i need to size the pump for a heat pump slinky, the slinky is 250meters long and is, 22mm internal diameter and i need 30liters a minute flow of water. how do i calculate the size of pump i need for this , maybe id be better off with a bigger pipe? is there any guidance out there?
In addition to the tables I just posted I would comment:
30 litres/min (=3D0.5 litre/sec) in a 22mm pipe would flow at 1.5 m/ s. That is fast enough to be rather noisy. Generally IIRC one should keep the flow velocity less than 1 m/s for it to be quiet. But maybe that doesn't matter.
Also, the pressure drop will be 1000 Pa/metre and therefore 250,000 pascals for your 250m loop. That's over 2 Bar!
A Grunfoss alpha2 circulator develops a pressure of about 35,000 pascals at 0.5 litre/sec. So cleary you need a bigger pump than that!
For what it's worth - we have 6 x 100m of pipe in our heatpump installation - and it's piped in black 'alkathene'-type pipe with 1" outside diameter as far as the manifold - where it splits out into the six separate loops, each in its own trench.
The advantage of this (apparently) is that, in the event of one loop springing a leak it can be isolated at the manifold without needing to dig up & fix the whole groud-loop.
Our system (Hautec) came with the ground-loop pump pre-installed within the cabinet - are you sure that your system isn't the same ??
Havn't checked the calcs but I would second those comments. I pump water from a spring to a holding tank (for my horses). I have 100 metres of 25 mm pipe and I get 30 litres/min using an eBay 2 inch chinese pump with notionally a 5 HP petrol engine.
In addition to the tables I just posted I would comment:
30 litres/min (=0.5 litre/sec) in a 22mm pipe would flow at 1.5 m/ s. That is fast enough to be rather noisy. Generally IIRC one should keep the flow velocity less than 1 m/s for it to be quiet. But maybe that doesn't matter.
Also, the pressure drop will be 1000 Pa/metre and therefore 250,000 pascals for your 250m loop. That's over 2 Bar!
A Grunfoss alpha2 circulator develops a pressure of about 35,000 pascals at 0.5 litre/sec. So cleary you need a bigger pump than that!
Robert
Does it matter that the fluid is in a loop? i.e. i am just circulating the water/antifreeze around a circuit of pipe?
A rule of thumb was for starters to select a pipe size to give around
200 Pa/m pressure drop in straight pipe. You need details of all the hydraulic resistance of all the fittings in the circuit. The heat pump will have a heat exchanger which could be minimal resistance (tube-in-shell) or a major contributor to the resistance (brazed plate heat exchanger). Pressure losses for the pipe and swept bends will be on the manufacturer's website. The anti-freeze does affect it, it is usually more viscous (propylene glycol although it may be methanol in this application) and reduces the capacity of any given pump.
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