Fan Coil Units for use with a (cooling) ASHP

[NCXo82ike]

11 minutes ago, JohnMo said:

Bungalow so ground floor only. 192m² area, UFH at 300mm centres. 200mm PIR with UFH pipes stapled to insulation. 100mm concrete screed. Summer house also well insulated.

is the summer house also UFH? How do you take the water loop from your house to the summer house, and how far is it?

[Wil]

Just for completeness, I email Megawave about their FCUs and got the following data sheets if anyone is still considering them:

 

I haven’t gone as far as an order.

FCU Data.pdf MWES Concealed FCU data sheet.pdf MW Free Standing- FCU（DC motor）manaul 23.6 wifi 1.pdf

[Ommm]

36 minutes ago, Wil said:

Just for completeness, I email Megawave about their FCUs and got the following data sheets if anyone is still considering them:

 

I haven’t gone as far as an order.

FCU Data.pdf 659.83 kB · 0 downloads MWES Concealed FCU data sheet.pdf 7.16 MB · 0 downloads MW Free Standing- FCU（DC motor）manaul 23.6 wifi 1.pdf 1.03 MB · 0 downloads

Those datasheets look very much like the ones from YESNCER.

 

The controller looks like an off the shelf wifi+Tuya unit.  I can't find an exact match out of the many on Aliexpress ('fan coil controller') but it fits in a standard 86mm square switch wall box - on the concealed unit it'll be mounted on the wall in one of those, while in the radiator unit there's a space on the top.  They are typically interchangeable - some of them have RS485 so can be talked to via Modbus, although I'm not sure if the register list is published (I bought one from Aliexpress to play with but haven't used it thus far). It's a standard ESP8266 chip inside and there may be third party firmware replacements too (mine is the BAC-1000-ALW which is supported by WThermostatBeca).

Edited September 19 by Ommm

[NCXo82ike]

25 minutes ago, Ommm said:

Those datasheets look very much like the ones from YESNCER.

 

The controller looks like an off the shelf wifi+Tuya unit.  I can't find an exact match out of the many on Aliexpress ('fan coil controller') but it fits in a standard 86mm square switch wall box - on the concealed unit it'll be mounted on the wall in one of those, while in the radiator unit there's a space on the top.  They are typically interchangeable - some of them have RS485 so can be talked to via Modbus, although I'm not sure if the register list is published (I bought one from Aliexpress to play with but haven't used it thus far). It's a standard ESP8266 chip inside and there may be third party firmware replacements too (mine is the BAC-1000-ALW which is supported by WThermostatBeca).

I initially thought 3 fan speeds seems a little basic, however the panasonic FCUs are only 4 speed https://www.bpcventilation.com/panasonic-fan-coil-unit

[Ommm]

13 minutes ago, NCXo82ike said:

I initially thought 3 fan speeds seems a little basic, however the panasonic FCUs are only 4 speed https://www.bpcventilation.com/panasonic-fan-coil-unit

It's a (brushless?) DC fan controlled by a 0-10V DC speed input, so in theory if you apply an analogue voltage you can have any speed.  The controllers are often designed for AC fans which have three mains inputs which you energise in different combinations for slow/med/fast and I suppose they carry that over - makes the displays and UI the same.

Personally speaking I'd probably want some control with a slow fan ramp, eg if the thermostat decides the FCU to come on then gently ramp up the fan speed to target, rather than having it click on, and only spin as fast as needed (like the fan in a laptop etc).  That's why I think the replacement firmware is useful, because it allows you to program that kind of thing.

Edited September 19 by Ommm

[Wil]

49 minutes ago, Ommm said:

The controller looks like an off the shelf wifi+Tuya unit.

Yep, I’ve got one of these controlling the Cool Energy Reverso unit I’ve got. Works well enough and integrates with Home Assistant ok. You can have it in auto or always set to one speed so leaving it on minimum means noise isn’t an issue.

[JohnMo]

2 hours ago, NCXo82ike said:

is the summer house also UFH? How do you take the water loop from your house to the summer house, and how far is it?

Just use a fan coil in summer house. 15mm tee'ed into main flow lines from ASHP to house. About 12m of pipe in each direction.

[JohnMo]

47 minutes ago, NCXo82ike said:

initially thought 3 fan speeds seems a little basic, however the panasonic FCUs are only 4 spee

My Myson fan coil has multiple speeds, but just set mine on speed 1 and leave it. Water is always being circulated in either heat or cooling mode. Just use it like a radiator on weather compensation. Find that works best, zero thought.

