ASHP buffer

[JohnMo]

Currently we have a house UFH and summer house UFH operating as a single zone. But the summer house heating is pretty rubbish, so use an electric heater also.  Now the temps are dropping the electric heater is starting to run through electric.

 

to heat the summer house twice over the last couple of days and used around 14kWh. It is only going to get worse as temperature drop, becuase the the summer house is being used most days.

 

So issues are, I need two very different flow temperatures, one for summer house and a much lower one for the house, the heating season for the summer house is much longer also. So need to make two zones.

 

Since decommissioning the gas boiler, I have an Alpha Flowsmart 50L cylinder (previously used for combi boiler preheating), so will repurpose as a buffer, plumbed as a parallel, 2 port configuration across the supply and returns. Will follow the recommendation of Kensa heat pumps complete with PRV (by-pass valve) to engage the buffer only when needed.

 

 

 

Also in my parts store is an ESBE CUA100 (cheap off eBay a while ago). This is an electronic mixer valve, that can be operated in either of two modes, fixed flow temperature or a modulating flow temperature based on house temperature. It incorporates a timer which works in both modes and allows a second temperature to be set. So in theory you can increase the temperature (either house temperature or flow temp) during E7 and lower at other times. So will install this and a pump on the house UFH. The summer house will be run on weather compensation, direct from the ASHP.

 

CUA100_en_F_LR.pdf

 

Just waiting for a new mixer valve to arrive. Controller is installed and everything seems to work, as it should. Have put the controller in the lounge using now defunct thermostat wiring and will use this room as a reference temperature. Will run on house temp mode first to see how it goes. If it not stable, its just a setting change to switch mode.

[sharpener]

Quite cunning but the drawback to all schemes involving mixing valves is that the HP has to run at the higher of the two temps, so you get the lower of the two possible CoPs all the time.

 

Is there any possibility of a bit of time division multiplexing so you can run each zone on its own at the optimum flow temp, for part of the time at least?

 

Similarly, I am about to re-do my (current, gas-fired) HW programming so it heats up while the CH is off and hence doesn't compromise the weather comp and the attendant condensing mode operation.

 

 

Edited November 29, 2023 by sharpener

[Conor]

Why not try increasing the flow temp by 5c, reduce the flow rate to the main house and increasing it (if possible) to the summer house?

[JohnMo]

6 hours ago, sharpener said:

Quite cunning but the drawback to all schemes involving mixing valves is that the HP has to run at the higher of the two temps, so you get the lower of the two possible CoPs all the time.

 

Is there any possibility of a bit of time division multiplexing so you can run each zone on its own at the optimum flow temp, for part of the time at least?

 

Similarly, I am about to re-do my (current, gas-fired) HW programming so it heats up while the CH is off and hence doesn't compromise the weather comp and the attendant condensing mode operation.

 

 

The good thing with this mixer is there is not always mixing as with a normal UFH mixer.  So I could inject the full heat to the house floor for a shorter period. 30 to 32 I heat the house in 7 to 8 hrs for the whole day. So I may be able to heat house enough in a shorter period. I am hoping the controller runs as hot as possible, then when it starts to see house temps increase starts to back off flow temperature.

 

My main issue is the kWh used in the garden room is averaging around 7kWh, by direct electric. At my current flow temps the UFH in the garden room supports the room to 10 degs inside.  If I increase flow temp 5 deg, at full heat pump output the additional electricity load is around 200W at most temperatures. So instead of running a 2.5kW heater I drip feed the UFH but at suitable flow temp.

 

I am hoping the CoP hit is made up by running the UFH in the house for less time as it's the biggest user.

 

To make the heat pump output different flow temperatures, is a manual change of set point, so not practical on a day to day basis.

 

1 hour ago, Conor said:

Why not try increasing the flow temp by 5c, reduce the flow rate to the main house and increasing it (if possible) to the summer house?

I tried that a few months ago, trouble was even with the flow rates turned well down the house overheated and that was only at about 2.5 deg increased flow rate. There are only 2x 50m loops in the garden room and that cannot be run without a buffer, on its own. If I control the house to switch off without a buffer the heat pump just trips on low flow.

[RobLe]

Add insulation to the garden room ?  Add a fan boosted radiator ?

Zoning and time division multiplexing will reduce the amount of time the HP is heating the garden room and the house - so they would both need higher flow temps while they are on, and the HP get a worse COP for both cases.

[JohnMo]

6 minutes ago, RobLe said:

Add insulation to the garden room ?  Add a fan boosted radiator ?

Zoning and time division multiplexing will reduce the amount of time the HP is heating the garden room and the house - so they would both need higher flow temps while they are on, and the HP get a worse COP for both cases.

Lots of insulation already, floor and roof around 200mm, walls 140mm. 

 

Wall space is quite limited, so fan assist radiator not really an option.

 

Idea is to heat both during cheap rate, but only top up the garden room as required during the day. There will also be a month at either end of the heating season where the house doesn't need heating, but the garden room does.

