This should be simple to understand...  1kWh of electric power to the resistance coils will supply ~3413 BTUs of heat to your house (this is at 100% efficiency).  Use that same 1kWh to power a GSHP with a COP of 4.0 and you get ~13,652 BTus into your house.  This IS why geo is what it is.

I will make the blanket statement --- stage 3 is always BAD!  It is simply electric resistance, and for most people it IS the MOST expensive way to heat a house. 

In a properly sized system, the 3rd stage (called "emergency heat") is only supposed to come on when the heat pump can't keep up with demand with stage 2 running 100% of the time. 

Setbacks create somewhat artificial situations.  For example, the house drops to 65 at night.  At 7AM the thermostat says it is suddenly supposed to be 70.  The pump kicks on (1st and 2nd stages) but still the house isn't yet at 70.  Stage 3 kicks on because this is "an emergency".  Efficiency of the system drops drastically.

If you want to use setbacks, rather than leaving it at the same set point all the time, do something to stop that electric coil from heating up.  the house will take longer to heat up, but it will be done with the full - efficiency - of the heat pump. 

Regards,
Ed
Mr. Green Dreams

See my house at: www.GouinGreen.com      

 

Sensible setbacks and smart thermostats really should eliminate aux heat except in emergencies, which if I had an emergency, I'd take aux heat!

As of right now, aux is manually off at my house, and I'm trying to see just how GREAT this system is. So far, EXCELLENT! Even with 8 degree setbacks at night and during the day, the house warms right up within an hour or two (it comes on around 4:30 AM to get the house to temperature by 6:30 AM), with no aux heat.

That, in my mind, as a general consumer/homeowner, is what I hoped to see, and I am HIGHLY recommending these systems to everyone I know.

What I'd really like to find out is when EXACTLY the system is coming on early to heat up the house. I was thinking of putting ribbons on one of the floor vents, pointing the laptop camera at the vent, and taking pictures every couple minutes. Then I can look back and see when the system activated for its recovery period! I'll try to find out and post those results, too.

Wow, exciting stuff this discussion.

ok, so going on what you stated regarding lowering efficiencies... I have Climate Master Tranquility 27 units.  I am using ground water (standing column well) so I will never get down below 32F without having freezing issues.  That would call for emergency heat and/or emergency bleed from the well.  In any case, the efficiency table for my units shows:

When running on 2nd stage - at 9.0 gallons per minute with 1250 CFM airflow:  COP @ 50F EWT is: 4.68 / COP @ 20F EWT is: 3.51.

One could argue that even if the COP dropped to 2.0 it is still more efficient than electric resistance (which can never be more than 1 and is more likely 0.95-0.98).

One more general statement - From a physics point of view, temperature change is energy intensive.  In all likelihood, a well sealed, well insulated house is going to use less energy to keep at a steady state (temperature) than allowing it to cool and then heat it back up. 

Personally, I have disabled the setback feature on my thermostats.  Our heating (and cooling) is set to 69F year round.  However, my house is quite a bit more insulated than most houses.

Ed
www.GouinGreen.com   

Wait, what? I don't agree with this at all, assuming that the loop field is properly sized to the 5-ton unit. There's no reason a 5-ton unit can't have the same COP as the 3-ton for a given loop temperature. I could see only 2 places where the system efficiency would be lower for the larger unit - a larger loop pump might be required (partially offset by the fact that the 5-ton will run for a shorter time) and more frequent cycling (not sure how to quantify this). I bet in most cases the aux heat and the slight drop in efficiency for the larger unit would be a wash at worst. Again, it comes down to individual system design and optimization.

If you want to say that the 5-ton will never pay for itself because the additional savings is small I can see that, but I'll need some convincing that the operating cost would be higher.

I agree, when the house is 5 degrees colder than the setpoint isn't an emergency in my opinion, an emergency is when the geo system isn't working period.  Thermostats should be designed to allow you to set emergency conditions, when it's a greater range from the thermostat setpoint you select, or if the temperature drops below X, that you define (maybe 50 degrees).  I too have my AUX heat disabled, but It's disabled via dip switches since the blower and Aux heater are on the same circuit.  There is always the risk that the system will stop functioning on the coldest of winter days when I'm out of town and the house pipes will freeze cause the AUX is disabled.  This is very remote possiblity, but could happen. 

They do make thermostats that "learn" how long it takes to heat a house back up from a setback and automatically adjusts the time it begins heating the house back up based on how long it took to heat the house up from the pervious day.  Now weather or not these are compatiable with geo systems, I'm not so sure.

