Geothermal heating system and extreme temperatures.

[doxford jim]

Hi Guys,

I just tried posting a thread but lost it for whatever reason - so if it is duplicated you will know the reason why.

I am interested in electricity consumption for a geothermal heating system in extreme conditions.
I have a 5 ton WaterFurnace unit with horizontal lines buried outside at 7ft or 8ft (previous owner information). I keep a 2,000sf house at 68F - also the 950sf basement and the 900 sf double garage (closed off to outside).

We are just starting to get winter conditions now around here where I live - last night at -24C/-10F and today at -18C/-2F. For the last twenty four hour period we have used 95kWh of electricity keeping the house warm. There is no gas usage except for the back up propane furnace, so that is all the energy used.

I had an energy meter installed that gives me the power usage every 30 secs. or so, as it is being used. I also log daily consumption as I do not trust our utility company - they have tried to screw me a few times with their "guesswork" consumption billing.

Would be interested to know what other owners are getting for similar conditions. Our winter temperatures can drop as low as -40C. Of course house insulation makes a big difference, but I believe our house is fairly well insulated, so a comparison would be usefull.

Thanks in advance, for any other owners info - would help to understand house heating efficiency.

Thanks

jim

 

[MacLawn]

Well, dox, a few boys here are using geothermal, so they should chime in soon. I'm very interested in their replies, because even here in Georgia, we canno' stand even our cold! We have regular heat pump and a great Buck stove fireplace, but geothermal is our next want for our house. Hope yours works good in REAL cold.

 

[bcjmmac]

Hi
I have a Waterfurnace Geothermal Synergy unit, installed when we had the house built in 2010 - not sure of the size & am on the road so can't check but believe it is 4 ton, maybe 5, HVAC with a de-superheater to help provide hot water. House is a colonial center hall plan, 2640 Sq Ft above ground, 1400 below, 2x6 construction built to R2000 Canadian standards - energy efficiency rating of 87. We have 4 vertical wells/loops & a very high water table so no issues with energy transfer.
Last month's bill was $123 Cdn, which includes a $22.50 service charge. Rate is 10.25cents/KW. We live in the country, so that includes the water pump, hot water, etc. Summer, with AC on a few times a week, bills run $70 - $80.
Highest bill we have ever had was ~$250 during a very prolonged cold snap last winter; -20 or lower with high winds (almost always windy here in the Maritimes/close to the gulf of St Lawrence).
1 thing to be aware of - never raise the thermostat more than +1 degree at a time or the aux heat will come on. Aux heat is just a fancy way of saying supplemental electric heat. Our unit has a rating of 4.5, which equates to $4.5 of heat for every $1 of electricity. Aux heat is of course $1 of heat for every $ of electricity, assuming 100% efficiency.
Note; aux heat is intended to supplement the geothermal unit when it is too cold for the unit to handle the heat loss so is designed to come on if the house temp falls more than 1 degree below the thermostat setting. You can confirm this on your unit by checking the thermostat - if you raise the temp by 1.5 degrees the aux heat symbol will come on.
Love the unit - only need to change the filters regularly for maint. The comfort level is great & it is very quiet - you have to put your hand/foot on top of a vent to notice it is on.

 

[dodge man]

I just had geo installed about 2 months ago. I'm not sure what my usage for a day would be. My house is 1900 sf with a full basement, new windows, probably average insulation. My geo is a 4 ton.

I can see what the actual usage is. On stage one it's using 2100 watts. On stage 2 about 2600 watts and I'm not sure what stage 3 uses. Stage 1 & 2 are all geo, stage 3 is electric. I'm not sure on the math but I think if mine ran for 10 hours a day , that would be about 22 kWh. I'm pretty sure it hasn't run 10 hours a day yet. I have a separate meter for the geo bot I haven't paid attention to it yet.

Your numbers seem high, but your house is bigger and the temps colder so they may be reasonable.

 

[doxford jim]

Thanks for the comments so far.

From what you lot say, the cost of my heating seems high - maybe there is another problem I am not ware of. The house insulation isn't bad but could be improved of course - something I will check out this coming summer.

The energy meter I am using has proven to be an eye-opener in what power is used. The outside temperature now, as I write, is -28C/ -19F and the power being used for heating is 8411 watts or 8.4kW. At this rate there will be a lot of power used. The house sits on top of a hill and although somewhat sheltered by trees, still experiences a lot of weather.

The meter I am using is the MTP3100 and shows actual usage as it happens. It is an eye opener as to what power is being used.
As I write this I am starting to think that my place is not as well insulated as I had previously thought.

If anyone else has examples of what power their system uses I would appreciate knowing.

September and October of this year, 2706 kWh of electricity were used over 59 day period and cost me $292.94 or $150 month. November and December will likely be twice that amount with the total bill being around $600. I do know the natural gas is expensive in this area as is propane for heating. I was told by a neighbour that they paid around $200 to $250 a month for natural gas for a small house (less than 1,000sqft). Of course prices vary from province to province and state to state, but the general thought is that geothermal should be 50% or more, cheaper than gas or other heat. In my case I am not so sure and with the current price increases in BC, the advantages seem to be going out the window.

Talking of windows, do any of you have triple pane windows ? I am thinking of adding a third outside pane to existing windows to cut down on heat loss. Hopefully that will make a difference in power used. Has anyone else done this and if you have, how effective was it ?

Thanks and please keep the info coming as I am sure others will find this of some help.

Cheers

jim

 

[dmccarty]

Thanks for the comments so far.

From what you lot say, the cost of my heating seems high - maybe there is another problem I am not ware of. The house insulation isn't bad but could be improved of course - something I will check out this coming summer.
...


Thanks and please keep the info coming as I am sure others will find this of some help.

Cheers

jim

One thing you have to consider is what temperature people keep their house. I am always amazed at the low temperatures some TBNers have for their house during the winter and summer. :shocked: My wife would freeze to death at the temperatures some TBNers keep their house! :laughing: Both in winter AND summer!

Later,
Dan

 

[buckeyefarmer]

lots of factors come into play in designing a system. Design software uses bin temperatures, i.e. the number of hours per year your temps fall into a temp range. So, if historically you might reach -40, but it might only happen for 1 or 2 hrs per year. Other areas, the lowest might be 0, so the design is different. Also every house is insulated different, the windows have different R values, etc, so that all goes into the ManualJ calculation that is used to size your unit.

 

[SPIKER]

Those Water-furnaces are some of the best (most efficient) ones going them and some other company are competing all time for top rated two. Other than that I say see if you have a local HVAC contractor who can do a HEATING audit. Use air fans to put seal on house and pull in cool air an use a IR camera to find the leaks.

Mark

 

[dodge man]

That's using a lot of power, I'd say that's using electric not just geo, probably because it's so cold.

 

[MacLawn]

I'mm with you Dan, man, we freeze in our Georgia winters! Me old bones just cain't stand cold weather. I was born for the tropics. We keep our house 73º-75º in winter, about 73º in summer - and drive old cars and trucks. I'll put me lucres into staying comfortable at home, where I belong. I'm really wanting to check into geothermal too, IF it will keep us warm in winter and cool in summer.