Heat Pumps: anyone have one/thought about it?

[b0rn2sk8]

Yes, my tank has 3 modes.

Schedule - the tank heats once to the desired temperature per scheduled block. You can set multiple blocks per day but it will only heat it once in that block (e.g. 0300-0500). You can also schedule two different temperatures if you want, I don’t bother.

Schedule plus reheat. As above but you also have two additional settings ‘reheat temperature’ and ‘hysteresis’. The tank will heat once in that block as above, when the temperature drops by your hysteresis (difference between actual and set temperatures) the tank will then reheat automatically to your re-heat set point which can be lower than the main heating cycle to save energy. It’s designed to be a little too up.

So say your standard set point is 50C, the re-heat is 45C and your hysteresis is 10C. The heat pump will heat it to 50C once in that block. If the temperature drops by more than 10C it will reheat the tank to 45C. It will keep reheating it each time it drops below 40C until the next scheduled heating cycle.

Powerful - it’s selectable mode that immediately boosts the hot water with maximum output (heat pump plus 3kw immersion) to the set temperature.

I’ve never used powerful and I’ve tuned off reheat as we seldom run out. I just heat it once per day during the cheap period.

With reheat you have to remember the temperature probe is in the middle of the tank, not the top. Due to stratification, the top of the tank is much hotter.

I’ve had a shower with the tank showing 32C and it was perfectly warm, although it was cooling off towards the end. It was showing 24c when I got out.

You’ll not be able to pull hot water continuously but in reality people have a shower, spend 10 mins getting dry etc and in that time, if the tank is in reheat mode and it’s dropped below the threshold to reheat, it will have kicked on and replenished a lot of the consumed water in that time.

 

[dirtychinchilla]

Daikin specific.

Increased WDC from 33C @ -5C to 36C @ -5C.
While monitoring the LWT didn't go above 34C even with modulation enabled so I will set it to 35C and wait for a properly cold day to check again.
Steady state 19C saw 500-800W at 1C OAT
Changed Delta-T from 4C to 3C to see the affect on flow rate (7 l/m).
Steady state 19C dropped to 400-600W at 1C OAT
Flow rate stayed at 7 l/m (25% PWM).
Derestricted pump from installer menu.
Flow rate stayed at 7 l/m so 25% PWM appears to be a hard limit on my 4KW Daikin.
I will set the pump back to restricted again to be safe.

Any reason why you're compressing your dT? A higher dT typically leads to higher efficiency through more efficient heat transfer, plus pumping energy reduces with reduced flow rates, which is an effect of higher dTs.

 

[b0rn2sk8]

Daikin requires a minimum of 7l/min so the dT on the inlet and outlet is what it is at these low power levels.

Edit: it’s 6C outside, 21C inside, 32lwt, 28 return, 7l/min, 350w.

That’s about as low as it will go, dare I say it, my mere 6kw* heat pump is a bit oversized.

*thr 4kw, 6kw and 8kw Daikin Athena 3’s are identical bar software.

 

[reef]

Mines running quite a bit higher than the weather curve today for some reason. Its 6C outside, which should be about 35C leaving water temp, but instead its sat at 38C. Im not sure why its doing this, as its on pure weather compensation, so modulation shouldn't be a factor.

Its heated the house up to 22.6C as a result. Its so difficult to get it right as it has a mind of its own!

 

[bimbleuk]

Mines running quite a bit higher than the weather curve today for some reason. Its 6C outside, which should be about 35C leaving water temp, but instead its sat at 38C. Im not sure why its doing this, as its on pure weather compensation, so modulation shouldn't be a factor.

Its heated the house up to 22.6C as a result. Its so difficult to get it right as it has a mind of its own!

I'm trying to reduce the Space Heating/Overshoot setting from 4 to 2 now 1. Supposed to stop the LWT rising too much as the temp approaches the set point so not much use in LWT mode.