:)
It's not the first it's been discussed.
Remember this,
I invite my customers to experiment but caution against certain things.
One of which is the assumption that all aux. use is bad. It is after all designed in and among other things saved the H/O thousands on initial investment.
On an estimate the other day the homeowner and I discussed the difference between a 3 and a 4 ton for his job. The 4 ton actually ran for about $70 less/yr but cost $2,000 more to install. With tax credits payback was only 20 years. You can make a case for either, but once it is made if the 3 ton is chosen you might not want to disable the aux. too much.
Have a frank discussion with your installer, and you might spark some interest in him......
"look I was going to get a monitoring system and try different set-backs and such and compare the results, i'd be glad to share the outcome if you're interested." an affirmitive response would be enough to keep warranties intact. If you can communicate via E-mail you'll have a response to print.
Regarding the results you are experiencing right now remember that this weather is mild and it is true you would not need aux. except for situations you are creating. Just remember when it gets cold, you can actually extract btu's from the field that you'd wish you had later. Colder EWT's caused by aux interuption drop COP for the long haul. In the case I mentioned above if he had were to disable aux in weather like last January's he might have spent half of Feb. on emergency heat.
In our area electric rates are such that these "huge" costs of auxilliary heat are measured in nickels and dimes. So if someone's experiment went too far and they had to run emergency heat full out for a whole day, it would cost $18 for a 10K. Even at $540 for 30 days that is still less than a lot of propane bills around here.
So again experiment, but not with the "aux is bad" bias, it is simply one of the possible ingredients to the best performance of your system.
As far as results, run your tests during a winter with temps lower than those on the bin report and you'll have a good measurement of performance.
J

Wow more responses while i was typing.
Ed, we've had this debate before and failed to convince one another, but again what I feel you are missing is that the lower EWT's impact far outlives the aux. requirement. So you are penalizing your efficiency for hours to come to save a few cents now. You also are skipping the point that you must pump more water (now and later) because of this, and if I recall your system is installed at 100% load which may not be true of the folks you are advising.
Respectfully, I only object vehemently to the "blanket statement". We can argue the rest til the cows come home without me getting particularly excited.

CNY,
Look at it like this when first stage is required on the 3 ton mentioned which is a large portion of the year, it is drawing very little amperage, while the 5 ton may still be at or near 20. If you have operating cost calc software plug this in.
The 5 ton costs you more to run (in heating dominated climate) in bumper seasons and all summer it also has shorter run times and fails to contribute as much to the hot water production.
Not loading for 100% is because we know it is for a small fraction of the year. A 5 ton compressor will draw more amps year round than anything but the aux. coil. So yes, you will find the 3 ton cheaper to operate when satisfying all your heating/cooling/hotwater requirements.
j

J - Do you have Geo installed in your home?  If so, please tell us about it.

Utility Bills for my house - Total electric (entire house + geo) and propane (some HW and fireplace for ambiance) - total cost 12/2008 to Mid 11/2009 - $4,843.57

Neighbor’s house – total electric, oil, and cord wood cost since 12/2008 to Mid 11/2009 - $6,124.86

Houses are of similar size (~3,800 fqft) with similar finish materials.  Theirs is conventional 2x6 with fiberglass, mine is SIP.  I acted as the GC.  They hired someone.  My house cost $200k less to build (including land).

I met and interviewed a lot of contractors / sub-contractors over the past 3-4 years.  I have yet to meet even one who cares as much about my utility bills as I do.     

At this time I have no way to separate geo costs from the remainder of the house.  I am working on a plan to sub-meter so we can get some hard numbers.  BTW - Electricity in my area is ~$0.18 per kWh (ouch!).  On average our area has 6990 HDD annually. We do not use setbacks of any kind.  Aux heat is locked in the off position.  The units have never shut down due to low temperature. 

Ed
www.GouinGreen.com

The proponents of 100% geo sizing are missing another significant issue - cycling losses. A unit does not produce anywhere near advertised COPs during the first several minutes of operation. It takes awhile for refrigerant pressures to build.

For example, a 3 ton unit might run continuously to meet a certain load. Alternatively, a six ton unit could meet the same load by running half the time, in theory. In fact, the six ton would run more like 60-65% of the time to compensate for cycling losses.

Morever, within a given manufacturers product line, the smaller units, 2-3 tons, tend to be the most efficient. The bold print claims of "up to 30 EER or 5 COP" tend only to apply to the smaller units. The 5-6 ton units are somewhat less efficient.

