ASHP DHW monitoring tank temperature

[Far2wired]

After many years running a combi gas boiler we took the plunge and replaced with an LG R32 7kWh air source heat pump. The system has now been in for 3 weeks (today in fact). We reported an issue to the installer over a week ago that it seems we are running out of hot water quickly. Understanding this is no longer instant hot water and we are not going to be mixing with cold as much I did some measurements... Hoping someone can shed some light if this is an issue or we are expecting too much from the system as we have only ever owned gas combi boilers in the past.

 

Before someone showered I read off the controller the temperatures shown

DHW = 47

Water IN = 22

Water OUT = 22

(The DHW is set to 55C)

 

Shower is a digital Mira platinum set to 35C. We use the ECO setting and measured the flow with a jug and a stopwatch over 1 min = 6 ltrs of water outputted. Shower was ran for 20 mins, by which time the water was noticeably cooler, to the point it was not comfortable to shower.

 

Controller temperatures

DHW = 33

Water IN = 36

Water OUT = 43

 

The installers fitted a 210ltr unvented tank. This was sized based on our property - 3 bed. 

 

So this one shower used a total of 120 ltrs of water (some of that mixed with cold). For those that monitor the water temps do you see a drop like this or is our system not kicking in soon enough to maintain the heat in the tank?

 

[SteamyTea]

Sounds like something is amiss.

43 minutes ago, Far2wired said:

DHW = 47

Water IN = 22

Water OUT = 22

 

[dpmiller]

so the ASHP cuts OUT at 55c but what is it's cut IN point? It had started to reheat the tank by the time you were finished, but that's too late.

[Far2wired]

My mistake... Seems DHW is set to 50C and that is locked maximum.

 

Did another test with the DHW tank starting at 50C. Ran the shower and ASHP did not start until tank was down to 40C temperature. As you say that is too late as the water is being replaced with cold. After stopping the shower after 5 mins tank dropped to 30C pump now definitely on!

 

Is it possible the pump is operating on a 10C delta of DHW target and tank actual and is that configurable? I'd check the installer menu however I'm sadly locked out until I gain that level of trust the installer is looking for. For some reason they think customers will "fiddle" with the settings ?

 

[SuperJohnG]

You'd never maintain heat with an ASHP it just doesn't heat it fast enough. This is why you need more storage, 210l sounds too small to me as you store at a lower temp. 

 

You either need to store water at higher temp which means you'll lose the COP on the ASHP and it'll costs more or possibly a bigger tank. 

[Far2wired]

We have solar pv and thermal. Still waiting for installers to fit iBoost controller and plumb in the solar thermal. 

 

Problem seems to be the solar thermal is unvented, the existing tank will be discarded and the panel outputs attached to the second coil in the tank. However there is no control of maximum temperature. I have been told the ASHP has a max return temp, anything higher than 65C will cause damage, I cannot find anything in LGs specifications to confirm that. So the installers are planning on a heat dump for any excess.

 

Even if I could heat the tank to 65C still makes me think why they installed a 210L cylinder as on its own the system is not fit for purpose. I've seen the quoted recommended figures and our shower is efficient at 6 litres per minute (some are over 10 lpm).

 

[dpmiller]

there's probably an installer setting for max temp, likewise for the cut-in point.

[ProDave]

19 hours ago, Far2wired said:

Before someone showered I read off the controller the temperatures shown

DHW = 47

Water IN = 22

Water OUT = 22

(The DHW is set to 55C)

That shows the tank temperature was 47 degrees and flow and return from the HP both 22, so the HP was probably idle.

 

 

19 hours ago, Far2wired said:

Shower was ran for 20 mins, by which time the water was noticeably cooler, to the point it was not comfortable to shower.

 

Controller temperatures

DHW = 33

Water IN = 36

Water OUT = 43

Tank temperature had dropped to 33 degrees, water flow temperature out from the HP is now 43 degrees and water return temperature to the HP is 36 degrees (so delta T 7 degrees) The heat pump has turned on and is busy re heating the tank.

 

There is a setting somewhere for DHW hysteresis, which is how much the hot water has to fall from your set point of 55 degrees before the HP turns on to re heat it.  you might need to adjust that.

 

20 minutes showering at 6L per minute was 120 litres of water.  What size tank?  It would have to be a small tank to run out of hot water jst from that shower.

 

Can you post a good picture of the hot water tank and give us details of it's size etc?

 

Where is the hot water probe?  you will see a thin wire going into a thermostat pocket somewhere on the tank.  This needs to be as low as possible, if there is more than one thermostat pocket, make sure it is in the lowest one.  When I first fired mine up I had the probe in the higher pocket, which meant you tank would be half empty before the HP even knew it was starting to run out of hot water, effectively halving the capacity of the cylinder.

[Far2wired]

Yes, first temps HP was idle. That was just to show what temp the tank was at before showering.

 

Just to confirm our DHW is set to 50C not 55C. Tank size is 210L. But with the shower at 36C I would expect some cold mixing with the tank starting at 47C.  

