existing loop handle the load, but I would say it have to be badly insulated and drafty for it to be the complete solution. With a better insulated house, it would reduce amount of heat required to heat that house (and less heat extracted from the ground via the loop), there by making the loop last longer before the EWT drops too low for the system to stop working correctly. Also anything you do this year will not be reflected in the EWT, there's pretty much nothing you can do at this point to get your EWT numbers up. Any improvements or fixes you do will help you with next year heating season. 

Yes the Interior temperature directly affects the EWT and LWT.  If you set your thermostat to 68 degrees, the geothermal system will have to run longer and extract more heat out of the ground to heat the house, as opposed to a lower thermostat setting of say 66.

I'm not an expert in these matters, but I would venture a guess that the system loops are too short. Longer loops, weather it was from more drilled loops added or more pipe in a horizontal system setup would give you more ground to extract heat from.  A larger heat sink would allow you to extract more heat from a larger area of ground without affecting the EWT as much.  What ever the issue is, you shouldn't have to keep the house temperature at 66 all winter, the system should be designed to handle a 72 degree house temperature 95% of the winter without Aux heat or the EWT temperature falling too low.


I don't recall weather or not you ran your Air Conditioner (cooling) during the summer.  Running the AC helps reverse the process, where as your putting heat back into the ground from the house, and raising the temperature of the ground. I guess if you never ran the AC and only used the geothermal system to heat, over time the EWT would drop too low to handle the load during the winter. 

  

Posted By Princeton N.J. on 22 Feb 2011 08:02 AM
I see your point. But I have two questions: how do you know we extracted a lot of heat from the loop? I've been told that the loop is cold because it's too short, not because heat has been taken out of it. I'd like to know the other side of the argument.

Second, it's true that our house is not as "tight" as it could or should be. But no matter, wouldn't it be somewhat better if we had a system built upon the right loop-to-tonnage proportions? It may not be perfect, but it could be better.

Thanks for your honest opinion.

The more heat you put in the house, the more you need to take out of the ground. Your loop being at 25F does not mean that it is not performing, You could have the more loop bringing your EWT up to 30 degrees, but you would only save may be $100 a year due to higher efficiency, at the cost of may be $6000 drilling. At the end of the day, you pay for putting a certain amount of heat into your house. I can run the calcs in a few days for you, given you the exact number on the weekend (traveling right now) how much you would save with 30F EWT.
Don't get me wrong, I like large loops, and I would likely install larger ones, but with drilling costs where they are, it is sometimes worth it to shorten the loop a bit to save you significantly money upfront, with only minimal performance impact. That appears to be your case here from the data you have given us.

Noooooooooooooooooooooooooooooooooooooooooo!

Princeton:

Solar is fine and dandy to consider on its own...but it clearly isn't the smart thing to do here.....

I've just read all 13 pages of this thread, and I really gotta say you're coming to the wrong conclusion about your energy use issue. And plenty of far more knowledgeable people than me have been trying to point you to the right one in this thread. Your loop is almost but not quite adequate for the load you are placing on it. Fortunately in your particular situation you have a much simpler and less expensive fix available than adding more loop. 8 tons for 3000 sf of 1970's vintage in New Jersey, with no insulation on the exposed, elevated floor. Talk about yer low hanging fruit here!

You can reduce heat load demand fairly easily by tightening up your building envelope with more insulation, weatherstripping, and caulking to reduce the heating load so your house requires less than 8 tons. Several hundred bucks of insulation in the attic and floor, and some DIY time and effort on weatherstripping and caulking will work wonders in your rather unique particular situation. Granted your loop temps won't instantaneously recover, but you will see improvements in energy usage starting the day the insulation is installed, and your loop temps next winter should be a little better.

The only questions here are how much insulation to install; of what type; what the overall improvement in heat load will be, and whether you can DIY or need to bring in a contractor. If it were my house, and assuming wer're talking about a typical 1970's attic, I'd blow in enough celluose in the attic to reach at least R40+ (adding rafter-soffit vent chutes to ensure proper ventilation of the attic), and debate between rigid foam, spray foam, or batts on the bottom of the house between the floor joists to bring the floor to at least R25. I might even suggest spending a little time playing with some heat-loss calculation software first to see what gets the biggest bang for the buck.

See here for the recommded insulation values for your locale: http://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation_table

Then after you've spent a few hundred on insulation and are seeing the energy savings, you can contemplate spending tens of thousands on a grid-tied Solar PV system.

I totally agree on insulation, but you should get the advise of an expert considering your situation. I believe I suggested before that you should reach out to Dana1 on this forum for information. I still believe you should.

I wouldn't be surprised if properly insulating your house costs more than hundreds, but money well spent if the right insulation is used properly. You may want to begin with an energy audit that includes a blower door test and thermal imaging. I heard several years ago that it is better to get the audit done (maybe it was just the thermal imaging part of the audit) when there is a large difference between indoor and outdoor temperatures. I do not know if this is still the case.

Posted By Princeton N.J. on 23 Feb 2011 10:50 AM

What you say makes a lot of sense, and it's really helpful to know. Thank you. I have a much better understanding of all the possibilities now -- so I really appreciate the explanation. Maybe installing solar panels is a smarter way to control my energy costs.

I second that NOOOOOOO! The best way to control your energy costs is not to waste your energy!

I'm going to invest first in insulation. You're right. Thank you.

Now you are on the right track - adjust the house, not the system.

Yep. I'll look at adjusting the house -- then if there's any $$ left, onto the system. Thanks.

I promised you to run some numbers.

It takes a 180,000 KBTU/H design load to drag down a 1.25" loop with 3 x 255' vertical boreholes in Princeton, New Jersey, to an EWT of 26 degrees F (assuming your grout is average) with (2) 4 ton waterfurnace heatpumps.

That is crazy, it sounds like you are keeping the windows open. Assuming 54 degrees ground temp, and average rock conductivity of 1.4 for ballpark numbers. I show $3200 of heating costs annually, to add another loop of 255' would bring your min loop temp up to 31 F, and run the system more efficient, and save you $340 per year, so it is a bit more than I thought. But again, that is not your problem. Your problem is the 180.000 btu/H heatloss in Princeton,NJ weather with a 2200 sqf.

Don't worry about your geosystem, start really worrying about your house....

Thank you for running the numbers for us. It's really generous and very helpful. I see what you mean and the new plan will be to work first and foremost on the insulation!

Or close those windows....

How well does the system run in the Summer?