I have a new construction 4500 square foot house that is 2.5 stories with 6" of sprayed foam in the walls and ceiling. We have two 4 ton geothermal units that handle the conditioning of the house very well. Our first power bill came in at $450 with consumption of 2900KW which surprised me a little bit. This month we are closer to 2700kw. We have not been too terribly hot, the units run on high about 2 hours a day and on low about 12 hours per day.

So I think the part that is surprising me is that the thermostat shows energy consumption information which hasn't matched actuals. In looking further, I have one unit running on low right now which is using 3120 watts and the thermostat claims it should be using 2050.

I do know part of the difference is that the pumps (4 250 watt pumps) are all parallel and all run when either unit kicks on. I'd like to look into this and maybe change it, but the installer is resistant to the idea. I don't know why.

Design day heat loss was 72k BTU cooling and 90k BTU heating. The equipment is waterfurrnace 5 series 2 stage units, 4 tons each.

The thermostat power readings do not include pump power. Where are you getting your power reading? The difference could be the pumps. Your pumping system is very inefficient, pumping for 8 tons when only 2.73 tons is running. For the price of 4 conventional pumps you could have had a variable speed pump that adapts to demand. Also, you are oversized as to installed capacity which also contributes to inefficiency.

The thermostats usually display the fan power, the compressor and the circulation pumps all separate. Having 4 circulators to pump 24 gpm is crazy enough, 2 should do the job, but having them come on all at once is even more wasteful. You should reduce your pumping power in order to have your system run efficient. Can you tell us more about he design of your loop field. Length of pipe, number of circuits, diameter of the pipe.

Posted By Estrogen Hostage on 01 Sep 2014 11:50 AM
I have a new construction 4500 square foot house that is 2.5 stories with 6" of sprayed foam in the walls and ceiling...

What kind of spray foam?  Open cell or closed cell? 

Judging by the size of equipment and the load, I would say your designer is "un evolved". Besides oversizing equipment for the load, a 90 MBH load for a tight house seems like that was padded as well exaggerating the faux pas.

Where are you located? Something is off. Your Heat Pumps (8 tons) engaging into 2nd stage in "not so hot weather" is unusual for a foam insulated 4500 sqf house. Huge glass fronts? Southern exposure?

OK - I have lots of things to answer: 1) I have a horizontal 6 pipe loop, 3/4" PE pipe. Soil type is silt/clay - damp. One pipe at 7', the other at 5' - 1105' of total trench. Coming off my loop pump to the manifold is 1.25" pipe. 2) Location is near KCMO. Temps have been very reasonable this year, and my loop is starting at optimal temperatures. 3) I do have a LOT of glass in this house, all Marvin Ultimate windows with low U factor. No huge southern exposures though. 4) It wasn't going into high as much until I added setbacks on the thermostat programming. I figured it was easily catching up and with the circulating pumps running so much I decided it was cheaper to run in stage two than in stage 1. I am not convinced this is saving me any money. I may change it back. 5) Insulation is 5.5" of open cell insulation. 6) Total KWh in a month is right at 3000 two months in a row now. That's a $450 bill.

The thermostats do have a setting in there for the pumps. They show 492 watts each when they are running. This is somewhat inaccurate because all four are on if either unit 1 or 2 is running. It still doesn't account for the discrepancy in power consumption alone. I have spoken to the installer. He does about a thousand systems a year. He said he thinks this is normal.

How are you measuring 3120 watts and what does it include?

Clamp on ammeter in the breaker box. I got 13 amps while the unit was running in stage 1 cooling with four circulating pumps running.

Posted By Estrogen Hostage on 02 Sep 2014 06:30 PM
The thermostats do have a setting in there for the pumps. They show 492 watts each when they are running. This is somewhat inaccurate because all four are on if either unit 1 or 2 is running. It still doesn't account for the discrepancy in power consumption alone. I have spoken to the installer. He does about a thousand systems a year. He said he thinks this is normal.

????

We routinely attain 1200 - 1500 SF / ton in new construction, so your 4500 SF house may have approximately one 4 ton heat pump too many. Rampant oversizing causes extremely low efficiency operation.

Mis-designed pumps are often the energy Achilles heel of a geo system.

Ammeters don't account for power factor, which means the result is often too high when calculating watts for motors.

