With the recent heatwave, along with a lot of people I’ve been looking at various options for cooling. Heatpump will be installed in about 2 months time, and it’s connected to UFH, so I know I’ll be able to use that to mitigate somewhat downstairs temperature if I’m careful in respect of dew points.
what I was reading about was the use a ducted fancoil(s) in our loft space so that there is only a couple of grills in the various bedroom ceilings, and the heat pump providing cooling that way?
has anyone done anything similar? I did see that vaillant offer such products (arovair I think), but only seem to provide links on international websites not uk?
What about the cheapest high capacity aircon unit on the upstairs landing, along with a duct from the far corner of each bedroom with a inline fan to take the air to above the aircon unit?
Efficiency and the best possible comfort is hard to justify for 3 weeks use a year, but such a basic system would give a lot of cooling and lower the indoor dew point. The cooled UFH will radically reduce the heatgain of downstairs rooms.
We have a Vaillant GSHP, which I have enquired to see what it would take to run cool into UFH. I would then want to add cieling ducts to bedrooms as we don’t have any outside wall options for installations.
This is certainly an issue I have been considering. I never felt an ASHP was going to be suitable for me for cooling as I have just radiators and even without originally knowing about the dew point issue I could not see it working.
I am currently leaning towards having a separate multi-split AC system for cooling. However an option that might work for you is an Air-to-Air HP rather than the more common air-to-water HP. Then you can use (air) ducting in the ceilings with ceiling vents.
An apparently unique product you might also want to look at is the following Samsung unit.
Their TDM Plus combines an air-to-water for heating and an air-to-air for cooling in the same outdoor unit.
I currently cool via the floor (UFH) we are have pipes 100mm down in concrete and less than ideal 300mm centres. We are NE Scotland so actually outside temperature is nowhere near what you get down south. But we get loads of solar gain so floor cooling does an excellent job of keeping things comfortable. Biggest advantage is overheat recovery time, and comfort rather than ultimate air temp. I am about to add a fan coil to MVHR. Not really for cooling as they are pants for that but more summer dew point control. Will flow with 14 Deg water and that should knock some water out the air that wouldn’t be done otherwise, hopefully giving a better margin to dew point while cooling.
The following seems to be an average price for the external unit.
For the benefit of everyone, one might feel it should be possible to take the heat extracted via the cooling (air) half to boost heat via the heating (water) half - after all an ordinary ASHP works by taking heat from air and transferring it via water to warm the house. However clearly you would not have room heating and room cooling going at the same time.
What is perhaps less obvious and I believe this unit does not do but should is to take the heat extracted via the cooling half to boost the heat supplied to a hot water tank. You would after all want hot water even on a hot day. Samsung if you are reading this please advise on why this is not done as it would logically boost efficiency.
Was sitting here sweltering having a similar idea, but a trickier starting point.
I’ve got a Vaillant aroTHERM Plus 7kW, rads throughout, and no hydraulic separation — it runs direct, single pump, no buffer or LLH. Cooling isn’t enabled yet. I want the same loft fan coil feeding a couple of bedroom ceiling grilles, just to take the edge off a few hot days.
Fitting a multi-split not an easy option, and I’ve got surplus PV I can’t export due to G99 limit, so midday cooling is basically free energy.
My problem: the heating performs perfectly as it is, and I don’t want to compromise it by dropping a low-loss header into a working direct system. So I’d rather use a changeover valve with the cooling circuit sized to keep the heat pump above its minimum flow (and a buffer only if needed). The question is whether a sensible loft fan coil on warm chilled water (~16–18°C) can actually pass the heat pump’s minimum flow. If yes, a valve does it; if not, I may be forced back to an LLH I’d rather avoid.
So:
Does anyone know the aroTHERM Plus 7kW minimum flow / volume figures?
Has anyone run a fan coil off a monobloc without an LLH and held minimum flow OK?
What cooling output did you get at ~16–18°C flow (not the 7°C headline), and did you parallel units?
As you’re not looking to cool at condensing flow temps, I’d sack off the idea of a centralised, ducted fancoil (expensive & disruptive to install), and just fit off the shelf Jaga Hybrid fan assisted convector radiators in place of your existing rads. They’re readily available, cheap used/new-old-stock, and a straight-ish swap with existing rads.
