@david999 I haven't seen glycol in a system for about 2 years if I'm honest. Anti freeze valves all the way for me. Glycol is horrible stuff that makes everything work harder.

If the PWM works correctly the flow would slow down with it getting warmer outside as less heat would need to be delivered. 

Posted by: @transparent

↑

The house temperature gets regulated by the flow in the pipes, not by a thermostat turning the pump on/off. Yuch!

 

Absolutely.  To control house temperature vary the flow temperature (using weather compensation), don't turn the heat pump on/off.  The latter simply guarantees inefficient operation.

Posted by: @ant87

↑

If the PWM works correctly the flow would slow down with it getting warmer outside as less heat would need to be delivered. 

Its not flow rate which controls the amount of heat delivered to the house, its flow temperature.  The amount of heat which the emitters give off to the house is determined by the temperature of the water delivered to them (ie the flow temperature).  The heat pump will then try to match this, but the driving factor is the emitters and thus the flow temperature. Thats why getting the weather compensation curve (which sets the flow temperature) right is so important.

The heat pump can use/take advantage of three variables to match the heat it delivers via the water leaving it to the heat lost by the emitters.  These are flow rate, deltaT, or cycle on/off ratio.  Some heat pumps vary the flow rate (using a pwm pump) to keep the deltaT constant, but by no means all.  For those that done its the deltaT which will change as the amount of heat emitted changes.  Cycle on/off ratio is a last resort when the heat pump cant turn down sufficiently to match the demand. 

In addition the compression ratio has to change so that the amount of heat delivered from the refrigerant to the heat exchanger in the heat pump matches the amount of heat taken away by the water to the emitters.   That is driven (principally) by the measurements the HP makes of its water temperatures.

Posted by: @david999

↑

@transparent it’s not going well, it threw up low flow at start up then went up to 36lpm but now it’s running at 31.8. I went around when they left and adjusted my Trv back to 3 setting but I doubt that would make a difference to the primary which now has a upm4xl pump fitted and a 70watt on the rad system.

does flow increase with it getting warmer and are they about to waste 400 quids  worth of antifreeze tomorrow if they fill it since the viscosity is going to increase and even less flow 

You only require a higher flow rate during particularly cold weather.

The quantity of thermal energy that is being transferred from the heat pump to the heat emitters is determined by the flow rate and the temperature difference (DT) between the flow and return temperature.

Most heat pumps are happy operating with a DT around 5C, but it does not have to be exact, and may vary with the flow rate. The amount of thermal energy being supplied to a home is dependent upon the heating capacity of the heat emitters, the flow temperature going to the heat emitters and the return temperature coming back from the heat emitters, giving the DT across the heat emitters.

If you wish I can provide more detail but I would suggest that you don't get too hung up on flow rate.

Posted by: @derek-m

↑

I would suggest that you don't get too hung up on flow rate.

agree!

@derek-m I hear what you guys are saying however at a start up of 30.8lpm the system is close to a shut down on low flow which it was doing at 29lpm before they attended. They intend to install over 100ltres antifreeze tomorrow which will lower the flow more and likely put me in the low pressure shut down range.

@jamespa I wouldn’t if it will run without low flow errors

Posted by: @david999

↑

@jamespa I wouldn’t if it will run without low flow errors

Fair enough.  Perhaps both @derek-m and I should have said 'I would suggest that you don't get too hung up on flow rate, provided of course its not so low as to trigger a flow rate error"

Glycol, it seems, is like marmite, you either love it or you hate it.  Anti-freeze valves ditto.  There are, as yet, no conclusive arguments either way.

@jamespa samsung want heaters installed if antifreeze valves are fitted and then of course corrosion inhibitor, but I read up on frost valves and antifreeze or transfer fluid as they call it and it’s not definitive.  Although the heat geek hates antifreeze if you buy into him.

In my mind the antifreeze valves vs glycol is a "it depends" question.

If like me you are in the south east where it rarely gets below freezing and you are home with the pump running all winter glycol probably is unnecessary.

Somewhere with a much colder climate or long 'escape the winter' holidays maybe it makes more sense.

Posted by: @david999

↑

@jamespa I wouldn’t if it will run without low flow errors

I would suggest that you check the specified minimum flow rate in the manual.

How large is your system? 100 Litres of antifreeze seems rather a large quantity.

I guess tomorrow I need, or they need to decide if they charge it with antifreeze with such a low flow rate and find it shuts down on low flow. The pump seems to gradually grind the flow up where they want to be, not I but will it cope with antifreeze and simply not run 

@derek-m 16 radiators samsung wanted a 46lpm flow rate on 35mm pipe and seem to be supporting the installer by diluting this down to 36lpm on 28mm pipe. It’s a 16kw heat pump and the first stats are what’s detailed for both that pump and the 13kw.  Flow is everything on a heat pump, to fast and it’s noisy and you get erosion corrosion and too slow it runs inefficiently.