PS: When I use major east-west roadways of the Interstate system to delineate different design zones / criteria I am certainly guilty of making "blanket" statements - its just a handy easily-visualized demarcation between different ways to think about system performance

No Ed, I do not have geo in my home, just several other folks homes- for reasons explained here (on this forum) and elsewhere.
Your response neatly ignores all my previous points (and olive branch).
Are you suggesting you are more of a geo expert because of your case study of 1 home than I with my 12 years in geo?
joe

Okay, bill just arrived for December's usage: $200. $100 (as previously explained) is what I'm considering normal usage sans heating of any kind (house/water). So, geothermal cost for December was $100. I'll do all the math in another post about heating degree days, etc. However, the house previously used $300/mo oil for heating, so geo saved $200 last month over the cost of oil (and oil certainly didn't go down much since November!)

My house cost me $2,925 in utility bills (all electric 18,170 KWh) for the year (Nov. 08 to Oct 09), I'm currently running $95 less this year than last. My house is about 3,500 sq ft, located in Southern New Jersey, heated with Zone 1 Geothermal and Zone 2 ASHP.

Month	Bill	Meter Reading before	Meter Reading After	Power used	Average Temp This month	Average Temp Last Year	KWH Daily Averages This Month	KWH Daily Averages Last Year
Nov-08	$222.37	6287	7824	1537	51	47	38.3	54.9
Dec-08	$340.61	7824	10189	2365	41	42	73.9	60
Jan-09	$403.78	10189	12999	2810	37	40	90.6	85
Feb-09	$362.06	12999	15512	2513	33	36	78.5	88.7
Mar-09	$360.27	15512	18016	2504	39	40	86.3	75
Apr-09	$244.69	18016	19704	1688	47	48	56.3	61.2
May-09	$138.23	19704	20640	936	61	58	30.2	43.7
Jun-09	$124.80	20640	21365	725	66	68	24.2	45.3
Jul-09	$173.57	21365	22272	907	72	76	30.2	65.7
Aug-09	$214.55	22272	23385	1113	76	78	35.9	5.5
Sep-09	$206.61	23385	24457	1072	73	73	35.7	29.3
Oct-09	$133.02	24457	25224	767	63	61	23.8	25.6
Nov-09	$192.30	25244	26452	1228	53	51	39.6	54.9
Dec-09	$274.74	26452	28223	1771	46	41	59	73.9

If you interested to know why i bother to track the meter reading, it's because sometime before i started tracking the meter readings the electric company replaced the meter, it was a digital meter and now it's an analog one. I don't know why or exactly when it was replaced, I just know it's not the same meter as the one before.

Here are the updated numbers:
Heating degree days covered by the electric bill: 985
Gallons of oil needed (if I still had oil) : 166
Current cost of oil x gallons needed/used = 2.80 x 166 = $465 worth of oil to heat the home last month
Electric bill was $200 last month, minus $105 (base cost of house usage with no heating/cooling) = $95 to heat using geothermal
Comparison vs. oil = $370 saved vs oil heat.

November 09 savings : $150
December 09 savings : $370

Having never had anything other than Geo in this house, I have nothing to compare my numbers against.  I guess I could compare my figures to a similar sized house in the area that uses Gas or oil, but that's not an exact science. I do have my figures from the year before, and I'm trying to take steps to decrease my energy usage each Month / Year, my goal is to get the energy bills low enough so the electric company is paying me.

Woo Hoo, My 500th post, an Advanced member now. I must know what I'm talking about now.

NOTE: during January I had some thermostat wiring issues, and for about a week, I ran the house entirely on emergency heat.
Here are the updated numbers for January:
Heating degree days covered by the electric bill: 1044 (according to degreedays.net)
Gallons of oil needed (if I still had oil) : 176 (degree days x home oil coefficient)
Current cost of oil x gallons needed/used = 2.98 x 176 = $527 worth of oil to heat the home last month
Electric bill was $231 this month, minus $105 (base cost of house usage with no heating/cooling) = $126 to heat using geothermal
Comparison vs. oil = $401 saved vs oil heat.

November 09 savings : $150
December 09 savings : $370
January 10 savings : $401 - running total: $920

Can someone tell me if this is correct.

I now heat with propane at a cost of $2.60 a gallon. I used 100 gallons last month to heat with at a cost of $260. At 90,000 BTU per gallon that is 9 million BTU's. I am not taking the efficiency of the gas furnace into consideration.

I am looking at putting in a geo unit with an average COP of 3. To generate 9 million BTU's with this system I would use 659 kw worth of electricity at cost of .105/KW for a total of $69.

Is this pretty close or am a leaving something big out of the calculation?