[Conor]

30 minutes ago, JohnMo said:

Lots of insulation already, floor and roof around 200mm, walls 140mm. 

 

Wall space is quite limited, so fan assist radiator not really an option.

 

Idea is to heat both during cheap rate, but only top up the garden room as required during the day. There will also be a month at either end of the heating season where the house doesn't need heating, but the garden room does.

Storage radiator? At least it's direct electric heat during the day but charged up on cheap rate.

[sharpener]

1 hour ago, JohnMo said:

Wall space is quite limited, so fan assist radiator not really an option.

 

Nor a storage heater I imagine.

[ProDave]

Air to Air heat pump for the summer house independant of the main house.

[saveasteading]

4 minutes ago, ProDave said:

Air to Air heat pump

Everything else is 1 for 1 energy.

If you don't need cooling (and it should be avoided) then make sure the unit is primarily designed for heating efficiency.

[JohnMo]

My outlay for the mods will be quite small, main ones are antifreeze (10L) and an ESBE 3 way mixing valve and a new thermostat for the garden room; as I broke the previous one. Plus a few fittings I don't have.

 

Although I will take a CoP hit, not sure the cost for A2A would ever stack up. Plus not a fan of blown hot air.

[JohnMo]

27 minutes ago, saveasteading said:

Everything else is 1 for 1 energy.

Except the A2W I plan using (UFH already in and working, just not hot enough). Looks like I will take a CoP hit of around 0.4, but if the run time of the house heating comes down due to higher flow temps then maybe no hit in running costs (that would be a good upside if it happens)

[JohnMo]

Down to -7 for the next three days, so unlikely I will not be progressing much.

[JohnMo]

That's all the electric stuff done. The thermostats (2x) installed and working, the ESBE controller, mixing valve and actuator have all been hooked up and working during a dry test. Pump control is via the mixer valve microswitch, when mixing valve is closed i.e. no heat required, pump switches off. The closed mixing valve is a tight shutoff so will function as zone valve also.

 

Buffer filled with 20% antifreeze mix. It will have the by-pass valve installed and will be installed on the garden room side of a 2 port actuated zone valve. So only engaged with with a garden room heating only.

 

ESBE controller will manage the house flow temperature based on house temperature, you can set two temperatures and time them. You can limit the max flow temp so as not to damage anything.  Using the controller dry, if the target temperature is higher than actual temp, over a 10 minute period the the mixer fully opens the hot flow and closes the recycle flow.

 

Am using the house and or summer house thermostat, so either can switch on the heat pump, both are required to have no heat demand to switch off the heat pump.

[JohnMo]

So everything install a few days ago. With mixed results, couldn't get the garden room UFH to provide enough heat, to heat the room, above 12 degs. So have decided to use the floor heat to limit downwards heat loss, it will act passively not call for heat or switch it off, if on.

 

House UFH with ESBE electronic mixer is great. Basically decided to run in set temperature mode, so it controls flow temp. It allows two flow temperature to be set (T and T2) T2 is activated by external timer. T2 temp is run during E7 period. The mixer remains fully open with zero mixing of returns until it sees the flow temp, above set point and then it starts to move to allow more and more mixing until it maintains a fixed target flow temp.

 

This allows me to run a maintenance flow during the day below the WC curve and by setting the T2 target above any normal flow temp, I can charge the floor based on WC curve without interference of the mixer during the night.

 

The buffer with this setup is required, as the mixer almost fully closes off the hot water inlet when controlling flow temp in the day.

Repurposed 50L pre heat cylinder. Pipe with red handle water is added to top of cylinder, the other pipe behind water withdrawn at bottom of cylinder.

 

Circulation pump downstream of ESBE mixer. Pump mounted on IVAR manifold adapter, with temperature gauge and isolation valve. Insulation prior to pump has controller temp probe.

[JohnMo]

As an experiment I installed 2 Salus auto balancing actuators, one for each loop, on the garden room manifold. Reset the WC curve with a start flow temp of 34 (normally 29.6 deg). And it started to heat the floor, so left to run overnight, the summer house settles at 14.7 degs with an outside temp of 5 degs. A result - No need to have electric heater on all the time.

 

The Salus actuators go fully open for a long time (hours), then start to set the flow rate.

 

The other mod I made, was to remove all outside control from the ASHP, the only influence is the WC curve. So it starts and stop as it wants.  Moved the house thermostat to control the two mixer valve set points (via a volt free switch on the controller), instead of when the heat pump runs.

 

Mixer valve control set point T, is set to a flow temp of 27 and T2 set to 38 (so it goes to a fully open position). Used the thermostat timer to have a target of 19.5 for 07.30 to midnight and 20.5 during E7 time period.

 

So running regime is, no call for heat - UFH pump stays running and mixer valve modulates to keep flow at 27 degs, call for heat - mixer goes fully opens take all the heat the ASHP is delivering into the floor.

