Calculation of thermal output???

[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.

 

[Dogsbody]

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?

My figure of 1.7 m is the measured height differential between the pump and the highest point of the circuit, the inlet to the buffer tank. Did I need to look at something more subtle?

I have not actually set this into the Wilo settings because if I do, my DT shoots up even higher and I eventually get a "Flow Rate Error" on the heat pump. At the moment I have the head set to 4m, (the maximum), and this stops the flow rate error message and gives me a DT of 14C.

I have Dp-c, which is what they recommend for UFH?

No sign of Dynamic Adapt in the instructions or on the display!

 

[Dogsbody]

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.

Guys, thanks again to everyone who is taking an interest. Sorry if I'm not responding to every post, but there seems to be some sort of lag where I reply to one post, and then see there was another earlier one that needs a reply. Or perhaps I'm just being confused by all the various posts and questions.

I don't have a heat curve, I'm afraid. It is claimed to be a 15 kW model, I think at A7-W40.

How can I reduce the DT? I cannot increase flow rate any more unless I get the more powerful circulation pump. Ambient air temperature around the heat pump is about 12C at the moment.

 

[Dogsbody]

Worcester: The water goes into the UFH at around 40C.

 

[doitmyself]

My figure of 1.7 m is the measured height differential between the pump and the highest point of the circuit, the inlet to the buffer tank. Did I need to look at something more subtle?

It's much more subtle than that.

Head has nothing to do with measuring the distance between pump and highest point. (I have even read post from "pro's" who didn't know this.) The head of a system is the pressure loss round the circuit due to friction caused by the water flowing. The pump has to overcome this loss and provide the required flow rate. I suspect that your pump may not be able to do this.

Stating the head in metres (of water) is an antiquated way of doing it. The better way is to quote the pressure loss in Bar or kPa.

Wilo recommend ΔP-C for a UF system, so stick with it.

What is the design temperature differential of the UF system?

How was the pump size determined?

 

[Nostrum]

If we assume that the heat pump is delivering 15kw, which given the outdoor temperature is probably fairly close, and with a DT of 15. We get a flow rate of 0.31 ltrs/second or 1130 ltrs/hr.

From what little information I can find on this heat pump, the specified flow rate is 2.2m3/hr, yours is 1.13m3/hr.

You've already stated the pump is on maximum, so we have to assume the flow rate is due to frictional loss within the circuit.

How is the heat pump piped in relation to the buffer? A picture would be the best way of showing this.

Worryingly, the pipe connections specified on this unit appear to be 3/4".

 

[Dogsbody]

OK, I had a nasty suspicion about the way to measure the head!! So, we don't actually know what the head is. No way to know without installing more kit, I'm afraid.

But in any case, can we take a small step back? We seem to have decided that the flow rate is too low. Why do we think this?

 

[rpm]

You've already stated the pump is on maximum, so we have to assume the flow rate is due to frictional loss within the circuit.

How is the heat pump piped in relation to the buffer? A picture would be the best way of showing this.

Worryingly, the pipe connections specified on this unit appear to be 3/4".

These will effect the flow rate.

 

[Norcs]

How do you lower the condensing temperature on a modern A-W heat pump?
Is this factory set?

 

[Dogsbody]

These will effect the flow rate.

Well, I appreciate that. But why do we think there is a problem with the flow rate? I was getting a low flow error message. I turned up the flow. I no longer get the message. Therefore there is no problem with the flow rate. ......I'm being deliberately simplistic.

I'd just like to know why some posters think there is a problem.

 

[quality]

15Kw air source on single phase is ambitious, if your happy then that's a bonus

 

[Dogsbody]

If we assume that the heat pump is delivering 15kw, which given the outdoor temperature is probably fairly close, and with a DT of 15. We get a flow rate of 0.31 ltrs/second or 1130 ltrs/hr.

I don't understand how you get that flow rate, but I assume you know how to do the figures. On the other hand, can we rely on the 15 kW manufacturers figure if you are basing your result on that?

If the flow really is as low as 1.13 m3/hr, why does the heat pump not throw up an error message if it needs 2.2 m3/hr as you correctly point out?

 

[Nostrum]

With respect, given the very little detail we have of both the heat pump and the installation, we can't rely on any of the information in this thread.

You've got a multitude of people giving you their time for free on here with the hope of answering your questions and potentially finding a fault on the system, yet you seem reluctant to give any more information then you need to for fear of possibly being told something you don't want to, at a guess?

The reason the heat pump requires a high flow rate is partially due to the load on which the compressor and fridge circuit is being put under. The harder it has to work the higher the pressure in the fridge circuit will be. Too high and the heat pump will throw a fault, but that's not to say that it can still be running at an elevated 'unhealthy' level but below the fault trigger.

Either way, you're making it too hard for anyone to further help you, so good luck but I'm out.

 

[Dogsbody]

OK Nostrum, sorry you couldn't help. Your last post is a classic example of why I don't want to furnish loads of detail outside the scope of my original post. People just ignore my question and go off at tangents. At the point we've reached, I just have one simple question. What makes anyone think the flow rate is too low? I don't need a lesson on why it is bad for it to be too low. I'm just trying to point out that we seem to have slid into a debate about my flow rate being too low, when I don't think that has been demonstrated. Obviously "too low" is a relative term anyway.

Bear in mind, I need to keep it simple as I'm a homeowner, not a professional.

Thanks for trying anyway.

Anyone else, or shall we close this off?

 

[Nostrum]

The answer was in post #12.

 

[Norcs]

15Kw air source on single phase is ambitious, if your happy then that's a bonus


But that will likely be the output after being multiplied via the compressors compression cycle which will be using about 3 or 5 kilowatts max?

 

[Dotty]

Adequate answers have been given.

Thread closed.