Is there such a product that uses a geothermal heat pump with a gas booster unit.  I know there are electric ones, just wondered if gas is ever used.

Thanks

Paul

A split type GEO unit can be used with a gas furnace if that's what you mean by gas booster.

From what I understand, with certain configurations you cannot use the geothermal system simultaneously with the furnace, and with certain configurations you can. I am unsure as to why someone would want to run them simultaneously anyway since furnaces run so hot that they don't need a boost from the geothermal system.

During a power outage, a furnace would come in handy if you want a smaller generator compared to a larger one that may be needed to power a geothermal system. Aux electric heat may be a good boost for the geothermal system when outdoor conditions are extreme. Electric heat would also be effective, but expensive to run, for emergency heat should the geothermal system have a problem and lock out. A furnace may be cheaper to run for emergency heat.

Thank you for your answers, yes the booster I refer too is a gas furnace of some sort. As you know geothermal takes a resonable time to respond to fast temperature changes and so the furnace would kick in to get you there faster, so you may have both running together. Do any of you know who makes an integrated system, or are you assuming they are completely seperate systems jointly coupled at the ducting? Would the fan sit in front of the two systems I wonder? If so how would you stop cold air being sucked into the ducting if say the gas was not required? The ducting and fan seem to create issues. Hmmm the plot thickens!

If the system is properly designed and installed, you won't need a back up system for more than 50 or so hours a year. The simplest backup is to go with is electric as it will operate seamlessly with your geo. If you go with gas, it is usually one or the other. They can't both be on at same time.

It would be interesting to run the numbers on using gas instead of electric aux heat. I would expect the best cost point to be with a smaller geo system than the ~95% often used.

Right now in my area LP gas and electric cost about the same per BTU.

I'll bet that's common. LP is a convenient but not particularly cheap source of heat.

The only difference is that for every BTU coming from electricity it takes another 2-4 BTUs out of the ground.....

There's no contest between burning propane at 90% eff and operating a geo with electricity at 3.0+ COP.

My comment above was directed at choosing between operating electric strips for additional heat on top of a geo unit's output vs specifying propane for that purpose. Propane may compare well with strips, but the additional cost and complexity may not be justified since aux heat should only run for a few hundred hours max per year to bolster a good geo system

Exactly. There is also no contest between using 100% geo and < 100% geo with some type of aux heat (the latter wins). Depending on rates, geo system size and the gas used, the best form of aux heat may be arguable.

Paul,
Do you have a gas hot water heater? If so, you could use that indirectly with your GHP as a booster. I have done this with my GHP. I merely pulled out the electric backup unit in the GHP and replaced it with a hydronic (hot water) heat exchanger. It slips into the plenum above the GHP and is plumbed into my gas fired hot water heater. I have a small cir pump inline and the system works great. It's not very expensive to install if you have some plumbing knowledge. Let me know if you want additional info on how it works, I'd be happy to share.
RJDalga
Kzoo, MI

rj, how do you avoid stagnant water problems when not in heating season? Also, is resistance an issue with adding an additional heat exchanger?

Geome, You can avoid stagnant water in a couple of ways 1) periodically run the circ pump for a few minutes (a few times during the off seasons) or 2) remove the heat exchanger during the off season and close the loop (probably should run the cir pump a few times again). Resistance will be slightly higher but if you have an ECM blower then no worries (but this is why I opt for option 2). Hope this helps.

Posted By geodean on 06 Feb 2010 09:07 PM
If the system is properly designed and installed, you won't need a back up system for more than 50 or so hours a year. The simplest backup is to go with is electric as it will operate seamlessly with your geo. If you go with gas, it is usually one or the other. They can't both be on at same time.

10k people in my area have been without power for over a week now due to the snowstorms we had.   A hybrid system that combined a geothermal system,  a gas fired system connected via duck work and a small back generator would be very useful in this instance. Probably expensive to implement, but doable.