Fan Coil Units for use with a (cooling) ASHP

[-rick-]

6 minutes ago, Ommm said:

Something I couldn't work out... in the absence of external cooling, would a standard dehumidifier help here?  If the room is a closed system isn't it just putting more heat into it? Or is it that the reduced humidity will reduce the 'feels like' temperature more than the extra heat?

 

It's maybe not the most efficient way to organise things, but only really needed for extended heatwaves. Reducing the humidity will definitely affect how it feels, but also lower the dew point that would allow you to drop the water temp running through the floor without worrying about condensation, so you could get more cooling from that system.

 

6 minutes ago, Ommm said:

I have my fan coil swapped for a radiator set up.  It's ok but not brilliant, room temps about 23 when it's 32 outside, some of which is just from the masonry rather than the fan coil. One thing I hadn't realised is that the pipes run through the loft which is a lot hotter than the house, so my 15C flow is causing sweating at the uninsulated pipe clamps and that's dripping onto the ceiling below... I shall have to repaint, but it's probably still worth it for the cooling.

 

Time to insulate those pipes! Waste of money heating/cooling the loft.

[G and J]

I think it’s my turn to ask a dumb question.  (When one has a talent one should use it!).

 

What’s is the issue with condensation?

 

I get that condensation on a tiled floor would not be good.  I’m not trying to cool the floor that much.

 

I also get that condensation on a concealed pipe would not be good, rotting the timber nearby.

 

We are seeing condensation on our manifold when I run the ASHP  at too cool a flow temp.  (OK there’s another question there but our heat pump is doing odd stuff, appearing unwilling to ‘get out of bed’ for flow temps above f cold, so cooling needs to be in ‘hard’ bursts, but that’s another question).

So we run our heat pump, have a nice coolish slab, get condensation on the manifold, so what?  It’s all stainless and brass and plastic, I can put a towel under it to catch the drips, so where’s the harm short term?

 

One day, I’ll have fitted a fan coil upstairs (having major issues finding a ceiling mounted one), and the heat pump control will be sorted so it does moderate cooling so we’ll avoid condensation that way and I can box in the manifold safe in the knowledge that it’s not dripping.  
 

But for now I need to burst cool the slab as that’s what the heat pump wants to do, so is it ok to accept condensation on an exposed manifold during a heatwave?

[NCXo82ike]

1 hour ago, Ommm said:

Something I couldn't work out... in the absence of external cooling, would a standard dehumidifier help here?  If the room is a closed system isn't it just putting more heat into it? Or is it that the reduced humidity will reduce the 'feels like' temperature more than the extra heat?

 

I have my fan coil swapped for a radiator set up.  It's ok but not brilliant, room temps about 23 when it's 32 outside, some of which is just from the masonry rather than the fan coil. One thing I hadn't realised is that the pipes run through the loft which is a lot hotter than the house, so my 15C flow is causing sweating at the uninsulated pipe clamps and that's dripping onto the ceiling below... I shall have to repaint, but it's probably still worth it for the cooling.

So yes the dehumidifier would increase heat by its power consumption: ~200w. So counter-productive. Quite possibly the decrease in internal RH would allow the floor temp to drop lower and the increase in system performance overall.

 

Looking at Messana who still hydronic systems to rich Californians, the dehumidification is a well advertised component. 

[JohnMo]

19 minutes ago, G and J said:

OK there’s another question there but our heat pump is doing odd stuff, appearing unwilling to ‘get out of bed’ for flow temps above f cold

That is just a set up issue, are you running a fixed flow rate? Hydraulically separated etc. what heat pump?

 

21 minutes ago, G and J said:

nice coolish slab, get condensation on the manifold, so what?  It’s all stainless and brass and plastic, I can put a towel under it to catch the drips, so where’s the harm short term?

That is generally ok short term, but if your heat pumps decides to latch on and over long period can lead to condensation on floor surfaces and lead to slips and falls.

 

 

[-rick-]

23 minutes ago, G and J said:

What’s is the issue with condensation?

 

AFAIK the concern is mainly structural damage caused by damp. But also a concern that a damp area might be make a good home for mould.

 

23 minutes ago, G and J said:

So we run our heat pump, have a nice coolish slab, get condensation on the manifold, so what?  It’s all stainless and brass and plastic, I can put a towel under it to catch the drips, so where’s the harm short term?

Short term none.

 

Long term, maybe there's more condensation that you don't see that will cause damage given enough time.

[Wil]

I’m running everything, rads and UFH, at 18 today and most of the rads are sweating buckets. Where it’s an issue there’s a towel on the floor under the rad.

 

Irritatingly I have a 10kW FCU to put in the loft but it’s sitting in the spare bedroom on my ‘to-do’ list.

