@bontwoody Thanks, I hope you have a lovely evening.

Posted by: @johnnyb

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I have tried different speeds on my pumps but with some the pump switched off and others the deltaT just got smaller, down to 0.5 at one point and then the pump switch off.  With a low flow temperature deltaT gets a little smaller I think, but mostly it is around 1.5-2, it is set to 5 in the settings and that is what it gets to with a DHW cycle.

I think the low dT is a consequence of the low flow temp you are trying to use, 1.5-2 is small but although a dT of 5 is often cited as optimum, i dont know of any reasoning behind this. Why your pump turns off I cant really fathom.

Posted by: @johnnyb

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Did the PWM pump make much difference to your COP and help things run better, was it worth changing?

I think it has, initially I bought the wrong pump model which didnt have PWM control, so was umming and arring as to whether to switch, but Im glad I did. I can see the pump flow changing as the heat pump requires and this allows it to create a steady dT of 5. So this might well help you.

Posted by: @johnnyb

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I have several more questions after reading your blog, it looks like you set your up yourself? There are several settings I would like to try adjusting but I don't want to cause any issues or lose track of what I have changed and what affects they are having.

I did install it myself, the Glyn Hudson Youtube videos are great so It wasnt that hard. As long as you record your initial settings you can always revert back if something doesnt work.

Posted by: @johnnyb

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The field setting value (FSV) 4051 on my system is set to Use(100%). You said you had to change yours to off for your pump to stop running continuously on the original pump. My pump doesn't run continuously but I wonder if that is affecting my set up. Did you change both the positions of the wires and the setting at the same time? I would assume you did and don't know if the setting made the difference or the cable positions

Yes, I changed both at the same time to allow the new pump to function using PWM control

Posted by: @johnnyb

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When you had the cycling with the low flow temperatures was it affecting the COP? I don't think mine cycles, the primary pump is always on and I think the outdoor unit is always running when the pump is but haven't sat beside the outdoor unit to watch it as it is wet and windy today. I also think that with FVS 2091 set to Use (signal on/off) it stops the unit cycling, but I'm not sure if I have understood that correctly or not, it might just be the primary pump.

Im not absolutely sure that cycling seriously effects COP, but the percieved wisdom is that its not good for the compessor on the heat pump and can lead to premature failure. The FSV 2091 setting is a bitch. Here is a useful resource https://community.openenergymonitor.org/t/i-want-to-punch-my-samsung-controller-fsv-2091/27143

Posted by: @johnnyb

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It looks like you had the flow at low 30's in your graphs, but said you'd set the water law temperatures at 38 to 45. Do you find the flow temperature is several degrees lower than you have it set in the waterlaw temperatures, mine seems to be.

Ive played around with my water law settings constantly as I improved the house currently they are 33C at 17C OAT and 39 at -2. I dont find that my flow temperature is lower than the set point, you do I think because of your buffer. Hot and cold water mixes in a buffer reducing the output flow temp. You have to run the input flow temp higher to counteract this and thats why buffers should be avoided if at all possible. Installers like to use them because there are no flow rate issues for the pump, but its a hit to efficiency. The fact you have UFH and rads may complicate things but if you can get rid of it, you should.

Posted by: @johnnyb

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DO you know what the settings need to be for the Samsung display unit to acts as the thermostat and control the heating? I have an external thermostat fitted but want to try using the Samsung controls as you have done to see if it works, the thermostat I have seems to have a mind of it's own. I found settings somewhere online but when I tried changing them a couple of days ago the secondary pump didn't switch on.

See the OEM link above:-)

Posted by: @johnnyb

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I love your EV. We looked at the i3 several years ago, and loved it, but bought an e-Golf as VW had a great deal on back in 2017 and the price was about £10k cheaper. We still have it, but look at i3's and still think they look a great little car.

We love it too, but its our first EV so dont really have a lot to compare it to. EVs go together with heat pump like cheese goes with wine 🙂 Im using the Octopus Intelligent Go tariff and a small battery, our running costs are small!

