ASHP vs GSHP

[IanR]

1 hour ago, pdf27 said:

Planning for warming the house up again after a heating failure during a cold snap is overkill for me

 

But installing a GSHP and ground loops for unrequired cooling isn't  

 

Joking aside, I have a 12kW HP and my PHPP calcs estimated a worst case 6.4kW heat loss. My HP has an easy time, the house performs slightly better than PHPP calculated, although not PHPP's mistake, I make better use of solar gain than PHPP had allowed for.

 

Even with an oversized HP, the house can still be slow to react. This is all my own fault, as I don't allow the HP to heat the house in the morning if the forecast is either sunny or only partially cloudy, knowing that by 11:00 an average house temp that was say 19.5 @ 07:00 will be sailing passed 21.5, without the heating on. On the days the forecast is wrong or mis-timed it has a bit of catch up to do, and when it does it takes a little while to do so.

 

I should be clear, if I wasn't playing games trying to predict the solar gain, and allowed the heating system to maintain a constant temperature, this wouldn't typically be an issue.

 

Similarly, cooling is effected in the same way, but more acutely. Solar gain is far more powerful that heat loss, so is able to rapidly change the internal temperature. If it is "allowed" to get to 30, it will take a long time for the ASHP to bring it back down, and will generally have to wait till the evening ambient temp drops to allow our stack ventilation to dump heat out the roof vents. This has taken quite a lot of tinkering with to get UFH circulation, external blinds, and roof vents working to minimise the solar gain so that the HP can do the rest, but it is not always successful.

[Omnibuswoman]

18 hours ago, SteamyTea said:

Are you going to get an interim airtightness test before you close everything up?

yes we will, just to be sure. I’ve read horror stories of errors that have only been detected after completion leaving the house under-heated. 

[SteamyTea]

2 minutes ago, Omnibuswoman said:

yes we will, just to be sure. I’ve read horror stories of errors that have only been detected after completion leaving the house under-heated. 

Not the underheating that is the problem, that can be cured with a bigger heater, it is the problem of just throwing the energy out the door and making the MVHR not so efficient.

[pdf27]

13 hours ago, Dan F said:

GSHP for heating + ASHP for cooling, or did I misunderstand?

Nope, what we're thinking of is using an ASHP instead of a GSHP if the quotes come back too high. We'd prefer a GSHP, but aren't prepared to pay very much of a premium for it (say £2-3k). Cooling is mandatory, whether we get a GSHP or ASHP.

 

13 hours ago, SteamyTea said:

No it don't, it has a reasonably high specific heat capacity when wet.  About a third of what water has (as long a sit is not frozen, or steam)

Apologies, that was poorly phrased. The point I was trying to convey is that the time constant for a ground loop is very long - the specific heat capacity is very high compared to the thermal conductivity. This means that ground loops are sized for the total heat demand over a significant period of time (i.e. primarily on ground thermal conductivity - it comes directly into the sizing calculation), rather than that found in a cold snap. Essentially you end up with a system with a great deal of thermal inertia on the ground loop and thus a COP unaffected by cold snaps.

 

11 hours ago, IanR said:

But installing a GSHP and ground loops for unrequired cooling isn't  

Nah, the reasoning that we're interested in a GSHP is independent of the reason that cooling is mandatory.

 

11 hours ago, IanR said:

Joking aside, I have a 12kW HP and my PHPP calcs estimated a worst case 6.4kW heat loss. My HP has an easy time, the house performs slightly better than PHPP calculated, although not PHPP's mistake, I make better use of solar gain than PHPP had allowed for.

I'm wary of oversizing the heat pump. Quite apart from the cost impact, the smaller the heat pump the easier it looks like it will be to control. Additionally, if modelling with PHPP using somebody competent then we shouldn't need much margin - although as noted PHPP should predict a heat load of about 2kW, and the smallest available heat pump would be 3kW, so 50% margin.

 

11 hours ago, IanR said:

Even with an oversized HP, the house can still be slow to react. This is all my own fault, as I don't allow the HP to heat the house in the morning if the forecast is either sunny or only partially cloudy, knowing that by 11:00 an average house temp that was say 19.5 @ 07:00 will be sailing passed 21.5, without the heating on. On the days the forecast is wrong or mis-timed it has a bit of catch up to do, and when it does it takes a little while to do so.