 

We’re night purging hard, then sealing up and running as above for these couple of days.

Edited 2 hours ago by Wil

[G and J]

11 minutes ago, JohnMo said:

That is just a set up issue, are you running a fixed flow rate? Hydraulically separated etc. what heat pump?

It is a setup issue and I’ve had some input from Maxa technical and am seeking more.   
 

We have a Maxa heat pump, single zone, UFH only at present, no volumisers or any other unnecessary gubbins.

 

13 minutes ago, JohnMo said:

That is generally ok short term, but if your heat pumps decides to latch on and over long period can lead to condensation on floor surfaces and lead to slips and falls.

 

We won’t be getting into the realms of damp floors.  
But what does “latch on” mean?

[Ommm]

26 minutes ago, -rick- said:

 

It's maybe not the most efficient way to organise things, but only really needed for extended heatwaves. Reducing the humidity will definitely affect how it feels, but also lower the dew point that would allow you to drop the water temp running through the floor without worrying about condensation, so you could get more cooling from that system.

I don't have UFH, only radiators. That means most rooms aren't cooled, only one where I've jury-rigged a fan coil in place of a radiator. So dehumidification doesn't help elsewhere, and it certainly doesn't help the unconditioned spaces where pipe sweat is a problem. (this is a traditional 1960s build)

So the question is really whether dehumidifiers are useful in cooling humans in the absence of other cooling.  From this video it seems not - the latent heat of condensation will be released which is roughly like the COP working against you - eg 300W of electrical energy in releasing 1200W of latent heat. Yes the RH will go down, but the temperature will go up much more.  I'm not clear how humans feel humidity but sweating is the same evaporation cycle, so if everything is perfectly efficient then I suppose the air is 1200W hotter but the humans' sweat causes 900W of cooling, meaning the net 'felt' heating effect is 'only' 300W, but it's still a positive 300W hotter.

 

The latent heat release is beneficial when you're dehumidifying a damp property in the winter, but here it's unhelpful.

 

26 minutes ago, -rick- said:

Time to insulate those pipes! Waste of money heating/cooling the loft.

The pipes are insulated, but the pipe clamps aren't (the pipes were installed and then insulation put around them; I have upgraded the insulation but not re-clamped them.  Some of the clamps are now inaccessible).  For heating that's a relatively small heat loss but it's a problem where any amount of sweat is too much.  The other thing I'm concerned about is moisture soaking into the (nitrile) insulation, so pondering replacing with rockwool or polyethylene foam.  I will likely have to move some portions to a different location to get access, which will mean quite major changes. I was planning those changes anyway so I can run at low temps, but it sounds like they're going to be needed either way.

[JohnMo]

19 minutes ago, G and J said:

setup issue and I’ve had some input from Maxa technical and am seeking more

Start a new thread, include model and size. Mine has moved to hot tub heating duty and I replaced with a smaller heat pump. Do you have the full version of the controller manual? Both R290 and R32 are available online.

[joth]

3 hours ago, NCXo82ike said:

So was Copilot lying to me saying the enthalpy core would drop the internal RH at outdoor temps needing cooling?

 

 

 

Yeah, you are right that if it's lower humidity (and temperature) inside then the enthalpy exchanger should help. I was thinking of the case where it's (much) higher humidity inside than out, but that isn't what we have here today

 

3 hours ago, NCXo82ike said:

Have you considered using a standard dehumidifier?

 

Funny you ask - I was literally looking at options immediately after posting here.  I'd like you that starts (or resumes) operation after main power is cut and restored, so I could easily put it on a relay switch to control only running it when really needed (and ideally, during cheap energy window), but got bogged down as the cheaper units all seem to need a push-button press to start operation, or have their own smart/cloud/app integration that I really don't want.

It's something I may yet do if I find a good option. Good news is connecting continuous drainage is easy in the plant room, so doesn't matter if it only has a small internal condensate pan.

 

In the meantime, I've tweaked around my logic to allow the FCU flow temperature to drop a bit under the dew point if cooling load gets high, and let it drop much below dewpoint if the house starts to overheat. I figure a short(ish) period of condensation on all the pumps and valves is tolerable; it's long term dampness on them all I'm concerned about for causing corrosion and parts to fail.

(In all cases the UFH flow is hard-limited to not go below dew point )

 

[G and J]

1 hour ago, JohnMo said:

Start a new thread, include model and size. Mine has moved to hot tub heating duty and I replaced with a smaller heat pump. Do you have the full version of the controller manual? Both R290 and R32 are available online.

I will do if the technical guys don’t sort it.  We’ll live with a bit of condensation on our manifold for now, and I’ll find time sometime to store the manual.