ASHP - Pipe size

waqasahmed

Let's say you don't have good insulation 

Could you theoretically still achieve the same low flow temps with oversized pipes, and oversized rads?

Obviously, you should insulate your house anyway, but I was wondering if you'd basically achieve the same COP without having done that?

And then basically having pipes that are already "oversized" so to speak 

Reed_Richards

COP has nothing to do with insulation.  The amount of insulation you have will affect the amount of energy needed to heat your house but this has nothing to do with the efficiency of a heat pump.

The efficiency (and hence COP) of a heat pump (ASHP) depends on the temperature difference between the outside air and the water leaving the heat pump.  If you can keep this as low as possible you will achieve the best efficiency.  You can do that with "oversized" radiators (or Underfloor Heating).  For any give water temperature the poorer the insulation the bigger the radiator you will need for a room of some particular size, if that is what you mean.

You can also boost the heat output from your radiators by increasing the flow rate through them to reduce the temperature drop across the radiator.  This does not require "oversized" pipes but if the pipes are too narrow if may be difficult to achieve the flow rate you want.      

shinytop

Yes, as long as your rads are sized correctly to give off enough heat at the flow temp you want.   COP has nothing directly to do with insulation.  

waqasahmed

Reed_Richards said:

COP has nothing to do with insulation.  The amount of insulation you have will affect the amount of energy needed to heat your house but this has nothing to do with the efficiency of a heat pump.

The efficiency (and hence COP) of a heat pump (ASHP) depends on the temperature difference between the outside air and the water leaving the heat pump.  If you can keep this as low as possible you will achieve the best efficiency.  You can do that with "oversized" radiators (or Underfloor Heating).  For any give water temperature the poorer the insulation the bigger the radiator you will need for a room of some particular size, if that is what you mean.

You can also boost the heat output from your radiators by increasing the flow rate through them to reduce the temperature drop across the radiator.  This does not require "oversized" pipes but if the pipes are too narrow if may be difficult to achieve the flow rate you want.      

Thanks. That's what my impression was too. That's not too bad then, if you're willing to seriously oversize your pipes anyway

Reed_Richards

With radiators it's the bigger the better.  Not so with pipes, they just need to be more than a minimum size.  Typically it is 15 mm to individual radiators, 22 mm feeding multiple radiators and 28mm from the heat pump to the DHW cylinder and buffer tank.