I'll give you a building scientists' perspective - bonus rooms are often thermal nightmares. Since they're seen as bonus rooms, they're often built with little consideration to the thermal and air boundary, resulting in vastly greater heating/cooling requirements than an equivalent square footage of main house. Exactly the type of thing you described. That single uninsulated, leaky door could easily be doubling the heating requirements of that room. What you describe for the stat could very well be making the system "think" that it can't satisfy the home's heating requirements sufficiently using pure GSHP heat and forcing the electric heat strips on far more than they should be. Builders in general have no clue about the negative ramifications of such construction practices. Likely too, the joist bays that run from attic space under the bonus room are connected, allowing cold air to circulate under the floor, another horrible practice that turns bonus rooms into refrigerators. You sound like an intelligent consumer, willing to delve into the nitty-gritty of your home. As somebody said early on, you'd be best off to combine this analysis with a comprehensive home energy audit so that you can really get the most from your system. Finally, given everything you've described, I'd just leave the electric resistance strips forced off as long as your home is comfortable and the system can keep up. Then you never have to worry about "thermostat wars" forcing the system to backup and you know you're always running at GSHP efficiency. good luck!

tinoue,
Thanks for the perspective. I think you are right on the money with your perspective regarding the bonus room. The ceiling area is very well insulated with roll insulation up to code however the hollow interior door leading into the attic completely compromises the area from a thermal and air boundary perspective. I am not going to turn on this area until the contractors who installed the thermostat moves it to a more appropriate wall, and I will seal the door jam and apply some insultion foam on the backside of the door and fit some sought of seal on the bottom of the door given that it is a regular interior door with no sweep. Thanks you

Location of the thermostat in an appropriately insulated thermostat is of little importance (barring exposure to direct sunlight). The goal is not to move a thermostat to a warmer part of a room but to insulate the room so that there aren't cold spots.
J

Thanks joe.ami,
My concern is that will I be able to insulate that hollow door sufficiently to prevent the thermostat being negatively impacted. I am not trying to move it to a warmer part of the room thereby causing the reverse problem, but merely out of an area which I may have problems insulating effectively. The stat is literally 12 inches from the door jam. The wall it is on does have insulation on the backside of the drywall. That attic area has some serious temp issues in the middle of summer and winter as you may well know. Thanks for your ongoing feedback and insight.

Now that I have stopped the bleeding a little I would like to ask how much should the geothermal cost to run in the middle of winter given that it is a 4000sf home with a 5 ton unit. At the moment the only cost comparison I can make is with my old home in Northern MD which was 5000sf and peaked with a utility bill of $540 in the middle of winter. Should I expect to see a cost saving based on the fact I was using 2 gas furnaces for that home? Any thoughts??

$257.83

Just kidding. There are just too many variables to say for sure (like insulation, air infiltration, outdoor temperature, thermostat settings, etc.) You can watch your electric meter to get a feel for what your monthly usage may be. You could also ask your installer if he can still run numbers for you based on the older equipment that you have, but I wouldn't tie them up too much and risk upsetting them if they can't do this easily. Maybe they have copies of the original paperwork that was done...

Is expecting a cheaper geo bill for this new home achievable given that geo is always sold as a cheaper option than gas furnaces and and ac unit? Over the summer I saved about $150 compared to my bill in MD. Obviously at the moment I am seeing zero savings. While I realize that there are many variables that go into calculating the heating cost one has to keep in mind that this home was custom built by a reputable company for the mother and sister, so no cost was spared with regard to materials used. During the home inspection all insulation etc etc passed according to spec.

There are a ton of variables and unknowns however I've had great luck doing operational cost comparisons if you know what you're comparing. For example, you mentioned that you're paying ~$0.10/kwh. You can reasonably compare this with, for example, a 95% natural gas furnace with NG at $x.xx/100CCF, and an 84% oil unit with oil costing $y.yy/gallon. The assumption you make is that you're pumping all of them through the same ductwork in the same house, so those factors roughly drop out of the equation. You then put in your best guestimate for the geothermal COP based on the EWT and the manufacturers' spec. With a little spreadsheet work, you can get a nice comparison of relative operational costs.

What I've done to get a very accurate read of a home's heat load is to use a multi-channel data logger. One channel measures a representative indoor temperature, another measures return air temperature, a third measures supply air temp and a fourth measures outdoor. A few days running on pure electric resistance heat, since you know the kw of the heat strips, will tell you quite accurately how many BTUs are being delivered into the ductwork at what outdoor temperatures. This gives you a quantitative measurement of what your home's actual heat loads actually are at a variety of temperatures. It's not perfect, but it's way better than any other measure I've used.