Hope that helps 🙂

Posted by: @technogeek

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@johnnyb If it is any help, I calculate the COP / SCOP using the following formula for my Samsung heat pump

 ( Energy Generated + Energy In ) / Energy In = COP

This is what I've assumed for my Vaillant heat pump and it's definitely the basis of their efficiency number. However, it's got me thinking. Does all the energy used by a heat pump get transferred to the fluid heating the building or is some (eg heat losses from the motor) lost to the environment (but may slightly warm up the air around the heat pump)? It should be possible to figure this out by monitoring the heating of the DHW where a known volume and temperature rise needs a calculable amount of kWh, but is a single DHW temperature sensor good enough to reflect what's happening in the cylinder.

Also, if the heat pump is reversed for cooling then will the energy used have a negative impact on the efficiency?

Posted by: @johnr

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Posted by: @technogeek

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@johnnyb If it is any help, I calculate the COP / SCOP using the following formula for my Samsung heat pump

 ( Energy Generated + Energy In ) / Energy In = COP

This is what I've assumed for my Vaillant heat pump and it's definitely the basis of their efficiency number. However, it's got me thinking. Does all the energy used by a heat pump get transferred to the fluid heating the building or is some (eg heat losses from the motor) lost to the environment (but may slightly warm up the air around the heat pump)?

 

No process is 100% efficient, so yes some is lost from pumps, electronics, pipework etc.  I think Vaillant monitor deltaT and flow rate to calculate energy delivered and if so most of this is accounted for other than losses in pipework or other fittings between the heat pump and the house.

Posted by: @johnr

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It should be possible to figure this out by monitoring the heating of the DHW where a known volume and temperature rise needs a calculable amount of kWh, but is a single DHW temperature sensor good enough to reflect what's happening in the cylinder.

See above for how I think Vaillant calculates energy delivered.  It can tell whether its delivering to house or DHW from the state of the diverter valve.

Posted by: @johnr

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Also, if the heat pump is reversed for cooling then will the energy used have a negative impact on the efficiency?

 

Energy efficiency for cooling is measured as EER which is ratio of cooling output to input power.  'Lost' heat, if it finds its way back to the refrigerant, presumably does impact negatively.  It may well be that heat pumps optimised for heating and low noise (with a compressor that is insulated) are less efficient at cooling than those optimised specifically for cooling!  I dont know this for a fact, but its certainly plausible.  Someone on here may know the facts.

@jamespa @johnr from my understanding COP is the ratio of how much heat energy a thermal machine can move compared to the work (electrical input) done. It is not efficiency as you cannot have more than 100% efficiency. Efficiency indicates losses in a system for example petrol is used in a car, when burnt 30% is motion energy the rest is heat energy.

There are two COP formulas, one for a thermal machine that moves heat from a hot store to a cold store (your humble fridge) which is defined as

Heat Generated / Energy In = COPcooling

and one for a thermal machine that moves heat from a cold store to a hot store (your heat pump) which is defined as

(Heat Generated + Energy In) / Energy In = COPheating

A lot of articles incorrectly define COP as efficiency which it is not.

Hope this helps to clarify things 🙂

@bontwoody thanks again for your input and the link to the OEM forum. I'm now running off the Samsung controller not the third party thermostat. It was very easy to do once I had the right info.  I've not been able to test anything else as Last night the Agile prices were negative post of the night so I left the heating on with the thermostat set at 23deg.  This morning we woke up to a very warm downstairs, the floor at 24° and we opened the front door for a while to cool down a little.  We haven't needed any more heat today.

Frustratingly the legionella cycle is set for the early hours of Sunday morning but the water isn't getting to 60° to finish the cycle so it runs the full 8 hours it is set for (the immersion heater isn't running that long according to the Octopus figures). The Samsung controller records the energy used as if the immersion heater is on for the full 8 hours so this screws the figures for Sunday. I'm going to do the same tonight, but with the thermostat   set lower, and see what the energy used and generated is like on a longer run time with the flow temperature around 30°

What I would like is to remove the secondary pump, remove the buffer tank or change it for a volumiser and change the primary pump to a PWM pump. I have to respond to the installers tomorrow and I will see what they will agree to do to get things set up well.

