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ASHP failing to reach delta T


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1 hour ago, rhymecheat said:

I didn’t but it was the only one with a design my wife approved (insert massive eye roll). I think over 30kwh/day is wrong as with a COP of over 3 at 45C and 8C outdoor, that would seem like a massive amount of heat. But then the return temperature always stays high which tells me the heat is not leaving the loop or too much heat is being produced 

 

30kWh/day is an average of 4.5kW at a COP of 3 ( think). Depending on the house, that's not unreasonable in January. But you need to check the heat loss calculations.

Edited by Kevm
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Going back to first principles, if the incoming water temp is only just above the outgoing water temp then either the pump speed is too high or youre radiators and UFH are not dissipating the heat properly or the house is up to temp. ?‍♂️

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9 minutes ago, joe90 said:

Going back to first principles, if the incoming water temp is only just above the outgoing water temp then either the pump speed is too high or youre radiators and UFH are not dissipating the heat properly or the house is up to temp. ?‍♂️

The confusing part to me is that most of the day the UFH is on and it says on the manifold that return temp is about 8C lower than incoming water temp so the UFH must be dissipating heat at a good rate. Most of the day. This is the only loop in operation so I don’t get why the heatpump still reads a return so high. 
 

Atm heatpump flow is between 27 and 32l/m (is oscillates). 

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2 minutes ago, rhymecheat said:

The confusing part to me is that most of the day the UFH is on and it says on the manifold that return temp is about 8C lower than incoming water temp so the UFH must be dissipating heat at a good rate. Most of the day. This is the only loop in operation so I don’t get why the heatpump still reads a return so high. 

Get the installer back and pose this question to them.

 

Or check with for example an IR thermometer what the actual flow and return pipe temperatures are at the heat pump.

 

Is there a buffer tank in this system?

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45 minutes ago, ProDave said:

Get the installer back and pose this question to them.

 

Or check with for example an IR thermometer what the actual flow and return pipe temperatures are at the heat pump.

 

Is there a buffer tank in this system?


I’ve checked with a FLIR camera and it seems to match the sensors. Yes, there is a buffer tank, it’s a Cordivari 29W 26L

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2 hours ago, rhymecheat said:


With the old boiler, total consumption for last year was 14890kwh if that helps. 

 

 

I replaced an oil boiler with a heat pump.  My old oil boiler used about 21500 kWh per year's worth of oil (@10.35 kWh per litre) so less than that in actual heat because my boiler was not 100% efficient.  My heat pump used 6900 kWh of electricity in its first year of use.      

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3 hours ago, dpmiller said:

what brand of manifold is it? Some have an adjustable bypass on the supply side that can make the numbers look odd

It’s a polypipe. It’s got a mixing valve set at 35C and gauges for in/out water temperature. 

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Does the reading on the mixing valve match the temp of the water after the valve ? Mine was 15c and I had to take the knob off and move it a few splines to may displayed temp with actual temp.

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The dT across the ASHP flow/return is dictated by flow rate (1800m3 per hour it seems) and energy applied. That’s the only two factors.

 

The heat pump may not run continuously as it’s minimum output maybe higher than the heating system output - particular if there isn’t enough volume of water circulating, resulting in rapid swings.

 

When the heat pump is resting between cycles, the return and flow temps will be the same as no energy is being provided.

 

Is there a backup heater in the system?

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8 hours ago, Fly100 said:

Does the reading on the mixing valve match the temp of the water after the valve ? Mine was 15c and I had to take the knob off and move it a few splines to may displayed temp with actual temp.

Yes, yes it does. 

 

17 minutes ago, J1mbo said:

The dT across the ASHP flow/return is dictated by flow rate (1800m3 per hour it seems) and energy applied. That’s the only two factors.

 

The heat pump may not run continuously as it’s minimum output maybe higher than the heating system output - particular if there isn’t enough volume of water circulating, resulting in rapid swings.

 

When the heat pump is resting between cycles, the return and flow temps will be the same as no energy is being provided.

 

Is there a backup heater in the system?

