PIV, heating and cooling: pros and cons, can and can't

[Garald]

[So, I am still on the look for a heat-pump installer, though by successive approximations I may be getting close to the goal. I am now talking to one who is offering a reasonable price for a Mitsubishi ("reasonable" compared to what I've been offered elsewhere) and who seems reasonably honest for a couple of reasons: he's downgraded his original off-the-cuff estimate on the power required to heat the place, and he's also honestly arguing why a Mitsubishi heat-pump (the only kind he sells, AFAIK) can't do, or shouldn't do, something that I was interested in having it do, and that, if I insist on it, I should look into Panasonics (presumably elsewhere).]

 

I am going to have Positive Input Ventilation (PIV) - that's has been the plan all along, and, if I understand correctly, ventilation is one of the things my architect does very well, as opposed to the other kind of thing.

 

The question is then how to couple it with heating (or cooling). I can't very well extract heat from the output as in non-PIV ventilation systems ("negative input ventilation"?), so the question is what do I do with the air the PIV takes in.

 

Enter Hydro'R/Aquarea:

https://www.vmi-technologies.com/wp-content/uploads/2020/09/aquarea-purevent-visionR.pdf

https://www.ventilairsec.com/wp-content/uploads/2019/11/VisionR_16pages_BAT-BD.pdf

https://www.ventilairsec.co.uk/products/range-vmi/

 

- the idea being to preheat or cool air coming into the house through the PIV.

 

Cooling air coming in using cold water produced by a heat pump. You can see the system has a maximal capacity of 800W in cooling - really not much, so it can't make that much of a difference.

More than one installer has expressed skepticism or puzzlement about the possibility of using a non-Panasonic system for cooling. Now I've come across an installer with what sounds like good reasons for having that attitude: apparently, Panasonic compressors tolerate a greater number of restarts (their documentation states that they tolerate being restarted up to 11 times per hour, as opposed to 6 times per hour) - and that makes them usable for cooling a rather small flow of water. (The installer is also a bit skeptical about whether that can really be great for the longevity and efficiency of a Panasonic system.)

 

Preheating air coming in using hot water produced by a heat pump - pretty much like any other radiator. I may yet convince the installer to try his hand at that; it's difficult to see how it is different from any other radiator. (He just warns me that it would then be regulated by the same thermostat as the "normal" radiators - how is that a problem, though? )

 

At the same time, I wonder: how much does preheating air actually help with efficiency? From the moment that new air enters a room, it is no less likely to be expelled at any given moment than any other ("stale") air.

 

What is your take?

 

 

[Duncan62]

I'm not technical but very interested in your idea.

 

Could you run the heating part from the hot water cylinder, then the hp is not constantly cycling?

Might make the cooling more complicated to implement as it would require a separate loop running off the hp anyway?

Edited February 11, 2023 by Duncan62
Typo

[Garald]

1 hour ago, Duncan62 said:

I'm not technical but very interested in your idea.

 

Could you run the heating part from the hot water cylinder, then the hp is not constantly cycling?

 

What's the problem will letting the heat pump's thermostat determine whether the VMI's heater gets hot water? I don't see how that's grossly suboptimal from the point of view of the VMI, and of course it means the heat pump doesn't get abused.

 

1 hour ago, Duncan62 said:

Might make the cooling more complicated to implement as it would require a separate loop running off the hp anyway?

 

[Nickfromwales]

2 hours ago, Duncan62 said:

Could you run the heating part from the hot water cylinder

The DHW cylinder is full of potable water which cannot go anywhere else than the hot water taps / outlets, and that is propelled by cold mains pressure feeding into the cylinder. The heat from the ASHP heats this via a sealed and independent coil. These are two separate bodies of water at two completely different pressures / potentials.

What you are likely thinking about doing is achieved by using a buffer tank with multiple tappings, in addition to a DHW cylinder.

 

[Archer]

@Garald - Sorry to resurrect your thread, but did you end up installing the VMI Purevent HydroR unit in the end?   

