Connecting GSHP to zones

Vince_4

Here the design temp is -19 degrees, but it only occurs 1-2 weeks per year. The average temp is closer to 0 degrees. I'm finding that it makes more sense to size the GSHP for about 70-80% of the load and then supplement for the remainder. Also, if you add an air handler for cooling, the cooling efficiency for the summer is much better with a smaller GSHP. It runs longer and dehumidifies the air more. The electric rates are reasonable using the slab with a dual heat source, which qualifies for off-peak rates.

Vince_4

Connecting GSHP to zones

Looking at plumbing a ground source heat pump with a supplemental electric boiler for a basement slab radiant heat system. Up to this point, installations I've been around have been sized for GSHP to supply full load. Has anyone come up with a preferred method for adding supplemental heat, primary/secondary loop, parallel or other? The way I see it, the simplest route would be to tee the GSHP and boiler into a buffer tank, then draw from the buffer to supply each zone. GSHP would supply bulk of heat, boiler would start if load exceeds GSHP on cold days. I've also been looking at the primary/secondary concept discussed in a post a couple weeks ago. What are the pros/cons to compare both systems? What methods have worked best for controlling the GSHP and boiler? Aquastat to run the GSHP until demand exceeds supply, then second to start boiler? Is there a better way? Any input would be helpful.

mikea23

we have installed alot of GSHP systems with backup boilers. I have found if you do primary secondary like a multiple boiler system. (Boiler 1 the GSHP boiler 2 the back up) when the conventional boiler kicks in it takes over and you dont get the proper delta T for the heat pump to work well. The last 2 systems i did like this I used a buffertank primary secondary and a tekmar 356 to inject into the loop only when its needed i got my delta t to keep the heat pump happy and keep the backup boilers run time to a minimum it ads up to big energy savings.

Craig Bergman

Why not...

size the heat pump to handle the load? Long term operating costs,and initial plumbing costs, will be lower.

Our systems are controled by an aquastat for the buffer tank. The Geo unit only sees the buffer tank and keeps it at temp. We also set the aquastat a couple of degrees lower than the desired temp. (With the probe on the pipe at the bottom of the buffer, the tanks temp inside at the top will be several degrees higher.)

Here is how we plumb it...

Bergy

mikea23

I always size the heat pump to the load but in my area geothermal has such a bad name people want a back up system. and electric rates here in NY are way to high for any kind of electric backup

vs-ndak

Why water heater

Aren't you showing an electric water heater for a buffer tank? Don't the 3/4" tank fittings restrict flow to the heat pump?

Craig Bergman

Not that much

> Aren't you showing an electric water heater for a

> buffer tank? Don't the 3/4" tank fittings

> restrict flow to the heat pump?

Craig Bergman

Not that much

The 3/4" reduction is a very short distance. That's why we cut about a third of the dip tube off and drill extra holes in it.

Bergy