New to the world of ASHP!

[SteamyTea]

1 hour ago, Marvin said:

My 1400mm high tank can go from 25C at the bottom to 60C at the top. 

Bottom of my tank usually settles around 10°C higher than the temperature of the incoming water.

It is worth, when looking at my chart, that most mornings I have a bath full out of it after the E7 heating window has finished.

[MYLOUBYLOU]

This is what the boost circulation is connected to. Pump I’m guessing?!

[MYLOUBYLOU]

Our weather compensation curve

[Dave Jones]

mains gas an option ?

[MYLOUBYLOU]

19 hours ago, Dave Jones said:

mains gas an option ?

No gas in the village. Average is 500kwh a month. Dhw seems to be main driver for consumption. Thought about solar thermal panels but doesn’t seem to be cost effective & doesn’t provide much in winter. Hoping levies will be reduced on electricity over the next decade

 

19 hours ago, Dave Jones said:

[Mike-P]

We had an ASHP installed a few weeks ago and are still working out how to get the best operation. We went through a period when it was tricky to get hot water and it turned out to be a number of things.

1. Our system is installed in an S plan rather than the standard Y plan. In other words, it can be run as a standard boiler that allows space heating and DHW heating to be on at the same time. The ASHP is only configured to 'space heating' and had weather compensation on. This resulted in us trying to heat the DHW with the heat pump running at 37 degrees.
2. The pump and valve circulating the water round the coil in the cylinder are on as soon as the water heating is turned on, however, the heat pump might be pushing cold water for 5 or 10mins if starting from cold. During this time our ASHP is cooling the water in the cylinder rather than warming it.
3. If we are running both heating and DHW heating from cold it takes much longer to start pushing water that is hot enough to warm the cylinder, extending point 2 above.
4. We had an immersion that was set to do a legionella cycle once a week by turning on the ASHP (not an immersion) but that was pushing weather compensated 37 degree water through the cylinder, in an effort to get water to >60degrees it was taking our previously hot cylinder and cooling it down to about 35.

In our system we have the heat pump just circulating the R32 into a plate heat exchanger and back. The cylinder coil and UFH closed systems are heated by that heat exchanger. The cylinder is 200l with large coil. The rooms are controlled using heatmiser stats like yours. There are 4 adults in the house, a 3 bedroom that is powered by a 10kW Midea ASHP.

Currently we are getting water at about 46degrees by doing the following (solving the corresponding issues above);

1. Turned off the weather compensation mode and set it to a programmed temperature. 40 degrees when we have the space heating programmed and 50 degrees when the DHW heating is programmed to be on.
2. we have the DHW heating set to periods that directly follows the space heating times. I plan to add a clip on temp switch to the R32 loop to make sure that the circulating pump for the heating and DHW only runs when the R32 is > eg 35degrees.
3. when we run the ASHP at 50 degrees we have the room stats programmed to be a couple of degrees lower having the effect of shutting off the heating and pushing all of the hotter water through the cylinder coil.
4. the legionella cycle is deactivated.

I had gone into the detail here in case some of this is relevant to your situation.

Factors I've been trying to consider include efficiency of timing the water heating, might be a mistake, but trying not to heat the water overnight or early morning when the outdoor temp is coolest, also running the heating and the DHW heating for a period to get the cylinder up to 40s then blasting (!) it with 50 degrees to give it a final top up of heat.

I'd like to set it so that the valve for the cylinder only opens if the water in the R32 loop is warmer than the cylinder but not sure how to do that without bashing out a Raspberry Pi controller (I'd be grateful for some advice on that one if there is a simple way without me writing some Python and hacking together a load of electronics). Alternative would be to dig up the concrete again to connect the cylinder sensor to the outdoor unit and run it on a Y plan but I think the current S Plan gives more flexibility and potential for efficieny.

Some things I noticed with your system;

• you appear to have 5 pumps!
• your boost timer seems to be connected to a pump rather than the immersion. I haven no idea why you might do that.
• It looks like you have an Ecodan pre-plumbed cylinder with active heating. I don't think it uses a coil unless you have the solar version. It actually pumps the water out of the cylinder, through a plate heat exchanger and back into the cylinder again. Mitsubishi recon this heats the cylinder quicker, and maybe they are right. So the stuff on the bottom right of your cylinder in the picture is the pump, scale trap and heat exchanger. If your cylinder is hotter than your heat pump is running then it will for sure cool your water down very quickly. Also note: if the cylinder pump comes on when the heat pump is not on for some reason it will have the same effect of cooling down your hot water rather rapidly.
• Our ASHP only comes on when a heatmiser stat calls for heat or water heating. Yours coming on and off without a call seems weird. Are you using the wireless neo air stats? they have a 'safety' mode that turns the boiler on (I think from memory for 7 mins per hour) if the signal from a stat is lost (including a flat battery). If you are using those wireless ones you can turn off the 'safety' feature at the wireless controller. 
• (given that it is pre-plumbed and designed to be used with your heat pump and the big box of electronics on your cylinder it seems odd that you would be having those problems unless sonething has been configured incorrectly.)

I'd be inclined to periodically check the pump below the TF1 to see if it is coming on when the heat pump is either off or running cold. That would quickly chill your hot water!

Edited November 25, 2021 by Mike-P
correction

[ProDave]

One thing from the above post.  DO NOT try and run heating and hot water at the same time with an ASHP.  Most have different flow temperatures for each and most let you set whether hot water or heating has priority (i.e. which one operates if both are demanded at the same time)

[joth]

On 11/11/2021 at 19:57, MYLOUBYLOU said:

Our weather compensation curve

 

Hmm 50°C seems a very high target temperature for a system based on UFH. When the outside temperature is below 5 it's going to give a very poor COP. 