Indeed there is. I don’t know how long a cycle would be but I’ve monitored the sensors for about an hour straight and never saw a difference of more than 1C, always with the return higher than the leaving

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Maybe there is a fault with it then. If the heat pump isn’t heating the water, something else (that is expensive to run) certainly is. Perhaps you can measure the dT across the backup heater.

Edited by J1mbo
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So, downstairs is currently 17.5C with 0C outside. UFH manifold is receiving 42C and returning about 30C. I’ve used the thermal camera once more and I think I see some clearer issues here. I’ve attached some pics

CCFCC340-5368-4A85-90CB-D625E5ADF865.jpeg

C520AE0E-01C2-47BA-AECB-A1F671BCC2E8.jpeg

64005EF2-D098-4A1C-A478-BACD06E2D75C.jpeg

19EA65FC-CA32-4F8B-9180-43511CAB3BB7.jpeg
these are under new bifold doors. I don’t really know why only the bottom is this cold

 

Same camera is telling me the rest of the floor space is at about 22C for reference

Edited by rhymecheat
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Can we see thermal image pictures of the flow and return pipes into the ASHP.  Assuming they are covered in pipe insulation, remove a section of that for the photos so we can see the actual pipe temperatures.

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3 minutes ago, ProDave said:

Can we see thermal image pictures of the flow and return pipes into the ASHP.  Assuming they are covered in pipe insulation, remove a section of that for the photos so we can see the actual pipe temperatures.

Yes of course. But I’ll have to do that later today as I really don’t wanna open the bifolds/loft in this cold. 
 

Meanwhile, do you think those low temps under the bifolds are normal?

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2 minutes ago, rhymecheat said:

Meanwhile, do you think those low temps under the bifolds are normal?

The doors don't look good.  Bifolds have a reputation for being leaky and hard to make reliably air tight.  But the whole frame looks cold. What make are they?

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12 minutes ago, ProDave said:

The doors don't look good.  Bifolds have a reputation for being leaky and hard to make reliably air tight.  But the whole frame looks cold. What make are they?

I’m not sure unfortunately. They’re from a local company. Owner lives a few doors down the road

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1 hour ago, rhymecheat said:

So, downstairs is currently 17.5C with 0C outside. UFH manifold is receiving 42C and returning about 30C.
...

Same camera is telling me the rest of the floor space is at about 22C for reference

 

Is your UFH on all 24 hours?  If yes and 17.5 C is too chilly for you, can you raise the flow rate to boost the return temperature so the average temperature is higher? 

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7 minutes ago, ReedRichards said:

 

Is your UFH on all 24 hours?  If yes and 17.5 C is too chilly for you, can you raise the flow rate to boost the return temperature so the average temperature is higher? 

I thought the lower the return the more heat was being kept in the room. You’re saying if I increase the flow for the living room zone it should be warmer?

 

edit: yes. Atm the UFH has been on all night and probably will all day

Edited by rhymecheat
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8 minutes ago, rhymecheat said:

I thought the lower the return the more heat was being kept in the room. You’re saying if I increase the flow for the living room zone it should be warmer?

 

edit: yes. Atm the UFH has been on all night and probably will all day

The average water temperature is halfway between flow and return temps. So the average energy transfer to the slab (or air if it's a radiator) is a function of the difference between the water and concrete (or air) temperatures. Higher pump speed = higher average temperature = greater energy transfer.

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44 minutes ago, J1mbo said:

The average water temperature is halfway between flow and return temps. So the average energy transfer to the slab (or air if it's a radiator) is a function of the difference between the water and concrete (or air) temperatures. Higher pump speed = higher average temperature = greater energy transfer.

I see! So let’s say I start increasing the flow. At what stage does it not need increasing anymore? Or should I just crank it up and leave it until the room is warm?

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1 hour ago, J1mbo said:

The average water temperature is halfway between flow and return temps. So the average energy transfer to the slab (or air if it's a radiator) is a function of the difference between the water and concrete (or air) temperatures. Higher pump speed = higher average temperature = greater energy transfer.

 

Strictly it's the rate of energy transfer that counts, the Watts rather than the Joules or kWh. If you increase the pump speed each litre of water going round the loop will lose less energy but you will be sending more litres of water round in any given time so the net effect is to give you more Watts of heat.  

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