Geo-Thermal heat pumps

[Chilly807]

Our new house is pretty efficient, about the only real loss of heat I can't do much about is the air exchange system, which we shut down in really cold weather. It has a heat exchanger, but you still lose a fair bit of heat. Normally the air is dry enough here in winter that you really don't need the air exchange for a day or two anyway, we alternate 1 day on, two days off if it's really frigid outside.

You're right about the drop in efficiency at higher water temps, but still pushing 250% even at 100 degree water temp.

Our option for AC in summer would be ductless splits mounted on the wall, but we don't get enough heat in summer that it would be worth the extra cost. We're on a pretty high hill, not many days without a breeze.

Chilly

 

[Redneck in training]

IrvingJ

I attended the NH Home Show a few weeks ago in Manchester and talked to several geothermal vendors. They all told me that right now geothermal can only be used effectively in conjunction with forced-air heat systems. In other words you need the ducts. I have base board forced hot water.
Does this jive with what you know?

Thanks,
RangerCap
aka John
Goffstown

Actually geothermal has better efficiency with floor heating due to smaller required temperature rise. Our heat accumulator is set to 90F while inlet water temperature in the winter is about 34F. Therefore the heat pump has to rise the temperature 56 degrees. With forced air it would have to increase it much higher. The difference in efficiency isn't that large to worry about that though. With forced air you need to install only one system and that is cheaper. With floor heating you need to install AC heat exchanger (fan coil) and associated ductwork.

 

[irvingj]

Well, it finally happened...

I had been researching and preparing for the day when my aging heat pump (geothermal) would die. I was planning to replace it with a Water Furnace unit (thanks to discussions here on TBN, btw!), which has higher efficiencies, the beneficiary of 23+ years of improvements.

Two nights ago I was awakened by the gentle sound of an electric motor trying to start but tripping its overloads. Later that morning, it was confirmed: the compressor had finally gone south.

So begins the replacement process.

Over the years I'd had it, I knew it was saving me money over oil heat (common in this area), beginning with full heating season costs of about $350 back in 1987, ending with somewhere around $600-$700 currently. That's for an 1820 sq ft house, over the whole heating season, from late September through April/May.

Playing with some numbers, it looks as though that machine has saved me about $30,000 in energy costs --conservatively-- over its life.

As I still have the water loop and the ductwork, you bet I'm replacing it with another similar unit!

I'll post results of the process as they occur. Sorry I can't give a cost for the original installation, as it was part of a package deal with the house, but I'm guessing these systems probably have about a five-year payback.

 

[irvingj]

Well, it didn't last as long as my 72 Blazer, but yeah, we'll have a little ceremony when it comes out....

I'm just waiting for cost figures on the new one; hope it's not too bad, but it is what it is. I just hate replacing "appliances." I've already done the water heater and the dishwasher.... the ladies of the house (wife, daughter) are now making noises about a new refrigerator....

 

[QRTRHRS]

I just noticed this thread tonight. Lots of good info for me having three ASHP that suck the KW's big time in the winter such as it is here in South Central KY. For now, I guess I will put up with the electric bills but when these units go south, I just may have to dig up the yard.

Coincidentally with reading this thread, just this morning I was reading the latest issue of Fine Homebuilding. This issue has a short but informative article on heat pumps.

 

[Gale Hawkins]

irvingj do keep us posted. I have two units that died and back on a large window unit. It does OK in the mean time but it cost more to run and without the current air handlers it would not keep the whole house cool.

The old ones were Commandaire but plan to go back with Water Furnace due to the dealer I plan to use this time.

 

[Redneck in training]

To give you some perspective: We heat about 3800 sqft. That includes 1400 sqft somewhat drafty garage heated to 60F. The house is single story, no basement. Walls are R18-20, three pane windows, and good ceiling insulation.

We have Waterfurnace geo-heat pump with a pond loop heating the whole house by a floor heating set to water temperature 90F.
Our heating rate is $0.042/kWh. Our normal rate is $0.11/kWh.
Attached pdf file shows heating power consumption last heating season. We used about 2100 kWh in January at cost $88. In other words we spend more money for lights, TV and cooking than heating I suppose. In addition the DHW is heated by waste heat in the AC season and is therefore virtually free.
We used about 9000 kWh/season at cost $378.
I estimate that we would have to burn about 880 gal of propane in the same season at cost about $2000. Since we have floor heating and also AC we spent about 15000 more than for propane fired forced air unit.
I am estimating that we will break even, depending on cost of propane and electricity in about 10 -12 years. Provided my propane consumption and cost is correct. It isn't only about money. You can't beat floor heating comfort.

If you install forced air unit your installation cost will decrease significantly especially if you reuse the original ducts.

 

[irvingj]

I learned a winter or two ago just how crucial the fan in the air handler is; located in the basement, near wood stove, when the fan went out 2 yrs ago --in the middle of the coldest stretch, of course-- I figured no problem- I got the wood stove!

Except for the fact that, without that fan to circulate air throughout the house, I had no way to get the heat from the woodstove aorund to the extremeties of the house....

Oh well, we survived with the use of some small temporary heaters in the bathrooms. Now I have the fan, but no heat pump. I've set the t-stat at just the right temp, however, so it'll come on periodically to circulate heat from the woodstove around; the compressor's disconnected.

Seems to work, and it's a good thing- this AM it's 35 here and spitting snow! Glad I've still got some wood left! Guess the hummingbirds will be a bit late this year....

Hopefully I'll begin to get some info on the replacement Water Furnace unit from the dealer tomorrow.

 

[Chilly807]

I can't give much perspective on unit costs, our was budgeted for a complete new install including the ground and floor loops.

The only downside I've seen to the system we have is the compressor noise, it's louder than I'd like. Not a fatal flaw, but irritating.

Ladia, have you considered adding an outside temperature sensor? Our control (Tekmar) uses a remote sensor on our north outside wall to tell the boiler control what temperature to aim for depending on how cold it is outside. On a warmer day it adjusts the target temperature lower, and hotter on a cold day. This time of year it's looking for approx. 75 F water temp, and up to 90 F in cold weather. The cooler water temp allows for shorter run times for the heat pump, since it doesn't need the hotter water to keep the house warm.

We also added slab sensors to allow the system to keep the floor warm on a sunny winter day when the house air temperature is boosted by the sun.

Sean

 

[whistlepig]

Our forced air ground loop Waterfurnace cost's 80% less to run in the winter season than the fuel oil furnace at our previous home. We don't have any compressor noise. Just the sound of the blower motor kicking on. And, as Ladia says, the AC in the summer is virtually cost free. Our furnace does have the de-superheater. From what I have read the pond loop/well loop geothermal systems are a bit more efficient than the ground loop system we have.