[Dave Jones]

overthinking it. just leave them on auto with a fan on/off temp set then let the heat pump control them.

[NCXo82ike]

So all of this has confirmed for me that a comfopost isn't worth it for us.

 

If you're running fancoils on the same loop as UFH, presumably that gives plenty of circulating volume. It would then run offset above the dew point, accepting achieving less than maximal cooling/heating output from the fan coils.

 

It seems to me there's little point in running insulated pipe to supply the fan coils?

 

And is there any need then to provide a condensate drain for the fan coils?

[G and J]

34 minutes ago, NCXo82ike said:

So all of this has confirmed for me that a comfopost isn't worth it for us.

 

If you're running fancoils on the same loop as UFH, presumably that gives plenty of circulating volume. It would then run offset above the dew point, accepting achieving less than maximal cooling/heating output from the fan coils.

 

It seems to me there's little point in running insulated pipe to supply the fan coils?

 

And is there any need then to provide a condensate drain for the fan coils?

I don’t know the answers to those questions.

 

So I’m going to try to allow for all eventualities where I can without wasting tons of money.

 

I’m putting a Fancoil into our bedroom, with a drain and also insulated pipes to the manifold and room to allow isolation valves and a volumiser (that really is a word that should be confined to hair product adverts!) so that if the ‘above dew point’ approach isn’t enough we can reconfigure without ripping out walls.  
 

So, no immediate need but a bit of bet hedging.

[G and J]

Just now, G and J said:

I don’t know the answers to those questions.

 

So I’m going to try to allow for all eventualities where I can without wasting tons of money.

 

I’m putting a Fancoil into our bedroom, with a drain and also insulated pipes to the manifold and room to allow isolation valves and a volumiser (that really is a word that should be confined to hair product adverts!) so that if the ‘above dew point’ approach isn’t enough we can reconfigure without ripping out walls.  
 

So, no immediate need but a bit of bet hedging.

But I agree with you re the comfopost.  Feels to me like a bit of kit that sounds brill on the tick list and can bump up the invoice for a disreputable outfit but actually delivers little benefit to most houses.   Interesting that the companies I’m talking to re MVHR kit have both strongly suggested not to bother with one, so full marks to each of them.

[Ommm]

1 hour ago, NCXo82ike said:

So all of this has confirmed for me that a comfopost isn't worth it for us.

 

If you're running fancoils on the same loop as UFH, presumably that gives plenty of circulating volume. It would then run offset above the dew point, accepting achieving less than maximal cooling/heating output from the fan coils.

 

It seems to me there's little point in running insulated pipe to supply the fan coils?

 

And is there any need then to provide a condensate drain for the fan coils?

Does this avoiding the dew point idea actually work? 

 

A fan coil has a certain difference between water and air temp. Typically ASHP are rated at 7C. Let's say your room temp is 30C. That's deltaT of 23C.

 

At 80% RH the dew point is 26.2C, so now your achievable deltaT is 3.8C.

 

Assuming a constant heat exchanger area, you need to push 6x as much water per hour and run the fan 6x faster to get the same cooling effect.

 

(Different numbers for different temps/RH)

 

Obviously you can oversize (if you have cooling UFH that's roughly what you're doing). But if the UFH isn't in action a fixed FCU can only go so big, and if the UFH is then the FCU isn't adding very much.

 

It seems quite inefficient to run it that way, especially compared with refrigerant based A/C, where the phase change in the evaporator can absorb a lot of heat. Seems like water is already at a disadvantage and hobbling it further is not going to help.

Edited September 22 by Ommm

[JohnMo]

2 hours ago, Ommm said:

Let's say your room temp is 30C. That's deltaT of 23C.

At 80% RH the dew point is 26.2C, so now your achievable deltaT is 3.8C.

Not sure how good your figure are, but doesn't relate to my house at all. 

 

Same as heating, you do cooling slowly, it keeps the house temperature down and the RH down. I run a target flow of 14.5 and Don get any issues 

 

2 hours ago, Ommm said:

But if the UFH isn't in action a fixed FCU can only go so big, and if the UFH is then the FCU isn't adding very much.

If you run a buffer you really the UFH engaged to provide that function. The floor doesn't need to be many degs below target room temp to get quite a cooling effect.

[NCXo82ike]

8 hours ago, Ommm said:

Does this avoiding the dew point idea actually work? 

 

A fan coil has a certain difference between water and air temp. Typically ASHP are rated at 7C. Let's say your room temp is 30C. That's deltaT of 23C.

 

At 80% RH the dew point is 26.2C, so now your achievable deltaT is 3.8C.