 

Looks very interesting for the setup that we have but it's a French company so not easy to find importers/ suppliers etc. If you went with this, any feedback on how it works or any alternative, similar PIV systems you found that can pre-heat and dehumidify? 

[Garald]

Yes, it's installed now - but we've chosen to activate only the pre-heating, not the cooling. The heat-pump installer contacted Mitsubishi technical support, which advised us against using cooling - the heat pump would have been forced to switch between cooling and heating functions too frequently. So, in the end, we went with a heating-only heat pump.

 

Not sure how much the VMI unit is supposed to dehumidify. Of course it does filter air (a good idea in the Paris area!).

 

 

[Ewan]

On 17/05/2023 at 11:07, Garald said:

Yes, it's installed now - but we've chosen to activate only the pre-heating, not the cooling. The heat-pump installer contacted Mitsubishi technical support, which advised us against using cooling - the heat pump would have been forced to switch between cooling and heating functions too frequently. So, in the end, we went with a heating-only heat pump.

 

Not sure how much the VMI unit is supposed to dehumidify. Of course it does filter air (a good idea in the Paris area!).

 

 

 

interesting, they considering the DHW cycle to be problem even though it can be done in one go at night when cooling is less likely to be used?

[JohnMo]

That's a couple threads I have seen on here where mitsubishi pushed back on cooling.

 

Mine (not mitsubishi) starts the day on cooling about 9am does DHW, then when that's done reverts happy to cooling again, for the rest of the day. Next day repeats.

[Ewan]

Yes does seem like a bit of a weird stipulation.

What do you use for cooling? UFH?

[JohnMo]

I use UFH. Not as good as Aircon, but takes the edge of the temp and stops us melting completely, unlike last year every time the sun came out.

[joth]

Very interesting. I have my mitsubishi ecodan set to cooling, it was extremely inefficient but this was mismatched emitters (1kW FCU on a 8.5kW heatpump) not specifically from the mode changes. (the heatpump was sized for the UFH and the FCU was an afterthought).

I've now added a 100L buffer tank, and a shed load of logic in Loxone to correctly manage the hysteresis needed for the FCUs only, and cooling is running very well now.

I currently have the DHW charge up twice a day (4am Octopus cheap rate, and 1pm top up to maximize solar PV/battery use). Perhaps I'll click it back to once a day and rely on the PV diverter for daytime top up, if the mode change is indeed an issue.

 

Over all if I had my time again, I'd just use the a2w for DHW and UFH (space heating only) and add a multi-split a2a upstairs for cooling (and backup heating)

 

[markocosic]

25 minutes ago, joth said:

Very interesting. I have my mitsubishi ecodan set to cooling, it was extremely inefficient but this was mismatched emitters (1kW FCU on a 8.5kW heatpump) not specifically from the mode changes. (the heatpump was sized for the UFH and the FCU was an afterthought).

I've now added a 100L buffer tank, and a shed load of logic in Loxone to correctly manage the hysteresis needed for the FCUs only, and cooling is running very well now.

I currently have the DHW charge up twice a day (4am Octopus cheap rate, and 1pm top up to maximize solar PV/battery use). Perhaps I'll click it back to once a day and rely on the PV diverter for daytime top up, if the mode change is indeed an issue.

 

Over all if I had my time again, I'd just use the a2w for DHW and UFH (space heating only) and add a multi-split a2a upstairs for cooling (and backup heating)

 

Or build for a smaller heat loss / larger solar gain and use +3 kW / -2 kW for everything?

[joth]

2 minutes ago, markocosic said:

 

Or build for a smaller heat loss / larger solar gain and use +3 kW / -2 kW for everything?

Well yes, with an open slate, not doing a retrofit in the middle of a town would alter a lot of parameters 

[markocosic]

19 minutes ago, joth said:

Well yes, with an open slate, not doing a retrofit in the middle of a town would alter a lot of parameters 

 

Ah!

