Purpose of Shut-off valve going to Heat pump?

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danwas44

Member
May 28, 2023
22
Andover, MA
Hi,
I have a question on the plumbing going to my heat pump. There is a shut-off valve in-between my heat pump and the filter. When the pool company installed it they said to leave it half opened. What exactly is the purpose of that. My heat pump can handle up to 70 GPM, but i feel like this valve restricts water going to the heat pump. Here is the photo.
IMG_7440.jpegIMG_7443.jpegIMG_7442.jpeg
 
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That is a bypass valve to limit the flow through the HP to below 70 GPM.

What pump and filter do you have?

If your HP runs fine and heats your pool I would assume the installers set the flow into the HP correctly.
 
ajw22 said:
That is a bypass valve to limit the flow through the HP to below 70 GPM.

What pump and filter do you have?

If your HP runs fine and heats your pool I would assume the installers set the flow into the HP correctly.
Click to expand...
I have a Intelliflo VSP THP 3.95 pump, and a Pentair FNSP-60. My HP runs and heats the water, but I'm concerned it's not efficient. When I run my pump to the max at 3350 RPM, I'm only pushing 49 GPM through the system. I'd prefer it to be pushing maybe 60 or 65 GPM through the HP to maximize the efficiency. That way I'm heating more water with the same wattage in the HP. Does that make sense? A key assumption I have is that as soon as the HP is running, it costs the same to run 20 GPM and it does running 65 GPM....
 
danwas44 said:
I have a Intelliflo VSP THP 3.95 pump, and a Pentair FNSP-60. My HP runs and heats the water, but I'm concerned it's not efficient. When I run my pump to the max at 3350 RPM, I'm only pushing 49 GPM through the system. I'd prefer it to be pushing maybe 60 or 65 GPM through the HP to maximize the efficiency. That way I'm heating more water with the same wattage in the HP. Does that make sense?
Click to expand...

Nope. Your HP puts out a fixed amount of BTUs.

The water at 49 GPM will get hotter then water at 60 GPM. Either carries the same amount of heat to the pool.

Slower water flow has less wear on the heat exchanger.
 
ajw22 said:
Nope. Your HP puts out a fixed amount of BTUs.

The water at 49 GPM will get hotter then water at 60 GPM. Either carries the same amount of heat to the pool.

Slower water flow has less wear on the heat exchanger.
Click to expand...
Interesting, my HP is rated at 118k BTU's at peak efficiency. I was unaware. So your point is the HP puts out the same amount of energy no matter the flow, so lower flow (less volume to heat) = warmer water, higher flow (more volume to heat) = less warm water (in total, same heat into the pool). Awesome, that makes sense.
 
The purpose of the valve is to bypass any flow over 70 GPM.

So, it depends on the pump speed and how much flow you have.

If the total flow is over 70 GPM, then you open the valve some to bypass any flow over 70 GPM.

If the flow is under 70 GPM, you can keep the valve closed.

The problem is that when you open the valve, you don't know how much flow goes to the heater and how much goes through the bypass valve.

I would keep the flow at about 25 to 30 gpm when heating and keep the bypass closed.
 

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JamesW said:
The purpose of the valve is to bypass any flow over 70 GPM.

So, it depends on the pump speed and how much flow you have.

If the total flow is over 70 GPM, then you open the valve some to bypass any flow over 70 GPM.

If the flow is under 70 GPM, you can keep the valve closed.

The problem is that when you open the valve, you don't know how much flow goes to the heater and how much goes through the bypass valve.

I would keep the flow at about 25 to 30 gpm when heating and keep the bypass closed.
Click to expand...
James,
I've tested all my low thru high RPM's and the most GPM was 49. Base on this information, I will shut the valve off. Thank you...
 
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That is really low flow for that pump.

The Caretaker 5 port in-floor cleaning system will create a lot of backpressure, so that can be part of the issue.

Check the inline screen to the Caretaker.

What is the pressure reading on the Caretaker valve gauge?

 
JamesW said:
That is really low flow for that pump.

The Caretaker 5 port in-floor cleaning system will create a lot of backpressure, so that can be part of the issue.

Check the inline screen to the Caretaker.

What is the pressure reading on the Caretaker valve gauge?

Click to expand...
Screen was cleaned out prior to these latest readings in my spreadsheet. I do think it's the Caretaker system that is causing the low flows as the only other outflow is to the leaf trapper.
 
Based on this, I would run at about 2,000 RPM and 28 GPM for the best performance and value.

img_7445-jpeg.497669
 
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