 

Assuming a constant heat exchanger area, you need to push 6x as much water per hour and run the fan 6x faster to get the same cooling effect.

 

(Different numbers for different temps/RH)

 

Obviously you can oversize (if you have cooling UFH that's roughly what you're doing). But if the UFH isn't in action a fixed FCU can only go so big, and if the UFH is then the FCU isn't adding very much.

 

It seems quite inefficient to run it that way, especially compared with refrigerant based A/C, where the phase change in the evaporator can absorb a lot of heat. Seems like water is already at a disadvantage and hobbling it further is not going to help.

I'd see the ability from fancoils added to UFH to preferentially cool certain rooms (e.g bedrooms) handy.

 

Without UFH too, I'd go below the dew point using insulated pipe and condensate drains. 

 

With the UFH, taking the fan coils below dew point would I think require two loops, a diverter, and a volumiser for the fan coils loop?

 

Unless you can run one coming loop at 7 degrees C supplied in insulated pipe, then blend the UFH to a temperature above dew point?

 

I can see the argument for just adding AC, but as additional outdoor unit wouldn't suit our property (mid-terrace).

[joth]

On 22/09/2024 at 16:49, JohnMo said:

Not sure how good your figure are, but doesn't relate to my house at all. 

 

Same as heating, you do cooling slowly, it keeps the house temperature down and the RH down. I run a target flow of 14.5 and Don get any issues 

 

If you run a buffer you really the UFH engaged to provide that function. The floor doesn't need to be many degs below target room temp to get quite a cooling effect.

Reflects my experience. Originally I ran the FCU on its own, to "blast" the bedroom cold before bedtime. This had to be below dewpoint flow temp (below 7) to minimise the ASHP short cycling. But it still did a bit.

I then added the volumizer in series with it, and programmed Loxone to run as much ufh loops as it can (ie in all rooms except any that are too cold) and for a longer runtime, and it doesn't have to be below dewpoint. But, I've insulated everything that needed it so I can run it extra cold if necessary (in a heat wave, and it's not been running for some random reason). But still I prefer not to run it cold as even with all the insulation I find random corrosion on the pump case bolts, the water diverter, etc. basically all the standard UK wet heating ancillary components aren't designed to handle condensation.

 

[Ommm]

On 22/09/2024 at 15:49, JohnMo said:

Not sure how good your figure are, but doesn't relate to my house at all. 

 

Same as heating, you do cooling slowly, it keeps the house temperature down and the RH down. I run a target flow of 14.5 and Don get any issues

 

If you run a buffer you really the UFH engaged to provide that function. The floor doesn't need to be many degs below target room temp to get quite a cooling effect.

 

If you have UFH then you have a massive emitter right there, so worries about cooling area don't really matter.

If you have only FCUs (the point of this thread), then you have a limited cooling area.  Typically they are much smaller than the kinds of radiators you might install for heating with an ASHP.  To follow the 'low temp heating' with a 'high temp cooling' analogy, a smaller radiator with a lower deltaT means you need to ramp up the water flow and extra airflow means more noise to contend with.  Maybe that noise is ok, it depends.  It's not silent like radiators or UFH.

 

The other problem is that during heating your extraneous heat sources (people, solar gain, cooking, electrical equipment) reduce your heating demand, but during cooling those things still exist and serve to increase your cooling demand.

 

My point was that in humid conditions the dew point temp is high and your cooling ability without condensation is limited.  That is typically when you need cooling most, and yet you can't run anything cold for fear of condensation.  Also that folks say that a major comfort of A/C is in reducing the humidity levels, which is something you can't do without condensation collection (as you cool the air the RH will go up, until such time as it condenses).

 

I'm sure there's a system design where it makes sense - I don't have a good handle on the numbers here.  But I think it's going to be harder than heating.

[JohnMo]

17 minutes ago, Ommm said:

 

My point was that in humid conditions the dew point temp is high and your cooling ability without condensation is limited. 

But the point really is you don't wait until the house is up to 30 degs before, you say let's switch on the cooling, like heating it's better to keep things at a even temperature. The house then sits at say 23-25, not in the 30s. 

 

Example, 2 August for us, had an external humidity of 74% in the afternoon, we get all our heat from solar gain, left unchecked the garden room (fan coil) will easily exceed 30 degs. Cooling was left to run on weather compensation. Max temp reached in room was 23 and max humidity was 52%. So dew point was 12.6 degs. If I left the temp to rise to 30 and humidity remained at 52% the dew point jumps up to 19.1 degs so you have condensation issues.