We've had 4 EV's siince 2017 and had an i3 for a weekend test drive.  It wasn't really big enough for us at the time but it was probably the most fun to drive, being so much lighter than most EV's must help. We still have the e-Golf, 85000 miles in it so far, and an ID3. I started with a Leaf as a cost experiment and loved the drive and costs so much we bought the Golf and would be very reluctant to go back.

Posted by: @technogeek

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A lot of articles incorrectly define COP as efficiency which it is not....  you cannot have more than 100% efficiency...

Hope this helps to clarify things

Completely agree that 'efficiency' is strictly incorrect terminology.  The efficiency (of a heat pump) would be (something like) heat out/theoretical maximum heat out (calculated presumably from the Carnot equation) given the energy in.  I think I saw somewhere that this is still only around 50%, but I didn't see the derivation so cant be certain its correct.

I admit to writing loosely (on this forum) that the 'efficiency' of a condensing boiler can be as high as 110%.  Of course this terminology isn't strictly correct either, the figure of 110% in this case is the ratio of heat out to declared calorific value of the fuel used.  This can be >100% because the declared calorific value (I am told) doesn't include the energy you can extract from the condensation process, which of course releases latent heat.

@johnnyb No problem, glad it helped. So what flow temperature were you using on the heating last night? UFH is known to have quite a bit of hysteresis and can easily overshoot.

With respect to legionella cycles, opinions differ greatly. Have  a look at this

you may not need to go as high as 60C. If the immersion is kicking in constantly then that may account for a low COP.

 The buffer tank can be converted to a volumiser with some jiggling of pipework and blanking plates. If you can get rid of the secondary pump then that would be a win. IMO getting a PWM pump would be a good idea.

Yes the i3 is certainly nimble. I shut up a mate about EVs ruining the roads because of their weight when I proved to him, his car was heavier than mine 🙂

Posted by: @bontwoody

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Yes the i3 is certainly nimble. I shut up a mate about EVs ruining the roads because of their weight when I proved to him, his car was heavier than mine 🙂

You've got the right EV for that.

I've emailed the installers today with a list of things I have changed, mentioned changing from 2 pumps to 1 PWM pump and asking about removing the buffer or changing it to a volumiser.  We have a double building plot and still have the second house that needs plumbing and heating so they should be trying hard to keep us happy, or they will be offended and walk away!

The flow temperature is around 30° with the floor getting to 23ish before the thermostat switches it off. I then left it off until about 2pm, when we were feeling cooler as the sun went in. It is on a setback from 4-7pm to avoid the Octopus Agile peak time. I will see a bit more what it does this evening.

I'm not concerned about the legionella cycle, I might even turn it off as we use lots of water and heat to 50 overnight, but I want to make sure it is working properly before it is all signed off.

@johnnyb It sounds like you have got a good handle on this now and the reasons why its not performing well are getting fewer and fewer. Some kind of monitoring would give you a better idea of whats working as you think. If Homely gives you that then it will be very useful. 🙂

@bontwoody From what I have read Homely gives limited monitoring to the end user but it does make things simple and is supposed to be making lots of adjustments all the time so the HP is running as efficiently as possible.  If it keeps the system running well and lets me know how well it is doing I will be happy 😀 

If TechnoGeeks's way of working out the COP is correct then the COP has been 4 today, which is probably good when it has been 2-5° outside.

@bontwoody Does your Samsung wired controller switch the heating off when it gets to the set temperature or does it go quite a bit over temperature, or do you just use the WC?  I've been trying to use the wired controller but it doesn't switch off the heating until it gets a lot over the set temperature. At the moment it is set at 19 and the temperature is at 19.8 and it is still running. I've been stopping it by either switching the heating off or turning the temperature down a degree or two until it switches off.

I can't just use the WC, even with the flow temperature around 25° the house is getting too hot and it needs to shut down for a while once or twice a day.