Primary Circuit Pump on heatpump design

[wes123]

Hi clever people

I am new here and hoping a couple of you smart people can help me. Im also sorry if this is a really silly question.
I am trying to create a basic set up of an air to water heat pump system.

for example an 18kw heat pump requires min 0.7l/s with a pressure drop of 60kpa over the heat exchanger. Is it possible that i can put a pump with 6m head with the 0.7l/s directly before the heat exchanger on the return pipework of the heat pump and it will always get that amount or would it also depend on the rest of the system pipework pressure?
Could i create a primary loop with a pressure by-pass to work in this situation?

Thanks
Wes

 

[bimr]

The pump produces water fluid flow. The resistance of the piping circuit and heat pump to fluid flow, creates the pressure.

Consider posting a diagram of your heat pump system to illustrate your question.

 

[Rputvin]

Just because I like working in english units, or at the very least the same units;

0.7l/s = 11 gallons/minute
60kpa = 8.7psi
6m head = 19.7ft = 8.5psi = 58.6kpa

So your chosen pump CANNOT overcome the resistance of the heat exchanger. Yes, we're working with round numbers and conversions, but there is more resistance than just the heat exchanger and you're already coming up short. You're going to need a bigger pump regardless of the rest of the circuit.

But yes, the pump performance depends on the rest of the circuit it's attached to, pressures and flow that's already present, etc.

 

[LittleInch]

a diagram works wonders for letting you figure it out and for us to work it out.

However I agree with Rputvin, your 6m head is only the resistance of the HX at that flow. doesn't leave anything spare for the primary loop and other losses.

If 0.7l/s is the MINIMUM, then if the 60kPa is the resistance at that flow then that's all you'll get through it. what's the Max pressure drop at what flow?

You need to work out how the system works and controls itself. If you're working on primary / secondary system then the mass of the primary system needs to be reasonable so that the temperature doesn't shoot about as flow in the secondary system changes, unless they are fixed flows and heat loss.

but in short, no - you need to work out all losses in a circuit and size your pump accordingly. A 6m @ 0.71 l/sec pump is unlikely to work.

Remember - More details = better answers
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