Geothermal flows and pressure loss - help!

Dave Rothrock

Keith,
Usually the pump sizes and flow rates are determined by evaluating energy costs to operate both the pumps and the compressor, thereby optimizing the entire system. Sometimes pumping a higher flowrate will waste more pump energy than that gained by a lower headpressure on the compressor. You also have to make sure the temperature ranges (and delta Ts) for the source and load sides for your application are suitable. You don't want to trip your compressor safeties.

In your case with the "pump and dump", the source pump energy will vary with both the flowrate and the depth of the water in the well. The required "lift" in the typical open loop system uses more pump energy than the typical closed loop system. Also, depending what you are doing with your discharge, you will not want to waste water, so you are on the right track looking at the lower flow rates. Your variable speed pump should be the ticket for this job.

In heating mode, the source water is cooled in the evaporator, and minimum flow rates are critical to prevent freezing the coil on open loop systems(you will not have antifreeze). Fifty degree entering water is not that far from freezing if the flow rate drops too low. Be careful of your pump start or cut-in pressure to assure the minimum flow rate at worst case condition. The Climatemaster GSW060 has controls which protect against freezing the evaporator. I'm not sure, but I think the Water Furnace unit also has these controls. Make sure whatever unit you select has this feature and make sure it is set for open loop application. Not all units incorporate these controls as standard accessories.

Best wishes with your project!
Dave

Keith McKinley

geothermal flows and pressure loss - help!

I'm looking at a two water to water heat pumps. A Water Furnace EW060H and a Climate Master GSW 060.

My question is regarding the flow rates and pressure drops.

Seems both units list 3 flow rates for the source side and 3 for the load side.
After looking closely at the matrix (my eyes are still crossed) I'm kinda stumped. Ultimately the HC is just about the same across the board when considering three fixed values. The EWT for the source which in my case is 50F well water, the EWT for the load which I'd like to be about 105-110F, and LWT which I want in the buffer tank in the 125 degree range.

I have a constant pressure, variable speed Grundfos well pump (up to 18 gpm) My thinking is that since there is very little pressure loss through the Geothermal unit and I have no huge closed loop system I can run at the lowest flow rate of around 7.5 gpm. Additionally, the plumbing to the buffer tank is also negligable and although I don't know the pressure drop through that heat exchanger, I'd say I should be able also run at lower gph which should help with getting the most heat transferred to the buffer tank?

Am I way off here from my HS physics? What are the considerations for using the GPM figures and pressure loss on the load and source sides. I'm assuming its for pump sizing and piping issues and maybe Delta T for the geo unit.

Also I can't find any numbers regarding the entry water pressure on the source side for the geo unit. I run my pump at 50 psi but obviously could put a pressure reducer on the source to the geo unit. My guess is pressure is no issue in this regard as long as the flow rate is set properly.

This is worth a beer!

Keith