Which ASHP are set up to cool

[Dan F]

1 hour ago, yngndrw said:

We have it all piped up with a mid-position valve to switch between cooling and heating

 

I'm struggling to visualize what your setup looks like.  Why do you need valves to switch from cooling to heating? Aren't you using a single Vaillant circuit for fan coils?  Don't the fan coils need to run for both heating and cooling?

 

 

 

 

[yngndrw]

22 hours ago, Dan F said:

 

I'm struggling to visualize what your setup looks like.  Why do you need valves to switch from cooling to heating? Aren't you using a single Vaillant circuit for fan coils?  Don't the fan coils need to run for both heating and cooling?

 

 

The flow from the heat pump goes into a DHW priority diverter valve, then from the heating side of that into the heating/cooling mid-position valve. The heating side goes off to the radiators (Will be upgraded to underfloor heating after some building work) and the cooling side goes to the fan coil units.

 

The reason that the heating and cooling is separate is due to condensation. The fan coil units are proper cooling ones with drain pans, so they can be run at a low temperature and remove some moisture from the air. Initially we were just going to use a diverter valve but we changed to a mid-position valve at the last minute so that we could use both the radiators/underfloor and the fan coil units for heating in order to boost efficiency. Right now the fan coils are not yet installed - That's a job for over Christmas.

[Dan F]

OK, kinda makes a bit more sense now.  But I don't understand the motivation for doing this vs. using two separate Vaillant circuits and letting Vaillant control everything.  Using two circuits gives you the flexibility to run each zone with its own controller, schedule, heat curve and flow temperature etc.  Any specific motivation for trying to make one circuit service two circuits?

 

On a separate note, do you have a buffer planned?

[yngndrw]

I'm not sure how that would work with two separate circuits, the heat pump can only serve one at a time (heating or cooling) so we are really just diverting. Our installer had never done cooling before so the cooling side was an experiment - It's essentially just a standard weather compensated heat pump setup with the cooling tacked on at the hip. We did try to minimise the amount of primary flow pipe before the heating/cooling mid-position valve in order to reduce the amount of pipe which would be susceptible to condensation.

 

No buffer or hydraulic separation, we do have a volumiser on the return though.

 

I can take a picture of the pipework this evening for better context.

Edited November 21, 2023 by yngndrw

[yngndrw]

Pictures as promised:

 

 

On the wider picture, flow and return from / to the heat pump in the bottom right.

 

The blue diverter valve is for the DHW priority - Down goes to the cylinder. (It goes to the built-in coil and then onwards to a separate DHW charging plate heat exchanger)

 

Above that diverter is the heating/cooling mid-position valve - Right is the cooling pipe which goes upstairs, left is the heating and goes both up and down.

 

The volumiser is on the heating return behind the wall, under the stairs.

 

A lot to fit into a tiny cupboard! Hope that helps to explain the context.

[Dan F]

> I'm not sure how that would work with two separate circuits,

 

Two circuits mean that:

- Everything can be controlled from Vaillant, no need for anything manual outside of Vaillant.

- You can have two zones, with different target room temperatures.
 (this makes a lot of sense if, for example, you have radiators on the ground floor and fan coils on the first floor)

- If required, you can have different heat curves and flow temperatures for each circuit too.

 

If your radiators and fan coils are in the same rooms and you plan to use radiators for heating only and fan coils for cooling only, then I can see how your approach works and may be simpler.

 

In our case, we have two circuits/zones; one for ground floor UFH (heating+cooling) and one for first floor MVHR post-heater (also heating+cooling).  Each zone has its own controller (given it's two different areas in the house).

Edited November 22, 2023 by Dan F

[yngndrw]

Oh I see, sorry when I mentioned manually enabling cooling I mean from within the Vaillant SensoComfort controls, not from something external.

 

We don't have any zones, it's all on pure weather compensation with a steady-state curve - Room influence is fully disabled. (Except for a timed 18C setback temperature overnight) The property is one large zone. (It's an annexe so it's basically and upstairs and a downstairs room.) We didn't want any sub-zoning on the heating to maximise efficiency. (Typical Heat Geek setup basically)

 

Pure weather compensation is working extremely well for the property, upstairs and downstairs are both very comfortable holding a constant 21-21.5C with a COP of 4.5 over the past month - Far better than expected without the underfloor heating. The curve is currently set to 0.5. It's worth noting that we only have the heat pump interface, we don't have the expansion unit so we only have those two MA1 and MA2 outputs - Was really hoping to be able to do it with just that unit.

 

As I say it's all open-plan, so the idea is to put one fan coil downstairs in the kitchen (Supply duct will pull from the hallway so that it doesn't just pull greasy air through the fins) and the other will be upstairs in the bedroom. That should cover the entire property pretty well.

 

 

So with that in mind, we want to retain a single zone across the property. I can see where the manual cooling mode option is in the Vaillant controls although haven't been able to test that because of the outside temperature limit they've set for some reason, the only thing we seem to be missing is the way to tell it that MA1 should be treated as a cooling zone output - I don't know if that should just automatically work?

 

 

This is a diagram of the wiring - The heating/cooling mid-position valve is actually plumbed backwards to what you might normally expect, the A port goes to the fan coil units and the B port goes to the radiators:

heat-pump-wiring.drawio.pdf

 

Truth tables for the mid-position valve, this is how we have a switch controlling the two modes:

 

If the white wire is connected to a permanent live and grey is connected to the cooling signal from the Heat Pump Interface:

White | Grey | Output
 On   | Off  | Fan Coil Unit + Radiators (Heating)
 On   | On   | Fan Coil Unit             (Cooling)

 

If the white wire is also connected to the cooling signal from the Heat Pump Interface:

Grey & White | Output
 Off         | Radiators     (Heating)
 On          | Fan Coil Unit (Cooling)