If you're willing to do this type of experiment, you will learn a huge amount about your home that can be used to assess exactly how your GSHP is performing and how your home compares to others of similar size. This fall, I did a couple of jobs for HVAC guys near me (Philly area) where we did this and it resolved issues that they'd been battling with for months. There isn't any substitute for hard data.

Stan,

You've turned off the resistance heating - now you're operating on geo and without the bonus room the system appears to be keeping up with appropriate (manageable) energy usage. But at the end of the day your problem is an undersized system which will never heat the entire structure properly. For a/c it's ok, but you're likely upwards of 30,000 BTU's undersized. There's nothing you can do other than supplementing heating with a less costly (than resistance) alternative - like a ductless split in the bonus room after first tightening the thermal envelope.

Paul
www.TotalGreenUS.com

Yesterday at 2pm I turned the Diningroom stat up by 1 degree to 66 F. In the last 24 hours the usage jumped from 131 KWH to 154 KWH with only a 1 degree increase in temp, is this normal to see such a large increase?

Paul,
Thanks for the feedback. I think you are the first one to mention about the system being undersized. I cannot come to terms with the fact that a 5 year old home is so difficult to heat. Everyone in my neighborhood has gas heating and none of them have a utility bill anywhere near what I am paying for a similar sized house. While I realize that every house has different influencing factors and every house is different in shape, it would appear that keeping my heating at the current settings and not even having the bonus room on I will be getting a utiltiy bill for about 4620 KWH. To me that is unacceptable given that geo is sold with cost saving over gas. Am I being unrealistic in expecting a more efficient system.

While I realize that I can get an energy audit, install different monitoring devices etc in an effort to reduce my costs, I feel that given the fact that the home is relatively new and modern construction with a geo system I should not be having this kind of inefficiency. At what point should the installation company admit that the system does not perform sufficiently and come up with some real solutions. Given the data I have from the utility company for the last 5 years over the high usage winter months this system has always been inefficient. Any ideas.

Good question. Everything else being equal, I have noticed (no data) that for every degree increase in heating mode (or degree decrease in cooling mode) there may be a non-linear (correct word?) increase in the run time of the unit until the system runs 100% of the time at which point there can be no further increase in run time. At that point, if the thermostat can't keep up, aux heat may engage if enabled in heating mode.

If this is correct, and it may not be, the electric usage for the next incremental degree (66f to 67f) will result in even more electric usage (due to a longer run time) than the 23kWh increase from 65f to 66f.  Is this correct?

geome,
I still have the Aux Heat turned off. I noticed this morning with very similar conditions outside that the geo ran 100 minutes to satisfy the stat compared to the previous morning where it satisfied the stat in 60 minutes. My frustration is that this system should be running more efficiently or am I crazy. Most people I speak to in my neighbourhood have their temps set at between 68 and70F at the moment and their utility bill is less than mine. My question is where is my savings compared to gas. I have spoken to several people who have geo systems that are efficient so you can understand my ongoing frustration.

Is there much difference in the various solutions used in the loop. Someone told my wife at work that he had the polyetylene glycol mixture removed from his loop and used a mixture with Methanol and noticed dramatic improvements. Is this a possibility?

Stan,
Now you see the problem with home building. Once the drywall is up and the granite counter tops are installed the homeowner has very little recourse if the insulation and air sealing were done incorrectly. Insulation is an easy place to cut corners because it is hidden. No increase in efficiency of a geothermal system makes up for a bad envelope. The fact that it is new doesn’t mean squat. Lots of big houses are built poorly. Most people base their buying decisions on square feet and shiny counters, not the bones of the structure. They find out about that stuff down the road.
One way to look at your problem might be to disable the geo part and run aux heating only for a day and measure the kwh used, then run geo only with aux disabled and measure kwh used on a similarly cold day. This will give you a crude estimate of the cop of the geo.
Half assed math follows:
If you are consuming 4600 kwh/month to heat the house, even if you used resistance heat, that would be 15 Million BTU’s per month. If that was with the geo system and you had a cop of 3, that would be 45 million btu’s/ month.
I looked it up and there was aprox 1000 hdd for December
So to get a usable metric for energy, put your energy consumption of the house into btu/sf/hdd
A COP of 1 = resistance heat 15 Million btu’s used
15,000,000 /4000 sf/1000 hdd = 3.75 btu/sf/hdd
COP of 3 Geo thermal 45 Million btu’s needed
45,000,000 /4000 sf/1000 hdd = 11.25 btu/sf/hdd
These are back of the envelope ballpark figures, Use
http://www.homeenergy.org/consumerinfo/benchmarking-energy-usage.php
To compare yourself to others. Remember the average age of a house is around 40 years in the study. And the study was 14 years ago
Code min insulation done with some care should get you under 5, A really well insulated house can get you under 1.
If your geo system is working properly, your insulation sucks. If your house was semi well insulated, it should use that much electricity if you used resistance heat only.
I think the best thing you can do to save money is get a good audit, blower door test, thermal imaging and duct testing and figure out what the problem is.