 

I'm about to move the A2A upstairs in Cambridge and chuck in an A2W for rads and DHW downstairs (plus rads upstairs because there; but mainly for downstairs)

 

Will be a single head to upstairs landing though (open the doors during the day to cool); and would like to think I might get around to trying wet ceiling/wall heating downstairs (easier to retrofit as a plasterboard layer under a ceiling / onto a partition wall than it would be to wet UFH; and with higher output per m2 at a given flow temperature; albeit not as comfortable as UFH)

 

Not too dissimilar in conclusion. 🙂

[Ewan]

13 hours ago, joth said:

Very interesting. I have my mitsubishi ecodan set to cooling, it was extremely inefficient but this was mismatched emitters (1kW FCU on a 8.5kW heatpump) not specifically from the mode changes. (the heatpump was sized for the UFH and the FCU was an afterthought).

I've now added a 100L buffer tank, and a shed load of logic in Loxone to correctly manage the hysteresis needed for the FCUs only, and cooling is running very well now.

I currently have the DHW charge up twice a day (4am Octopus cheap rate, and 1pm top up to maximize solar PV/battery use). Perhaps I'll click it back to once a day and rely on the PV diverter for daytime top up, if the mode change is indeed an issue.

 

Over all if I had my time again, I'd just use the a2w for DHW and UFH (space heating only) and add a multi-split a2a upstairs for cooling (and backup heating)

 

We're in the depths of a deep retrofit and have UFH going in, rads upstairs. ASHP due in a later phase (don't ask 😄), so bit of time to plan cooling.

Had been looking at FCUs, but the complexity, lack availability of knowledge etc is off putting.

Why would you not use the UFH for cooling, in your hypothetical? The cool air coming down would be enough? ** edit, just realised this was @joth , not yourself **

We're also a bit stuck with west facing solar gain, but currently looking at designing in some external automatic blinds.

Multi splits should be minimally disruptive to install upstairs if needed after renovation is done... right... ?

 

@markocosic any chance you could explain the +3kW/-2kW thing for me? not sure what you mean there

Edited June 21, 2023 by Ewan

[Ewan]

13 hours ago, JohnMo said:

I use UFH. Not as good as Aircon, but takes the edge of the temp and stops us melting completely, unlike last year every time the sun came out.

How's the upstairs, do you feel the need for any active cooling up there? (or do you have UFH on all levels)

[JohnMo]

Only have a plant room upstairs, so all bedrooms are on ground floor. But wife wanted thick wool carpets in bedrooms, so UFH in bedrooms is pretty limited.

 

Have been debating a fan coil in the hall and lounge, but that will have to wait until next year.

[Ewan]

15 hours ago, markocosic said:

 

Ah!

 

I'm about to move the A2A upstairs in Cambridge and chuck in an A2W for rads and DHW downstairs (plus rads upstairs because there; but mainly for downstairs)

 

Will be a single head to upstairs landing though (open the doors during the day to cool); and would like to think I might get around to trying wet ceiling/wall heating downstairs (easier to retrofit as a plasterboard layer under a ceiling / onto a partition wall than it would be to wet UFH; and with higher output per m2 at a given flow temperature; albeit not as comfortable as UFH)

 

Not too dissimilar in conclusion. 🙂

Is this single air handler in the landing a strategy that comes recommended? Some results on google saying don't bother, but I guess if the house is well insulated, and you're blowing air into the bedrooms, roughly, it could make a difference?

[joth]

9 hours ago, Ewan said:

We're in the depths of a deep retrofit and have UFH going in, rads upstairs. ASHP due in a later phase (don't ask 😄), so bit of time to plan cooling.

Had been looking at FCUs, but the complexity, lack availability of knowledge etc is off putting.

Why would you not use the UFH for cooling, in your hypothetical? The cool air coming down would be enough? ** edit, just realised this was @joth , not yourself **

We're also a bit stuck with west facing solar gain, but currently looking at designing in some external automatic blinds.

Multi splits should be minimally disruptive to install upstairs if needed after renovation is done... right... ?