Personally I set the curve to 30°C max rolling down to 25.

Mine is controlling an electronic thermostatic mixing valve so actually setting the temperature running in the loops, and no buffer tank. So I need the max flow temp low to protect the wood floor finishes. If your system has a buffer tank and a separate manual fixed setpoint TMV then I guess the compensation curve serves a completely different purpose.

 

(I'd really feel for the ASHP engineers in 10 time trying to understand all the different system designs people end up with, no two installs are ever quite alike.)

Edited November 25, 2021 by joth

[SteamyTea]

2 hours ago, joth said:

(I'd really feel for the ASHP engineers in 10 time trying to understand all the different system designs people end up with, no two installs are ever quite alike.)

That is a very valid point.

[rh2205]

We are in the same boat, no idea what even is efficient? How much kWh should you expect to use in a day, we thought our system wasn’t too bad but it’s cold today & now it’s drinking the electric ?. 15kwh today so far it’s heated the water once for 1.5hrs & been on for 4hrs so far set to 19.5C. It’s a 220sqm refurbished place. Since install at end of may we’ve used 415kwh.

[Mr Punter]

17 minutes ago, rh2205 said:

It’s a 220sqm refurbished place. Since install at end of may we’ve used 415kwh.

 

Are you sure you did not miss a zero from the end?

[rh2205]

Hmm no, though you are doubting me because also we have this weird thing on the immersion heater which states we’ve only use 1.14 kwh since may. @Mr Punter would love to know whether I just don’t know how to read a meter or it’s broke!

Edited November 25, 2021 by rh2205

[SteamyTea]

26 minutes ago, rh2205 said:

Since install at end of may we’ve used 415kwh.

 

7 minutes ago, Mr Punter said:

 

Are you sure you did not miss a zero from the end?

If it is a HP that is heating the water, then that will be 3 to 4 times larger, with only a small proportion of it going to space heating.

[rh2205]

It’s a heat pump yes no gas in the village! Now I’m freaking out about whether these meters are busted!

[Mr Punter]

3 minutes ago, rh2205 said:

Hmm no, though you are doubting me because also we have this weird thing on the immersion heater which states we’ve only use 1.14 kwh since may. @Mr Punter would love to know whether I just don’t know how to read a meter or it’s broke!

 

 

Well that is a kick in the bollocks to any ASHP deniers!

[rh2205]

We only have radiators on a crappy big loop spanning a 16m wide house & no manifolds so I really don’t think this is the epitome of good efficient design either! But in all honesty I would really appreciate whether these meters can actually be wrong because I don’t think we have a magical house. It’s refurbished by a bog standard builder after all and there’s a lot of details I knew where bad haha.

Edited November 25, 2021 by rh2205

[SteamyTea]

1 minute ago, Mr Punter said:

 

 

Well that is a kick in the bollocks to any ASHP deniers!

well it does depend on how sweaty they are, and for how long they are kept like that.

[SteamyTea]

3 minutes ago, rh2205 said:

We only have radiators on a crappy big loop spanning a 16m wide house & no manifolds so I really don’t think this is the epitome of good efficient design either!

Depends on what the overall heat losses are, and the peak load is.

Have you had a heat loss calculation done?

Edited November 25, 2021 by SteamyTea

[rh2205]

I have an EPC… the installer did some calcs on special software never saw theM other than it states design was on sheet for 7.49kwh heat loss.

[SteamyTea]

1 minute ago, rh2205 said:

I have an EPC… the installer did some calcs on special software never saw theM other than it states design was on sheet for 7.49kwh heat loss.

What is the EPC Score, and I suspect you mean the maximum heat load is 7.49 kW.

What size is your ASHP?

[Mr Punter]

For 6 months, that just seems very little.  We are on gas and have averaged 30kWh per day, plus 17kWh per day for electric.

[SteamyTea]

Just now, Mr Punter said:

For 6 months, that just seems very little.  We are on gas and have averaged 30kWh per day, plus 17kWh per day for electric.

If you take away 2 kWh a day for cooking, and assume a CoP of 3.5 if an ASHP was installed, and the gas boiler has a true efficiency of 85%.

 

True gas usage for water heating:

 

28 [kWh.day^-1] x 0.85 [eff] = 24 kWh.day^-1

 

Now a 3.5 CoP ASHP:

 

24 [kWh.day^-1] / 3.5 [CoP] =  7 kWh.day^-1

 

Half a year is 182 days.

 

182 [days] x 7 kWh.day^-1 = 1724 kWh

 

So something does seem amiss.

 

2, 5 minute showers, at 10 lt.min^-1.day^-1 would be around 3 kWh.day^-1, or 540 kWh, which seems plausible.  If that was heated at CoP of 3.5, then 154 kWh over 6 months, which is a third of the meter reading.

 

[rh2205]

So full disclosure we only have 1 small bath a day for a child & maybe 2/3 showers a week. I use the gym a lot. It’s a 13kw heat pump in middle-south ish England.

Edited November 25, 2021 by rh2205

[rh2205]

So what about the weird immersion reading. This is also since may obviously only comes on once a week or so I was told.

[SteamyTea]

1 minute ago, rh2205 said:

So full disclosure we only have 1 small bath a day for a child & maybe 2/3 showers a week. I use the gym a lot. It’s a 13kw heat pump in middle-south ish England.

Then that 415 kWh seems plausible, especially as the ASHP, at 13 kW (not kw) is well sized to supply that.

For a laugh, try and take daily readings, and if you can get the outside and inside temperatures as well, all the better.