I’m about to do the same thing; replacing 7x standard steel K2/K3 rads with Jaga Strada units, and adding DIY controllable fan arrays. Calculated cooling power: ~4.3kW at 16/18C flow temps, 27C indoor. To get that kind of cooling power with a single ducted fancoil, at those flow temps, you’d need a frikkin gargantuan unit…
Thanks — that’s a really useful steer, and the capacity point is well made. A single ducted fan coil at 16–18°C flow does need to be big, and distributing the cooling across several emitters clearly gets you far more output at those warm flow temps. Point taken.
The snag for me is the existing pipework, not the emitters (the whole rad system went in only a year ago with the HP). My existing rad feeds are all buried in floors and walls with no practical access, so I couldn’t vapour-seal them — and any chilled pipe running through the fabric uninsulated will condense on the outside and drip into the structure where I’d never see it. So swapping to fan convectors would mean putting chilled water through distribution I can’t insulate, which rules it out for my house as far as I can see.
That’s actually what pushes me back towards the loft fan coil: a new dedicated circuit can be insulated properly as it’s installed. I can run it up the outside wall from the plant location straight into the loft, so there’s no buried internal riser and a fully vapour-sealed run end to end.
So for me it comes down to whether one loft unit (or two in parallel?) can deliver enough at 16–18°C flow while still passing the heat pump’s minimum flow. Your ~4.3kW across seven Jagas really highlights the challenge of doing it centrally — that’s the number I need to understand.
Good luck with the Strada conversion — I’d be genuinely interested to hear how the DIY fan arrays and condensate handling work out in practice.
I don’t believe you’ll need to insulate/vapour-seal any pipework if you’re running flow temps above the dew point (which your mention of 16/18C would indicate).
I’ve been running our 7kW Vaillant ASHP in cooling mode for several weeks now; our pipework is insulated, but not vapour sealed, so I’m erring on the side of caution and running above the dew point. The Vaillant Sensocomfort controller has functional dew point monitoring built in; I’ve set ours to 2K above condensing. No drips as of yet, works pretty well.
I also considered installing a separate circuit for cooling for much the same reasons as you’ve mentioned, but sense got the better of me. Running the ASHP above dew point has kept our house at 24-25C during the last two severe heatwaves, with just fans fitted to a couple of standard steel rads and a floor standing fan running in the kitchen to stir the cool air that the UFH produces in there. With the Jagas, the cooling power should be multiplied several fold…
That’s really helpful — reassuring to hear it working on the same 7kW unit, and the 2K dew-point setting is exactly the detail I was missing, thanks.
One thing decides my whole approach though: my rad feeds are buried in floors with no insulation and no access, so unlike yours they’d effectively be bare. Two questions:
Have you run it through any warm humid weather yet, or mostly dry heat? I’m wary of a muggy spell pushing the dew point up.
Would you trust bare pipe on the same 2K margin, or do you think your insulation is doing more work than it seems? Any condensation on my hidden runs I’d never spot until it’s a problem.
If bare unseen pipe is genuinely safe, the simpler Jaga swap reopens for me and I can forget the loft circuit. If not, the new insulated circuit still looks the safer bet. Appreciate the steer.
Fair point - I’d got stuck on the dew point limit from thinking about the rad option and hadn’t reconsidered it for a sealed new circuit. With a proper condensate tray and drain on the fan coil there’s no reason not to go cold, and at 6-7C the output problem largely goes away. Gets me some dehumidification too.
Just means the insulation has to be spot on everywhere, and the condensate drain will actually be doing some work - so gravity fall rather than a pump if I can manage it in the loft.
Thanks, that simplifies the sizing considerably.
I can only talk from experience: running our system with dew point monitoring enabled and an offset of 2K has worked really well throughout the last two heatwaves. No condensation issues, and huge boost in comfort with the addition of a floorstanding fan blowing across the UFH in the kitchen, and fan arrays on a couple of K3/K2 rads in bedrooms.
Not got as far as looking at actual units yet - at the moment I’m just trying to work out whether the idea is feasible at all. Your experience with the 2K dewpoint offset through the heatwaves is really useful though, thanks.
Your ducted fan coil can lower dew point, so you could have a mixer/pump (with bypass for heating) to send water above dew point to radiators and water below dewpoint to loft fan coil.