Good Luck.

Eric

Posted By stantheman on 13 Jan 2011 09:48 AM
geome,
I still have the Aux Heat turned off. I noticed this morning with very similar conditions outside that the geo ran 100 minutes to satisfy the stat compared to the previous morning where it satisfied the stat in 60 minutes. My frustration is that this system should be running more efficiently or am I crazy. Most people I speak to in my neighbourhood have their temps set at between 68 and70F at the moment and their utility bill is less than mine. My question is where is my savings compared to gas. I have spoken to several people who have geo systems that are efficient so you can understand my ongoing frustration.

Is there much difference in the various solutions used in the loop. Someone told my wife at work that he had the polyetylene glycol mixture removed from his loop and used a mixture with Methanol and noticed dramatic improvements. Is this a possibility?

Someone else will need to answer the loop question (I have nothing to compare my loop solution to.)

Your system ran 40 minutes more but the temperature in 1 zone is 1 degree warmer and although seemingly similar, we don't know the impact of the outdoor temperature, wind, sunlight (assuming the 40 minutes was after dawn and would effect this zone directly or indirectly.)

A comprehensive energy audit may fill in the unknowns.  I plan to have one done this year.  Getting the manual J from the installer, if he has the old one would be a starting point to see how he sized the system.  I have read on forums that zones done properly can be fine, but they need someone experienced to do them properly.

What jumps out at me is that you've noted a hotter than normal Summer yet your Summer cooling hasn't been a problem. That might help the mechanical engineers localize a heating plant issue, but because I don't know anything about that, I am thinking about a different angle.

I'm more suspicious of your building envelope and I'm taking a bit of a clue from the uninsulated and unsealed door you described. Regardless of the assurances you've heard about how the build on your place went, I would say it is always possible that someone skipped a step. That door is my first clue and my second is the Summer/Winter disparities you have described.

Assuming you've investigated the windows and they are what they seem to be and that you've searched for any noticeable air leaks or ducting issues, the next thing I'd look at is your slab foundation.

What is the r-value on an uninsulated slab? R1?
What is the difference in heat loss between that and a "normal" R10? Plug those numbers into what you are seeing and something might pop out.

I'd consider coring that slab to look for the insulation.

And, if you do find insulation, I'd then investigate whether the slab was adequately isolated from the exterior foundation.

Seems to me that there are plenty of 4,000 sf homes that can be handled with the capabilities of your system.

It looks like Eric has been barking up this tree for a while now.

There's no substitute for an energy audit. A blower door and an infrared camera will show you in a couple hours what no amount of guessing or twiddling with your system will give. You've got too many variables, even in these simple tests. This will also quickly detect bad ductwork, something that needs to be eliminated as a variable.

ICFHybrid,
I spoke to the township building inspector who oversaw this project and he informed me that the slab was installed with all the appropriate measures and with 24 inches of foam around the exterior foundation. He is very familiar with the home given that it is the only one on a slab in the neigborhood.

What is the soil type you are on and what is the depth of the water table? slab on grade with no underslab insulation is probably a big part of your problem.

Also one that is inherently very hard to deal with.

eric

"all the appropriate measures"? That's what he said? It's the only other one on a slab in the neighborhood?

Okay, now I would core it for sure.

Do you have a set of construction plans for the home? I'd core the slab first and then, assuming you find insulation, I'd core the foundation in such as way as to find what is supposed to be isolating the floor slab from the exterior wall foundations.

This is assuming that you have visually verified all the other insulation and have done at least a cursory check for large gouts of warm air from the ducting or other major cold air leaks in the house. And, I assume by now you have plugged up the bonus room door issue.