 

@markocosic any chance you could explain the +3kW/-2kW thing for me? not sure what you mean there

 

Originally used cooling through UFH only (2021). A few problems for us:

1. We don't have UFH upstairs, just down. This is perfect for heating, but useless for cooling upstairs 

2. All our overheating occurs upstairs

3. Even downstairs, we find it makes the tiles chilly and a layer of cold air about a foot high off the floor, bit need something else to agitate it about to actually achieve cooling. 

 

In a passive house (assuming you don't go au natural without any active heating/cooling) I think it's hard to go wrong with heating via UFH at the bottom of the house, and cooling via FCUs (preferably a2a) at the top of the house, and in any room critical to not overheat (e.g. office space) or that has variable target temperatures and you need fast response time in 

 

Edited June 21, 2023 by joth

[joth]

6 hours ago, Ewan said:

Is this single air handler in the landing a strategy that comes recommended? Some results on google saying don't bother, but I guess if the house is well insulated, and you're blowing air into the bedrooms, roughly, it could make a difference?

Personally I'd not bother, but we have cats and prefer to keep bedroom doors closed so need to actively circulate air around rooms. 

We have a large skylight over the hallway/landing that I've set to automatically open when needed for overnight purge ventilation, this cools the house down as a whole marvelously, but useless for occupied bedrooms. Ironically despite being on the second floor (vaulted ceiling) it cools the ground floor better than the first floor. Convection vs closed doors for you. 

 

[Ewan]

 

15 hours ago, joth said:

 

Originally used cooling through UFH only (2021). A few problems for us:

1. We don't have UFH upstairs, just down. This is perfect for heating, but useless for cooling upstairs 

2. All our overheating occurs upstairs

3. Even downstairs, we find it makes the tiles chilly and a layer of cold air about a foot high off the floor, bit need something else to agitate it about to actually achieve cooling. 

 

In a passive house (assuming you don't go au natural without any active heating/cooling) I think it's hard to go wrong with heating via UFH at the bottom of the house, and cooling via FCUs (preferably a2a) at the top of the house, and in any room critical to not overheat (e.g. office space) or that has variable target temperatures and you need fast response time in 

 

Thanks for the insight. A couple regular fans sound good for moving the cooler air around.

Got plans for shade that can be easily retrofitted to the west side where needed (fakro rooflight external solar shades are retrofitable, and some generic external window blinds I'm looking into), and a2a can be routed through the loft easily enough. Will see where our hot spots are next summer.

[joth]

5 hours ago, Ewan said:

 

Thanks for the insight. A couple regular fans sound good for moving the cooler air around.

Got plans for shade that can be easily retrofitted to the west side where needed (fakro rooflight external solar shades are retrofitable, and some generic external window blinds I'm looking into), and a2a can be routed through the loft easily enough. Will see where our hot spots are next summer.

Sounds good. We have automated shading, but the problem bedrooms all overheat due to human  bodies giving off heat, not much that can be done about that passively (we keep windows closed because busy train line, and doors closed because cats as mentioned).

Retrofitting an a2a with head unit in the room should be easier than retrofitting ducted fan coils. Only thing is to plan the condensate drain. You can use a pump for that if needed, but seems much more elegant to have it gravity drained if you can manage it

[Dan F]

We also have no UFH, fan coils or A2A upstairs.   We didn't plan for any of these because, in theory, the overheating risk with fully automatic blinds everywhere was extremely low.  The reality though is that overheating risk is based on <25C and night flushing.  But, up to 25C isn't comfortable and during a week-long heatwave, it doesn't get cool enough outside to flush out hot air.

 

We find that the first floor heats up due to three reasons (excluding solar gain)

- Through the fabric of the building

- Humans

- MVHR. (If the average house temperature is 22C and outside it's 37C, your MVHR unit is injecting air at 25C if your MVHR is 80% efficient).

 

To cool down the first floor to an ideal temperature we'd need to cool the ground floor to <20C probably, which then becomes uncomfortable downstairs.