 

We have a Kingspan HPS210ERP. Thermometer is in dry stat pocket (G2), there is a lower stat pocket (G1) but I think that will be needed when solar thermal is plumbed in. Every cloud - at least its not been wired into G3 eh!

 

I have found a monitoring solution based on the Adruino platform (https://openenergymonitor.org/) but as I understand it would need a thermal energy meter (something like a Sharky 775 - which isn't cheap!). Has anyone got a similar setup where they are monitoring water temps?  I'm thinking whoever is the lucky person that connects up our thermal to this system will need to fit something similar to stop the temps getting too high.

 

 

 

[ProDave]

I am not convinced that is the best cylinder for you.  Look how high up the heat pump input coil is.  You have a 210L tank but it has a "dedicated solar volume" of 60L so when heated by the heat pump, you are only going to get 150 litres of hot water.  It is less surprising that you ran out of hot water when you realise that.  It is quite possible with the temperature probe location that there could only be 100L of hot water left before the heat pump even knew about it.

 

Moving the heat pump temperature probe to the lower pocket would not work, because the heat pump would never heat that bottom part of the tank so would never be satisfied.

 

The solar thermal system usually comes with a self contained controller that monitors pipe and cylinder temperatures.

[SteamyTea]

2 hours ago, Far2wired said:

Has anyone got a similar setup where they are monitoring water temps

I made one for a Solar Thermal system.

Was a bit crude, just a 'relay as a switch' to sense when the pump was on and a couple of 1Wire temperature probes to sense the temperature differences.

Then an assumption about the flow rate.

Was wired into a Raspberry Pi ZeroW.

 

It worked.

[Far2wired]

On 09/06/2021 at 13:16, ProDave said:

I am not convinced that is the best cylinder for you.  Look how high up the heat pump input coil is.  You have a 210L tank but it has a "dedicated solar volume" of 60L so when heated by the heat pump, you are only going to get 150 litres of hot water.

 

Now that does makes sense. The solar thermal has not been connected yet or our iBoost controller. Once the solar thermal is plumbed in that would be the primary source of heat with the HP topping it up. In the winter our solar thermal on average would heat water to 30C. I'm assuming the max temp the tank would get to is set to 65C so we would be mixing more cold water.

 

I guess we will have to see once these last bits are fitted and see but during winter will be the test...

 

[Nickfromwales]

On 09/06/2021 at 07:35, Far2wired said:

So the installers are planning on a heat dump for any excess.

Eh?!?

If the cylinder stat is set to shut off at 50oC then the HP will shut down and the circulation pump will not operate ergo water that hot can never get to the HP. Any temp above 50 will just stave off the HP from coming on, and that’s all you need. 
If I was designing this I would fit a second 2-port zone valve in the return pipe exiting the UVC to arrest convection circulation, eg so the HP does not / cannot become an accidental radiator. Putting a heat loss aka dump circuit into this arrangement is just crazy. Any of that heat energy should be seen as useful and harvested in the UVC. 210L @50oC is mediocre, but 210L at 75-80oc is a lot of useful DHW. Any uplift in temp = more stored heat energy which absolutely should not be dumped away. 
What is the control methodology for the ST? Is it supposed to have a dump circuit and for that to be on a high limit stat on the upper 1/3 of the UVC ( 3rd party not HP or UVC controls ). 

[Far2wired]

Apologies for not replying sooner, this install has turned into a nightmare... Absolutely, I don't understand why the installers think they have to dump the excess. I'm getting increasingly frustrated with the installers as it will be 6 weeks this Tuesday since the HP was fitted and they have still not arranged for the ST engineer to attach it up. At this time as the ST coil is at the bottom of the tank (as you can see above) we only have 60ltrs of usable hot water. We were pressured into paying the invoice to fit the HP being told the RHI scheme payments could go down if we delay. We have left messages every day on the installers phone for when this is going to be finished and it seems to roll on and on with no firm completion, when we do get  through we are promised a phone back which never happens. Really worried now this will never get done. Does anyone have any advice how we can resolve this as it seems the company has no interest in completing this job?

 

Re the ST setup, (I have a basic understanding but in no way capable of modifying the setup myself!). The roof module are tubes, the controller is a Resol DeltaSol BS, before it was turned off was heating a vented tank.

 

[SteamyTea]

59 minutes ago, Far2wired said:

Does anyone have any advice how we can resolve this as it seems the company has no interest in completing this job

Just find your own competent plumber, it is not a difficult thing to do, unless you have some non-compliant components i.e. soldered joints on ST system.

Or dump the ST, replumb the store so that the HP heats via the lower coil, then fit PV.  Sell the ST on eBay.

You may loose money, but you will have a better system.

 

Consider a claim against the original installer.

Edited June 27, 2021 by SteamyTea

[Scoobyrex]

Did you pay by credit card ? If so start a claim back.  The process starting will kick them into gear.