Calculation of thermal output???

[Nostrum]

It's not inverter driven. I wasn't thinking you were about to slag it off, but trust me that if I do mention the brand, there will be a whole chorus of jeering, telling me it's rubbish. I'm basing this on posts in other threads. Don't think it matters for now, I'll share later if people are interested.

The DT was even higher till I cranked up the flow rate!! The Wilo Stratos Pico has adjustable flow rate, and the screen readout tells me I'm at maximum at 4000 litres/hour.

I've been letting the heat pump run and stabilise, although to be honest, it makes little difference. Seems to start out at a DT of 14 and stay there with outlet temperature gradually rising from 43 to 48 when the thermostat cuts out. I mentioned in another post, that I'm running the heat pump into a buffer tank. Would that result in the stable DT? Why do you think it's high?

Do you have a pump valve you can throttle down to see if it effects the displayed flow rate on the display?

What size pump is it you've installed? Looking at the info, my guess would be a 1-6 which at max would give you a theoretical flow rate of about 4m3 p/hr, or 4000 litres...

 

[Dogsbody]

Do you have a pump valve you can throttle down to see if it effects the displayed flow rate on the display?

What size pump is it you've installed?

Well, as already mentioned, there is an adjustment on the pump to reduce flow rate. When I knock that down, the pump goes quieter and the readout shows a lower electricity consumption, so I guess it's working. The pump is the Wilo Stratos Pico 30/1-4.

But as already touched on, if I reduce flow rate, the DT goes even higher.

 

[joni os]

The maths that arrive at 65Kw is agreed, from data based on flow and temp.
Of the two, temp. is easily verified, even by touch. Determination of flow will resolve the issue.

 

[Nostrum]

Well, as already mentioned, there is an adjustment on the pump to reduce flow rate. When I knock that down, the pump goes quieter and the readout shows a lower electricity consumption, so I guess it's working. The pump is the Wilo Stratos Pico 30/1-4.

But as already touched on, if I reduce flow rate, the DT goes even higher.

If the flow rate was measured then external influences (such as reducing flow through a valve) would effect the displayed flow rate. Adjusting the pump on its setting won't.

According to the Wilo data, the pump you've got won't even perform at the given flow rate, so I'd take that with a pinch of salt.

I think it's also safe to say the heat pump isn't providing 65kw, or a COP of 16 for that matter.

Until you can give more info, you won't get the answers you need. I suspect you have flow issues. I'd also be very surprised if you can get anywhere near an accurate COP unless you calculate the real time flow rate, which again requires info from the manufacturer.

Good luck.

 

[Worcester]

Somethings wrong:

66 lpm is one heck of flow rate

Flow rate: 66.66 litres per minute
DeltaT: 14 C

= 65kW that is one heck of a heat load for a heat pump - in a domestic single phase environment the DNO wouldn't let you connect it...

I would expect and old leaky house of 600m2 for that load... That's one heck of sized house, and the radiators will be filling the walls

Two things sound wrong

1) Flow rate
2) delta T

We install Wilo pumps all the time, and they usually display either watts being consumed or m head.

If the system has been installed to proper standards, then installing a heat meter and electricity meter should be a very simple process. (installing them correctly requires some specific knowledge )

We do that quite often when the client really wants to know what's what.

 

[Dogsbody]

Guys, many thanks. I think it's clear that the flow rate I had thought I was getting is well above the actual flow rate. Thanks for homing in on that.

As an aside, I should say that the heat pump is giving hot water in excess of 50 degrees, and the house is nicely warm via the UFH. (Not running DHW off this system.) So, I'm not unhappy with the system overall, but I am just curious about the actual COP compared to manuufacturers figure. Which is why I didn't initially go into lots of detail about the system. I just thought I would get a quicker answer about the COP calculation that way.

Nostrum: Good guess, in part! Yes, it's a Dream, no it's not a self-install.

So, my next move may be to try to find a heat meter, as someone suggested, since it seems I wont be able to work out an accurate figure using the Wilo display.

I can't work out what is wrong with my interpretation of the Wilo display. I'll check again when it is running. In the meantime here is a picture of it, showing how it displays the flow rate:

I fully accept my figure is wrong. From the pump curves I have seen, (it's a 1-4), I would expect about 1750 litres per hour, given that my head is 1.70 metres? Not quite the same as 4000 per hour......

As to DT being wrong, I'm not convinced. As I mentioned before, the inlet and outlet temperatures seem to be what I would expect.

 

[doitmyself]

I think it's clear that the flow rate I had thought I was getting is well above the I would expect about 1750 litres per hour, given that my head is 1.70 metres?

I assume you have set the head to 1.7 metres. How did you arrive at this?

Which operating mode have you chosen Δp-c or Δp-v?

Is Dynamic Adapt turned on?

 

[quality]

You will find that as the ambient (source temperature) drops that the pressure ratio/lift of the refrigeration circuit increases due to energy input increase and the COP will reduce vice versa

 

[Worcester]

Inlet and outlet temperature may be correct...

If you are running at 50° I hope your not putting that into the underfloor, you'll cook it.

Your underfloor should have a blending / mixing valve on it that mixes the return with the flow to reduce it's temp and also it means that the flow around the UFH circuits won't be measurable from the wilo pump.

In practice when done properly (assume no radiators, or if they are they are correctly sized) the installer should have removed the mixing valves on the ufh manifolds and reduced the flow temperature, the heatpump will work much more efficiently producing greater flow at lower temp than lower flow at highertemp.

 

[Nostrum]

Do you have a copy of the heat Pump output curve supplied by the manufacturers?

It looks as though they only do a 10kw model, I'm guessing this would be at A7-W35? If we can have the above, you should be able to calculate the flow rate.

The consequence of a low flow rate will depend on how the heat pump controls operate. Quite likely it will just continue running at a higher flow temperature and higher fridge circuit pressure,which will over time increase wear on the compressor and reduce efficiency overall.