Just told that split system for UFH / fan coil cooling is not possible

[flanagaj]

I just had a conversation with an ASHP installer and he told me that they would not install a system that was used for cooling via UFH / fan coils as it would result in condensation.  I tried to explain that you can actually run two different loops at different temperatures, so your UFH was above dew point and the feed for the fan coils was below dew point and you just insulate the pipework and have condensate drains.

That is correct isn't it?

[JohnMo]

No idea why you keep trying to make stuff complex. Just do it all above dew point. Then no mixer no second set point etc

[JamesPa]

19 minutes ago, JohnMo said:

No idea why you keep trying to make stuff complex. Just do it all above dew point. Then no mixer no second set point etc

I agree with @JohnMo, but installer may still refuse even if you run above dew point because he won't know anything about cooling and wouldn't want the responsibility and you probably haven't paid him to do a design for cooling.

 

So don't tell him, make sure he fits a system that is capable of cooling and which can measure and control to dew point (check specs yourself if necessary), then run above dew point also without telling him.  

 

If you are worried this will invalidate your warranty, which it just might, then you may need to pay for a cooling design!

 

Edited Tuesday at 12:07 by JamesPa

[nod]

I’d three quotes and all said Cooling was pointless 

[flanagaj]

 

1 hour ago, JohnMo said:

No idea why you keep trying to make stuff complex. Just do it all above dew point. Then no mixer no second set point etc

 

But why does adding a mixer make it complicated?  My understanding is that it's simply a case of taking the returned warm water from the fan coil circuit to raise the temperature of the water used to feed the UFH. 

That aside, I think just getting them to fit the ASHP and then I can do the associated cooling parts is probably the best solution here. 

[JamesPa]

50 minutes ago, flanagaj said:

But why does adding a mixer make it complicated? 

It adds little or no value unless there is a very specific reason for it, and it's another component to pay for, go wrong, and complicate any problem diagnosis.  Also complicates weather compensation (are you planning a weather compensated mixer for heating, if not how do you plan to achieve this?)

 

Heat pump still has to produce the higher (or lower in the case of cooling) of the two temperatures, so that defines the efficiency you will get. 

 

What's the added value of running at two temperatures?

 

I agree that getting them to fit the ASHP then doing the associated cooling parts is probably the best solution here

 

Edited Tuesday at 14:06 by JamesPa

[flanagaj]

27 minutes ago, JamesPa said:

What's the added value of running at two temperatures?

I assumed (could be wrong) that if the temperature feed to the fan coils was at a much lower temperature than the dew point temperature, then you will get a much higher degree of active cooling than if you ran the feed temperature above the dew point, like you need to for UFH cooling?

[-rick-]

You would, but the question is do you need that extra cooling? If you don't actually need it to achieve the temperatures you want then it's an over complication to install it.

[JohnMo]

1 hour ago, flanagaj said:

But why does adding a mixer make it complicated?

If your chosen heat pump doesn't have an in-built mixer control you will have to add that, an ESBE valve and actuator aren't cheap either, a third party mixer controller isn't cheap either. Value adding possibly not. So a couple of layers of complexity.

 

So now your flowing at 7 degs, to get max output from fan coils and mixing up to allow UFH, so need a temp above about 13 degs generally. So now just incase you have messed up you need to sense house dew point and make the ASHP do something different in case you start to get humidity issues. Another layer of complexity 

 

Then in winter you need more work arounds to get everything happy again for heating, where I assume you would just run straight WC? And another layer.

1 hour ago, flanagaj said:

My understanding is that it's simply a case of taking the returned warm water from the fan coil circuit to raise the temperature of the water used to feed the UFH. 

Why would you be getting warm water from the fan coil? If your flowing 7 Deg water into fan coils, if they are running full chat you are likely to see a dT of 5. So return water is 12 degs, below dew point. If the fan coil fan is off because room is cooling enough the dT will be very low, so now you could be pumping water well below dew point.

 

KISS.

[JohnMo]

Active cooling allows comfortable rooms at much higher air temperature than you think you need. You simply do not need the room at 20 to be very comfortable.

 

Our lounge is sitting at 23, currently and very comfortable (under floor cooling on) if a little too cool.

 

Our summer house with fan coil is sitting at 22, again well comfortable. Was in it yesterday with full sun on it, it was sitting at 24, again a nice comfortable place to be.

 

[Beelbeebub]

You could wait for (hopefully) the position on grants for air to air systems to change for the better and then just install one of those. 

 

Our UK obsession with A2W systems is based on retro fitting to existing heating systems. 

 

As far as I can see the only 2 advantages A2W systems have is

 

1) *once installed* the emitter side of the system can be worked on by a regular plumber 

 

2) it will retro fit into an existing wwt system *as long as the pipes and emitter are suitible*

 

There is a possible 3rd which is some people prefer the heat given off by a wet system to a blow air system. This is particularly true of UFH. 

 

But if you are using fan coils that 3rd point is moot and even the 2nd point is fairly weak. 

 

Which leaves you with point 1.

 

If you are comfortable with calling in a specialist to do work then that's sort of irrelevant. 

 

Right now not you need to find a specialist plumber to work on A2W anyway,   so not much difference to call an air con guy instead.