My house was over 20C with a set point at 19C. I raised my WDC to try heat the room faster and then trigger a faster turn off but it's being stubborn. So now lowering the WDC again with the lower overshoot setting. If it repeats the .5C overshoot again I may be getting somewhere.

 

[bimbleuk]

Any reason why you're compressing your dT? A higher dT typically leads to higher efficiency through more efficient heat transfer, plus pumping energy reduces with reduced flow rates, which is an effect of higher dTs.

I was mainly seeing if I could influence the flow rate as it always seemed to stay the same regardless of emitter such as Fan Coil 4DT or Rads 10DT. I was constantly hitting the same minimum flow rate as the bigger units.

I then found a surging issue in fan coil setting just before a cycle off which left the pump stuck at 25 l/m which I can clearly hear. So rads with DT 10 is my only setting anyway. I don't have problems with short cycling or many defrosts so just playing with the WDC to balance the power draw, heat up and overshoot. Overshoot seems to bug many Daikin heat pump owners.

 

[SkyTerran]

Does anyone have a combination of radiators and UFH working with a heat pump? How are they connected in terms of water pipes?

I have a single water circuit that goes radiators -> UFH -> radiators, which may be a problem.

 

[b0rn2sk8]

That makes you think it will be a problem?

I would have thought it would be all plumed in parallel (assuming it’s been done correctly).

 

[Simon D]

Does anyone have a combination of radiators and UFH working with a heat pump? How are they connected in terms of water pipes?

I have a single water circuit that goes radiators -> UFH -> radiators, which may be a problem.

Yes.

I have UFH downstairs 15mm pipework that is divided into 10 zones and 8 radiators upstairs 10mm pipework which splits from a main flow manifold into the two separate circuits.

Octopus wanted to installed my heat pump as a single loop for the UFH and radiators, move the thermostat to the hallway, disconnected all the UFH controls, but I ask them to leave all the controller in place just in case If I had any problems.

I found that the 6 rooms downstairs were getting far to hot almost tropical temperatures this was due to how the builder separated UFH into zones and not the same size.

I asked them to reconnect the UFH controllers and moved the Daikin thermostat to the main bedroom as this was the original location when I had my gas boiler.

Downstairs room are now 21-22C and upstairs bedrooms 19-20C. The only real issue I have is the overshoot of the Daikin thermostat by 1C

Is your UFH on just a single zone?

How do you control the room temps on the UFH .

 

[bimbleuk]

Downstairs room are now 21-22C and upstairs bedrooms 19-20C. The only real issue I have is the overshoot of the Daikin thermostat by 1C

Seems Daikin have a 1-1.5C overshoot whatever you do. I tried all the settings and moved my WDC up and down. Best I can do is delay the overshoot for 3-4 hours.

I tested it by rebooting the controller with a setpoint of 19C and a room temp of 19.5C. The Daikin still wanted to restart and reach the 1C overshoot before stopping.

 

[b0rn2sk8]

Correct, it’s 1.5C above and 0.5 below the stet point temp, it’s to help increase run times and reduce cycling, particularly in houses with higher heat losses (e.g. old and Victorian) and/or low thermal mass (e.g. new build) which can swing quickly.

All you can do is set a lower set point when it’s mild. It will be a bigger issue of your heat pump is oversized and can’t modulate low enough when it’s milder.

 

[Simon D]

Seems Daikin have a 1-1.5C overshoot whatever you do. I tried all the settings and moved my WDC up and down. Best I can do is delay the overshoot for 3-4 hours.

I tested it by rebooting the controller with a setpoint of 19C and a room temp of 19.5C. The Daikin still wanted to restart and reach the 1C overshoot before stopping.

I tried the same to fix the overshoot when reheating with no luck

I lower the LED brightness on the Daikin room thermostat that fixed the wrong temperature that I was seeing compared to my room thermometer. (I was seeing about 1 degree), thinking that this was the problem.

