geothermal heat pump

[mosquito]

We are replacing our geothermal heat pump and in reading up on them, I found some information that says you need at least an 80 gal pressure tank. Does anyone know if this is correct?

[speedbump]

Do you mean your replacing the pump that provides water to your heat pump?

If so, tell me what pump it is. The horse power, pump model and the depth to water in your well.

With a ground water heat pump, the unit usually uses much less water than the pump can provide. This cycles the pump constantly while the unit is running. To prevent this you can go with a small 40 gallon tank and the Smart Tee. This will make your pump last a lot longer.

bob...

[toolaholic]

why are you trying to re-engineer the system? sounds like trouble

[mosquito]

What we have is a geothermal open loop heating and cooling system that uses the well for its water source. It is about 25 years old and needs replacing. "they say" that when running, a geothermal unit goes through 6-10 gpm. I can see where a larger pressure tank (ours is a 32 gallon) might be advantageous, but I don't know if its necessary. (I sure could use that $500+ elsewhere in my bathroom remodel!)

[speedbump]

It all boils down to how many pump motors you want to buy in the next few years. Because at 6 to 10 gallons per minute, even a pump as small as a 1/2hp submersible pump will over pump the heat pump and cycle the motor to death prematurely.

That's why I mentioned the Smart Tee. It will prevent that from happening.

bob...

[Bob NH]

Before you change the equipment in a complex system like a geothermal heat pump system, you should understand how the system works and why each part was selected, and the performance characteristics of each part. An important part of owning such a system is to understand it or be willing to pay someone you trust to understand it for you and make recommendations to you that aren't affected by what they want to sell to you.

For example, do you have a diagram and operating description of the system? Do you know the flow rates in the system and the characteristics of the pumps? Do you know the capacity of the heat pump system?

Some geothermal heat pump systems use a pump to bring in the water from a well and reinject it to the aquifer. Others have a buried heat exchanger with a circulator, and the only head loss is in the pipes and heat exchangers. If you have to waste the head in a control valve, you are wasting some power, which may be necessary if the water table is very deep or you don't have a means of recovering the pressure energy. If it is a system with an underground heat exchanger, you will have completely different pumping requirements than if you are pumping water from a aquifer.

If you are replacing a pump or the whole system, you should start with finding out the design characteristics of the pump and other parts of the system. Unless you understand the engineering principles and characteristics of the system, you shouldn't change any part of it.