 

We did install an MVHR post-heater as a backup plan and it does makes some impact, but it primarily stops MVHR from heating up the first floor rather than providing any kind of active cooling.  In order to try to use it to actively lower the first-floor temperature it needs to be run on boost and left on all day.   In this scenario though, part of the cooling power is wasted on cooling the additional incoming air that you wouldn't be cooling if you weren't running MVHR on boost.  I knew MVHR post-heater was minimally effective from the beginning, but I never realised that the cooling power from post-heat and fan-coil units was not at all comparable because one is cooling incoming air on boost and the other is cooling exiting room air.

 

 

Edited June 22, 2023 by Dan F

[Ewan]

On 22/06/2023 at 18:45, Dan F said:

We also have no UFH, fan coils or A2A upstairs.   We didn't plan for any of these because, in theory, the overheating risk with fully automatic blinds everywhere was extremely low.  The reality though is that overheating risk is based on <25C and night flushing.  But, up to 25C isn't comfortable and during a week-long heatwave, it doesn't get cool enough outside to flush out hot air.

 

We find that the first floor heats up due to three reasons (excluding solar gain)

- Through the fabric of the building

- Humans

- MVHR. (If the average house temperature is 22C and outside it's 37C, your MVHR unit is injecting air at 25C if your MVHR is 80% efficient).

 

To cool down the first floor to an ideal temperature we'd need to cool the ground floor to <20C probably, which then becomes uncomfortable downstairs.

 

We did install an MVHR post-heater as a backup plan and it does makes some impact, but it primarily stops MVHR from heating up the first floor rather than providing any kind of active cooling.  In order to try to use it to actively lower the first-floor temperature it needs to be run on boost and left on all day.   In this scenario though, part of the cooling power is wasted on cooling the additional incoming air that you wouldn't be cooling if you weren't running MVHR on boost.  I knew MVHR post-heater was minimally effective from the beginning, but I never realised that the cooling power from post-heat and fan-coil units was not at all comparable because one is cooling incoming air on boost and the other is cooling exiting room air.

 

 

 

 

On 22/06/2023 at 16:47, joth said:

Sounds good. We have automated shading, but the problem bedrooms all overheat due to human  bodies giving off heat, not much that can be done about that passively (we keep windows closed because busy train line, and doors closed because cats as mentioned).

Retrofitting an a2a with head unit in the room should be easier than retrofitting ducted fan coils. Only thing is to plan the condensate drain. You can use a pump for that if needed, but seems much more elegant to have it gravity drained if you can manage it

 

So looks like the options available to us at this point (back to brick and no plumbing in yet) would be:

 

• Using A2W: UFH cooling downstairs, wall mounted FCUs upstairs for heating and cooling. Maybe a ceiling mounted FCU downstairs for cooling if UFH cooling is not enough. Could do this with A2W as long as all copper is insulated and drainage provisioned.
• Using A2W & A2A: UFH cooling downstairs, A2A wall mounted units upstairs (or ducted...) as well as radiators. Do a2a air handlers still need condensate drains?

I was hoping to get it all done by the a2w HP if possible, but it may not necessarily be the most economical or less complex route, even though one unit doing everything sounds appealing.

[Duncan62]

On 13/07/2023 at 15:17, Ewan said:

 

 

 

So looks like the options available to us at this point (back to brick and no plumbing in yet) would be:

 

• Using A2W: UFH cooling downstairs, wall mounted FCUs upstairs for heating and cooling. Maybe a ceiling mounted FCU downstairs for cooling if UFH cooling is not enough. Could do this with A2W as long as all copper is insulated and drainage provisioned.
• Using A2W & A2A: UFH cooling downstairs, A2A wall mounted units upstairs (or ducted...) as well as radiators. Do a2a air handlers still need condensate drains?

I was hoping to get it all done by the a2w HP if possible, but it may not necessarily be the most economical or less complex route, even though one unit doing everything sounds appealing.

 

Thanks for the summary @Ewan, did you come to a conclusion for installation?