 

I should be clear, if I wasn't playing games trying to predict the solar gain, and allowed the heating system to maintain a constant temperature, this wouldn't typically be an issue.

 

Similarly, cooling is effected in the same way, but more acutely. Solar gain is far more powerful that heat loss, so is able to rapidly change the internal temperature. If it is "allowed" to get to 30, it will take a long time for the ASHP to bring it back down, and will generally have to wait till the evening ambient temp drops to allow our stack ventilation to dump heat out the roof vents. This has taken quite a lot of tinkering with to get UFH circulation, external blinds, and roof vents working to minimise the solar gain so that the HP can do the rest, but it is not always successful.

What I have in mind is not dissimilar, but probably a bit simpler. Essentially the plan is to turn the thermostat up one degree when electricity is cheap (mostly from PV but also when it's windy in winter) as well as shift the time clock for the hot water cylinder around the same way, and otherwise leave it to do it's own thing. Given the location and alignment, we're quite likely to go for the 10W/m² criteria rather than the 15 kWh/m²/year one to avoid getting too much solar gain which should also help a bit with the summer overheating.

[puntloos]

Speaking on the subject of cooling, some people handwave it away saying that you can just 'reverse' the ASHP/GSHP (it's more a rerouting of pipes) and it will pump chilled water. 

 

The big issue as I understand it, is condensation. Some people told me that with ASHP-level water, which isn't super cold, it's actually not an issue. Some others insist that some cold water coolers might be the better approach.

 

more detail:

 

[joth]

1 hour ago, puntloos said:

Speaking on the subject of cooling, some people handwave it away saying that you can just 'reverse' the ASHP/GSHP (it's more a rerouting of pipes) and it will pump chilled water. 

 

On a ASHP this is quite achievable: on the Mitsubishi FTC6 you flip dipswitch SW2-4, power cycle it, use the controller to set it to Cooling rather than Heating mode, adjust the flow temperature as desired. Cooling, with no hands waved.

 

1 hour ago, puntloos said:

The big issue as I understand it, is condensation. Some people told me that with ASHP-level water, which isn't super cold, it's actually not an issue. Some others insist that some cold water coolers might be the better approach.

 

 

There's basically places the condensation can form: on the emitters, and on all the intermediary pipework.

If putting cooling through the UFH, there's a small risk of condensation forming in the screed or between screed and finishes. This can crack or rot wood etc. Bad bad, must be avoided by running it no colder than about 14 degrees IIRC

Pipework condensation can be designed out: make sure it's all installed with high quality contiguous thick insulation, e.g. armaflex, no air allowed to touch the pipes, and there shouldn't be any way for the condensation to form.

 

The fancoil linked is not so much about either these issues per-se, as it's just more effective and comfortable to use. In our house the  downstairs remains fairly cool, and the  ground floor floor-finishes themselves doubly so. The overheating occurs high up on the first floor. Much more effective to drop cold air from above on the house than try and cool it from below. Also, yeah the fan coil has a condensation drip tray and can run at 5 degrees C fine.

So I plan to only use UFH for heat and the fancoil to cool.

 

Unfortunately, there's no way to set this in the FTC6 -- both zones must be in heating or cooling, can't mix, and there's no electronic input to select hot vs cold, so I'm left doing an annual manual switcheroo from heat mode to cooling mode and back again. (The MELcloud API obviously supports doing this as the Android app does let you do this remotely, but unfortunately the home assistant plugin doesn't support it. Maybe before heating season starts again they'll fix this, or I'll see if I can!!)

 

 

 

 

 

Edited May 19, 2021 by joth

[puntloos]

1 hour ago, joth said:

On a ASHP this is quite achievable: on the Mitsubishi FTC6 you flip dipswitch SW2-4, power cycle it, use the controller to set it to Cooling rather than Heating mode, adjust the flow temperature as desired. Cooling, with no hands waved.

 

Yep. I believe you mentioned this before, I'm still somewhat struck by how 'hard' it is, but I believe you said it's more a regulatory thing than technology.