 

Outside temp has been a steady 5 degs, from last year's monitoring, I found the calculation of house heat loss to be very accurate.  So for the last 24 hrs the CoP including DHW has been around 4.5.

 

Maybe a little fine tuning of the WC curve as temperature drops, but quite happy at the moment.

 

Pipes now insulated

Edited December 9, 2023 by JohnMo

[JohnMo]

Since the last post I have added a few more Salus self balancing actuators, they seem to do a good job of leveling out the energy going into the floor. The heat pump has settled down to a very rhythmic pattern of run - stop, the temperature going into the UFH although set for 28, goes 28 when heat pump is on and reduces down to 25 when heat pump off. The Salus actuator has a similar pattern of going fully open at 25 and then controlling dT at 28 and bringing the flows rates down again.

 

Here is plot of the hall temperature, which shows really stable temperatures, the slight dip in temperature between 8 and 9am is 2 hours after DHW heating started, the hall temp drops 0.1 degs, then based on yesterday's data, recovers over the next couple of hours.

 

 

So far the high flow temp setting (up to 36 deg based on WC curve) hasn't kicked in, OAT, has varied between 3 and 8 degs. Have -1 forecast for tonight so will see how or if things change.

[JohnMo]

Energy usage comparison based on real energy consumption. During the last 48hrs no other heating sources have been used just the heat pump.

 

Garden room was averaging around 7kWh per day for heating, using direct electric heating. This has reduced to zero for the keeping warm (via direct heating), when in use I will still use direct heating for now.

 

Last 48hrs has averaged 18kWh a day (between 3 and 8 degrees, wet and overcast), for house heating at a continuous 20.5, garden room heating was at 14-15 degrees and providing all DHW.  Almost all energy is coming from cheap rate (15.16p per kWh), via E7 overnight and a battery in the daytime.

 

Calculated heat loads at an average 5 degrees OAT

House 56kWh day (found similar gas usage last year)

Garden room 7kWh (based on previous direct electric consumption)

DHW 7 kWh - (based on previous usage patterns)

 

total 70kWh heating demand, electricity consumed by heat pump is 18kWh, overall CoP of 3.88.

 

Gas price 6.489p assuming 100% efficiency 70x0.06489 would be £4.54 per day, would cost more if less efficient

E7 Electric with battery 18 x 0.1516 is £2.73.

 

40% cost saving.

[Andehh]

Interesting read! Please keep us updated with the performance!

[JohnMo]

Was down to -1 last night the air very wet, house temp stayed pretty constant with the 28 deg flow temp, but summer house dropped 2 degs, so have added a couple of degrees to the end of the WC curve to compensate.

 

Interesting there was only one defrost cycle all night. Think the ASHP is able to modulate down much further with the continuous drip feeding of heat into the house, so doing very little work.

[ReedRichards]

5 hours ago, JohnMo said:

have added a couple of degrees to the end of the WC curve to compensate.

 Are you able to do this?  My WC "curve" is constrained to be a straight line, whereas I think it probably needs a kink in it around 0 to allow for time spent defrosting.

[JohnMo]

18 minutes ago, ReedRichards said:

 Are you able to do this?  My WC "curve" is constrained to be a straight line, whereas I think it probably needs a kink in it around 0 to allow for time spent defrosting.

It is also a straight line

 

So I have added 2 degs to B10. Moved from 7 to 9 degs.

 

My current curve is

B10 9.0
B12 8
B14 (-)16
Hea 33.5

 

So starts at +8 degs and down to -8 OAT. At +8 and above flow temp is 33.5 degs and at -8 it's at 42.5 deg flow temp.

 

26 minutes ago, ReedRichards said:

kink in it around 0 to allow for time spent defrosting

A kink would be better or even an additional set point at zero so it was two flat or the software made a nice curve.

[ReedRichards]

Funny that this isn't a routine feature of heat pumps.  It almost seems like they copied what gas boilers do without thinking it through.  Either that or most other climates are dry enough that defrosting is much less of an issue.  

[JohnMo]

So garden room UFH, although just about works, really isn't much use at heat pump temperatures.

 

So a bit of research later, have purchased a fan coil unit. A Myson iVector MK2. Bargain from eBay, about a 1/3 the normal price.

 

It is a 4 pipe fan coil, so has two heat exchanges, one for heating and one for cooling, I will pipe both heat exchanges to a single pipe in a parallel. This should increase heat transfer area and hopefully be able to run slightly cooler.

 

Fan coils come with a temperature sensor, and the normal set point is 32 degrees for the fan to start. So the water has to be above 32 degs to get the heater running.  But the Myson one has an adjustable set point, so should simplify setup.

 

So far have mounted it on the wall. Intend to use the UFH manifold to feed the fan coil, with the Salus actuators to manage a 7 deg dT.

 

Heater on wall, with cover off and on

 

[JoeBano]

I was keeping an eye on that myson Ivector on eBay. They are soo expensive! I’ll be interested in the cooling as my house struggles to remove the heat in the hot summer days, I’ve been looking into these units for sometime.