Posted By Estrogen Hostage on 02 Sep 2014 06:30 PM
The thermostats do have a setting in there for the pumps. They show 492 watts each when they are running. This is somewhat inaccurate because all four are on if either unit 1 or 2 is running. It still doesn't account for the discrepancy in power consumption alone. I have spoken to the installer. He does about a thousand systems a year. He said he thinks this is normal.

I assume the pumps are 26-99 Grundfos. I don't know an installer doing 1000 installs per year, even if he has done 1000 in his lifetime, if he thinks it is normal, he has not learned yet on how to make a system efficient. Each heatpump should have 1 circulation pump each going for itself, and that circulation pump should not be running unless the associated heatpump is running.More sophisticated systems would have a single variable speed pump serving both heat pumps.

In addition, (2) 4-ton HPs need nominally 24 gpm, 6 parallel circuits cause a very high pressure drop (flow resistance), in addition your 1.25" header pipe is too small for 24 GPM, no wonder you need so many pumps to push enough water through for 8 tons. What is your Entering water Temp? And let me ask you how you make your hot water?

Posted By engineer on 02 Sep 2014 10:29 PM
We routinely attain 1200 - 1500 SF / ton in new construction, so your 4500 SF house may have approximately one 4 ton heat pump too many. Rampant oversizing causes extremely low efficiency operation.

Mis-designed pumps are often the energy Achilles heel of a geo system.

Regarding sizing, I had three bids on this and all were in the same ballpark on sizing. I am assuming it not to be too far off. I know that the heat load was driving the unit requirements, and that's why I wanted two stage equipment. It was also my requirement that there be two systems on account of the fact that the house is very tall and I didn't want complicated zoning. Company A quoted Tranquility 27 systems of 3 tons each with vertical wells. Company B quoted one three ton Waterfurnace system of 4 tons and one of three tons, and C got the job with two four ton waterfurnace systems. I could be wrong about the number of systems he does per year. I will say that I know it is a LOT. That's why he got the job, company A has only done three or four ground source heat pumps, and company C was more local than B. I wanted somebody local that did a lot of systems to make sure the details were right. I do have a copy of the geolink report. I'll find a way to redact it and post it.

I have not been monitoring EWT. Will I get a good reading through the plastic pipe? Hot water is made through a desuperheater. Each unit has a preheat tank, which are parallel to each other and in series with my backup propane water heaters.

I have the relevant pages of the geolink report attached.

Even if only $50/mo can be saved on pumping costs, that will quickly pay for a variable speed pump (perhaps with delta-T control to account for all the different btu combinations).

So the estimate (for sales purposes :-)) was for 4861 kwh for the entire cooling season and you are running at 5600 kwh for two months?

3000kwh/month includes everything in the house. That said, we are pretty conservative with lighting on account of all the windows and our old house had all the same appliances in it and our consumption is easily doubled.

I think it is time to step back a bit and figure out what the best way to proceed is.

You have a large new house that has unexpectedly high Utility bills and you don’t know if it is due to the geothermal system, or to the building itself. First question is whether the building and hvac system was properly commissioned?
Do you know infiltration rates (blower door results) duct leakage rates? Do you have duct work in un conditioned space? What are your expected plug loads based on appliances and other stuff?
If you don’t know this info, now is the time to bring in a professional to audit the house, either a HERS Rater or similar to evaluate the shell of the house and also figure out what the electrical usage in the house is, not attributable to the heating/cooling system.
You will want shell leakage, duct leakage, and overall heat loss. While you are at it measure airflow and delta T at each register, as well as airflow and delta T across the coils.
With that info, you can determine whether to focus your efforts on the HVAC system, or other things, or both.

You only have 2 possibilities, first your house is very energy inefficient based on the existing heat loss predictions,(120,000 btus heat loss), or second the heat loss calcs are out of wack in which case your system is incorrectly sized.
I will leave it to the geo guys to help you with system design parameters, but you may need to do a bit of homework on the house itself

First off the design temp is 6 deg F for winter and, with 99 for summer When I look a the charts for MO, I don’t see any region with a summer design temp over 94° so that is suspicious.
They are accounting for 20,000 btu’s of internal gain- that is a lot
The Heating temp diff is 77° which does not match the heating set point -winter design temp

Lots of questions to answer.
Good Luck
Eric