 

1 hour ago, joth said:

 

There's basically places the condensation can form: on the emitters, and on all the intermediary pipework.

If putting cooling through the UFH, there's a small risk of condensation forming in the screed or between screed and finishes. This can crack or rot wood etc. Bad bad, must be avoided by running it no colder than about 14 degrees IIRC

Pipework condensation can be designed out: make sure it's all installed with high quality contiguous thick insulation, e.g. armaflex, no air allowed to touch the pipes, and there shouldn't be any way for the condensation to form.

I suppose it does add a lot of potential failure points if people mess about. Still just a couple of fan coils in the loft might work somehow. 

 

 

1 hour ago, joth said:

 

The fancoil linked is not so much about either these issues per-se, as it's just more effective and comfortable to use. In our house the  downstairs remains fairly cool, and the  ground floor floor-finishes themselves doubly so. The overheating occurs high up on the first floor. Much more effective to drop cold air from above on the house than try and cool it from below. Also, yeah the fan coil has a condensation drip tray and can run at 5 degrees C fine.

But does the ASHP generate water that cold?

 

1 hour ago, joth said:

So I plan to only use UFH for heat and the fancoil to cool.

 

Unfortunately, there's no way to set this in the FTC6 -- both zones must be in heating or cooling, can't mix, and there's no electronic input to select hot vs cold, so I'm left doing an annual manual switcheroo from heat mode to cooling mode and back again. (The MELcloud API obviously supports doing this as the Android app does let you do this remotely, but unfortunately the home assistant plugin doesn't support it. Maybe before heating season starts again they'll fix this, or I'll see if I can!!)

 

I suppose the switch only has to happen twice a year or perhaps 4-6 times in dire need, but still, weird tha

[IanR]

41 minutes ago, puntloos said:

Yep. I believe you mentioned this before, I'm still somewhat struck by how 'hard' it is, but I believe you said it's more a regulatory thing than technology.

 

I suppose it does add a lot of potential failure points if people mess about. Still just a couple of fan coils in the loft might work somehow. 

 

I suppose the switch only has to happen twice a year or perhaps 4-6 times in dire need, but still, weird tha

 

If you haven't purchased an ASHP yet, and you want cooling, just purchase one that offers cooling out of the box

 

The requirement to "hack" existing ASHPs to gain the cooling function stems back to the RHI scheme not allowing HPs that could be used in a cooling mode. Manufactures then had to disable the function for the UK market that was available in other territories.

 

RHI changed in 2017/8 to allow HPs with cooling so more ASHPs with cooling should be available in the UK market. The Nibe F2040 series is the one I have, but I'm sure there must be others.

 

[puntloos]

53 minutes ago, IanR said:

 

If you haven't purchased an ASHP yet, and you want cooling, just purchase one that offers cooling out of the box

 

The requirement to "hack" existing ASHPs to gain the cooling function stems back to the RHI scheme not allowing HPs that could be used in a cooling mode. Manufactures then had to disable the function for the UK market that was available in other territories.

 

RHI changed in 2017/8 to allow HPs with cooling so more ASHPs with cooling should be available in the UK market. The Nibe F2040 series is the one I have, but I'm sure there must be others.

 

How did you wire up the cooling bit? Are you just using the UFH or all types of chiller coils?

[IanR]

13 minutes ago, puntloos said:

How did you wire up the cooling bit? Are you just using the UFH or all types of chiller coils?

 

If I've understood the "wiring up" question, the Controller (SMO40) comes all set to run Heating, Cooling and Hot water, so its just a comms line from controller to HP.

 

I run mine either heating or cooling the buffer. The buffer then feeds the UFH and a heat exchanger on the MVHR supply duct.

Edited May 19, 2021 by IanR

[puntloos]

12 minutes ago, IanR said:

 

If I've understood the "wiring up" question, the Controller (SMO40) comes all set to run Heating, Cooling and Hot water, so its just a comms line from controller to HP.

 

I run mine either heating or cooling the buffer. The buffer then feeds the UFH and a heat exchanger on the MVHR supply duct.

