A Cool(ing) Concept

[BadgerBodger]

Shoot me down. This works in my head…

 

Back at university when completing a mechanical design module I recall designing an energy efficient solution for cooling using passive chilled beams. 
 

As a concept does using a couple of chilled beams in a central hallway for cooling at high level (8m above ground floor level) with an ASHP and MVHR to encourage circulation of that cool air and subsequent recovery/recirculation… 

 

To reduce the weight applied to the roof structure I’m looking at using PIR to ensure a low u-value but I’m worried about overheating in the upper floor area (which resides in the roof space). They are large areas with high ceilings (3.5m to the apex) and have limited windows apart from the hallway which I’m unsure if the will have a positive or negative impact. 
 

In my minds eye the chilled beam is a novel solution to reduce the risk of running the UFH using cold water and the associated condensation risks. 

[JohnMo]

Your beam idea would work and the cool air would fall naturally.

 

But like UFH heating area is king, to allow low running temperature. So reversing to cooling would the whole ceiling be better thann just a beam, allow you stay away from dew point and save being dripped on.

 

Or just do a fan coil?

 

55 minutes ago, BadgerBodger said:

reduce the risk of running the UFH using cold water and the associated condensation risks

What risk is that, you only need floor a couple of degs lower than ambient to cool. So my floor is about 19.5, well away from dew point. Flow temp goes down to 12.5 Deg (100mm.below the surface) for a few minutes and never see any condensation forming anywhere in the system.

[BadgerBodger]

My worry is in the upper floors where pipework runs in a joisted floor. I’m not sure what the air temp might reach because of the larger space, air tightness and increased insulation but unless I’ve misunderstood, the table below indicates that my current room in roof dew point in summer at 40 % rh and reaches 35 degrees quite regularly, the dew point is just above 19 degrees. 
 

How would I manage the flow temp to ensure it runs above the dew point for the relative RH? 
 

I could probably tolerate a wet floor in the tiled hall. I wouldn’t want soggy ground floor ceilings. 

 

[JohnMo]

6 minutes ago, BadgerBodger said:

How would I manage the flow temp to ensure it runs above the dew point for the relative RH? 

If running pipes through your loft they should be insulated anyway. Pipe insulation is generally closed cell, so pipe isn't affected.

 

We are 50% humidity inside, the area of the UFH manifold is about 20 degs. So the dew point (from you chart) is 9.25 degs. So min flow temp is 3 degs away from there. Floor is a good margin off dew point, no matter what the house temperature. So no issues with UFH. If in doubt insulate pipes (they should be for cooling anyway).

[Nickfromwales]

2 hours ago, JohnMo said:

my floor is about 19.5, well away from dew point. Flow temp goes down to 12.5 Deg (100mm.below the surface) for a few minutes and never see any condensation forming anywhere in the system.

That's a lot lower than I've been setting them, so good to hear that. I've not ventured below 14^oC, and 16 where there's an engineered wooden floor (bonded). All pipework insulated to feck and the clips do not touch the pipe itself, EVER, instead they grab around the outside of the insulation so they can't become cold enough to cause condensation to form on them.

[BadgerBodger]

9 hours ago, Nickfromwales said:

That's a lot lower than I've been setting them, so good to hear that. I've not ventured below 14^oC, and 16 where there's an engineered wooden floor (bonded). All pipework insulated to feck and the clips do not touch the pipe itself, EVER, instead they grab around the outside of the insulation so they can't become cold enough to cause condensation to form on them.

Yes, it’s the upper floor UFH i am most concerned about as opposed to the flow/return to the manifolds. I know everyone says that UFH likely isn’t needed upstairs but because of the high ceilings and general area I’d rather have it and not use it that not have it and want for it! 
 

So here if the surface temp of the floor was say 30 degrees and the RH within the house was 50% the dew point would be around 18.5 degrees meaning the flow temp of the water in the upper floor area would need to be above that because the UFH pipework isn’t insulated. 
 

Or am I missing something? 

[JohnMo]

8 hours ago, Nickfromwales said:

I've not ventured below 14^oC, and 16

I think set point depends on how the ASHP controller handles hysterisis. Plus what temperature it really brings the floor down to.

 

Mine doesn't really run for long generally in the 10 to 15 mins range and then off from 10 mins to 4 or 5 hours. Really depends on what the sun is doing and ambient temperature. This is the last cycle. As you will see (red line) it's not spending any time at a cold temperature. 

Set point will depend on how your ASHP responds, if runs for hours on end, 16 degs may be better set point 

 

Edited Tuesday at 07:13 by JohnMo

[JohnMo]

1 hour ago, BadgerBodger said:

of the floor was say 30 degrees and the RH within the house was 50% the dew pond would be around 18.5 degrees meaning the flow temp of the water in the upper floor area would need to be above that because the UFH pipework isn’t insulated. 
 

Or am I missing something

I would say you are missing something. You treat cooling the same as heating - low and slow. Set it on weather compensation. So it's always ticking away. Then you never ever hit 30 degs. Most the time the house is 20 to 22. If you get loads of solar gain you may get short excursions slightly higher. But you shouldn't be in the 30s.

 

So you are looking at a dew point of 12 or below.

[JohnMo]

9 hours ago, Nickfromwales said:

I've not ventured below 14^oC, and 16

I've just taken a wider view of the ASHP operation so over 24 hrs.

 

The mean flow temperature is 17.9 Deg. So pretty high really.