My system running with a 2 point curve WDC:
45 @ -3
30 @ 19
Modulation:2
Emitter type: Radiators

I have all the UHF controls set to close down at 22C and Daikin room thermostat set to 19C for upstairs radiators which overshoots to 20C in the evening when reheating.

 

[b0rn2sk8]

The LEDs won’t fix overshoot, that’s more about it reading the wrong temperature (too high) because it generates its own heat.

You can’t ‘fix’ the overshoot, it’s hard coded. You can’t account for it by setting a slightly lower target temperature but that also means it will not kick on until it’s colder if it cycles off.

edit: it’s worth mentioning all heating system do this to an extent because it reduces boiler or heat pump starts ups which use lots of fuel and reduce efficiency.

 

[bimbleuk]

Correct, it’s 1.5C above and 0.5 below the stet point temp, it’s to help increase run times and reduce cycling, particularly in houses with higher heat losses (e.g. old and Victorian) and/or low thermal mass (e.g. new build) which can swing quickly.

All you can do is set a lower set point when it’s mild. It will be a bigger issue of your heat pump is oversized and can’t modulate low enough when it’s milder.

Ideally needs a setting to roughly match the heat loss expectation. Yeah at 12C outside my WDC cuts off the heating.

Weirdly I have the opposite of short cycling in that my heat pump will turn of for 3+ hours just to loose the overshoot. The system cools down quite a lot on cold days and then goes flat out to catch up (Quiet mode caps this by ~20%). What I found helped was to artificially stop the heat pump via the scheduling before the overshoot gets too high.

 

[SkyTerran]

I got a couple of quotes and I've been trying to better understand what the installers want to do.

I have UFH with the following spec:

Pump Pack	NovaTherm™ Heat Pump Circulation Pack (UPM3 H4 Auto)
Flow Temp / Pressure	35–40°C

No mixing valve is installed.

Octopus are telling me they don't plan to install a mixing valve. The maximum design flow temperature in their quote is 50C (which is way above the 40C that the UFH is designed to handle). Do you think I should ask them to install a mixing valve anyway?

According the other quote 38C are enough to compensate for the heat loss of the house. I think Octopus always put 50C on their Eco quotes.

Also do you think I should ask them to remove the already installed pump?

The heat pump Octopus are quoting is Daikin Altherma 3 6kW.

 

[dirtychinchilla]

I got a couple of quotes and I've been trying to better understand what the installers want to do.

I have UFH with the following spec:

Pump Pack	NovaTherm™ Heat Pump Circulation Pack (UPM3 H4 Auto)
Flow Temp / Pressure	35–40°C

No mixing valve is installed.

Octopus are telling me they don't plan to install a mixing valve. The maximum design flow temperature in their quote is 50C (which is way above the 40C that the UFH is designed to handle). Do you think I should ask them to install a mixing valve anyway?

According the other quote 38C are enough to compensate for the heat loss of the house. I think Octopus always put 50C on their Eco quotes.

Also do you think I should ask them to remove the already installed pump?

The heat pump Octopus are quoting is Daikin Altherma 3 6kW.

What do you want to do with the higher flow temp?

 

[SkyTerran]

It's a mix - radiators on the 1st floor and UFH on the ground.

 

[dirtychinchilla]

It's a mix - radiators on the 1st floor and UFH on the ground.

Are you anticipating changing the radiators? If so, they'll be sized for a lower flow temp - not 50

 

[SkyTerran]

No, no radiator changes - the current are big aluminum radiators.

I guess a problem may be if say the software on the heat pump resets (or it looses it's settings for another reason) and it starts pumping 60C water through the UFH, without a mixing valve.

 

[b0rn2sk8]

I think you’re overthinking it. Even at default settings, the heat pump isn’t going to be set that high and I think you’d notice the outside unit at full tilt for the hours it would take to get the surface temperature up to that kind of level (it’s not the flow temperature that’s the issue for UFH, it’s the surface temperature of the floor covering).

Not to mention the fact you’d be cooking in the house long before that and the thermostat would cut the heat pump off.