 

Ah so both UFH (any condensation concerns? How did you pre-empt them hopefully?) as well as heat exchangers? In day to day do they actually meaningfully work? Some people say MVHR is too low power to respond quickly to overheating challenges

[IanR]

Just now, puntloos said:

 

Ah so both UFH (any condensation concerns? How did you pre-empt them hopefully?) as well as heat exchangers? In day to day do they actually meaningfully work? Some people say MVHR is too low power to respond quickly to overheating challenges

 

The MVHR can not move a sufficient volume of air to cool the house, but it can assist the UFH a small amount (~ 1kW)

 

To avoid condensation on the floors, you can't chill them below the dew point. The due point varies with air temp and relative humidity. You could set an overriding minimum temp for the buffer, say 13 or 14 degrees C, if you wanted to just rely on the ASHP controls, or if you had some other automation that could put some logic into the temperature and an RH sensor as well as temperature, you could let it calculate how low you could take the floor temperature to improve on the 13 or 14 degrees.

 

The downside of UFH cooling, compared to an AC unit, is the time it takes to react. You can't let the temperature rise by 5 - 10 degrees above target and expect the UFH to bring that down in an hour. The cooling needs to start it's job as soon as the temp moves above target.

I've no experience of the chiller units, but I'd expect them to provide a much more noticeable temp reduction in the room they are situated, as they are working directly on the air in the room, and air holds a lot less energy than the concrete slab. You could potentially also run the chiller with cooler water as the condensation is more manageable. However when you switch the chiller off I'd expect the air will warm back up quite quickly as the fabric of the house won't have been cooled by much.

 

 

[dpmiller]

I had a "play" with the cooling mode on our unit a couple of days ago. A couple of button presses enabled it, and it happily chilled down to a flow temp of 12c shedding loads of heat outside.

[Dan F]

2 hours ago, dpmiller said:

I had a "play" with the cooling mode on our unit a couple of days ago. A couple of button presses enabled it, and it happily chilled down to a flow temp of 12c shedding loads of heat outside.

 

Challenge with cooling can be control.  While most ASHP's have a dry contact "call for heat", for cooling my understanding is you need to rely on manufactuers thermostats rather than control from home automation.  Any one else have any experience of this?

[joth]

9 hours ago, puntloos said:

But does the ASHP generate water that cold?

 

Haven't tested the limit yet, but 5°C is the minimum setting the UI allows

1 hour ago, Dan F said:

Challenge with cooling can be control.  While most ASHP's have a dry contact "call for heat", for cooling my understanding is you need to rely on manufactuers thermostats rather than control from home automation.  Any one else have any experience of this?

 

Yes, mentioned briefly upthread, but with ecodan FTC6, the call for heat dry contact inputs become call for cool when in cooling mode. The challenge is switching mode: can be done in the Mitsubishi controller UI or their phone app, but not via a simple electrical input. However it does have a cooling mode active output, so I'm thinking about feeding that back to loxone so it at least knows what result it of going to get when it calls for heat or cold, and locks out the other logic as appropriate.

If I can fix the missing feature in the home assistant plugin I maybe able to programmatically change mode too.

 

 

 

 

 

 

 

Edited May 20, 2021 by joth

[IanR]

7 hours ago, Dan F said:

 

Challenge with cooling can be control.  While most ASHP's have a dry contact "call for heat", for cooling my understanding is you need to rely on manufactuers thermostats rather than control from home automation.  Any one else have any experience of this?

 

I keep the Nibe controller in Manual mode and use the MODBUS add-on to allow Loxone to send an "allow cooling" and "allow heating" instruction.

 

It could be done directly on the Nibe SMO 40 controller in Auto mode and setting a "Cool/Heat set point" to change the mode and a "Cool at room over" temp for when to start cooling.

Edited May 20, 2021 by IanR

[Dan F]

10 hours ago, IanR said:

I keep the Nibe controller in Manual mode and use the MODBUS add-on to allow Loxone to send an "allow cooling" and "allow heating" instruction.

 

That sounds like exactly what I need.  Already gone down the Vaillant route though..   In theory they have API/Modbus/EEBus interfaces in progress, but nothing yet.. unless I try to do it myself via an ebus coupler: https://www.esera.de/shop/en/products/ebus/135/ebus-coupler-usb