Aircon options - which is best?

[Adamantium]

I’ve just cut air con from my build to save money but in the event I have any extra cash this is the first thing on the shopping list to come back.

 

thing is I have no idea how much it should cost and have been told there are different types.

 

module in each room - ugly

 

central unit with ducting to each relevant room and one external heat exchanger - no separate control for each room - or is this wrong?

 

would appreciate some advice and maybe a recommendation of who to use?

[dpmiller]

do you have UFH pipes?

[le-cerveau]

Have you thermally modelled the house to work out your requirement?

 

[Adamantium]

SAP calcs only no, thermal modelling but two south facing children’s bedrooms with much glazing.

 

extra thick external block walls (500mm), but two loft bedrooms too which I suspect will get hot.

 

UFH throughout ground and first concrete floors.

 

 

 

 

[richi]

32 minutes ago, Adamantium said:

UFH throughout ground and first concrete floors.

 

Check out @JSHarris's experience hacking his ASHP to cool as well as heat.

[PeterW]

I would be designing out any use of air con. With a decent MVHR setup you can minimize the need for cooling as long as  you aren’t having very large south facing glazing. We have a full room in roof build facing south and even with no MVHR running and the weather a couple of weeks ago the rooms didn’t get to much above 21c. 

[Adamantium]

I’d prefer not to have it due to cost but also my wife hates it. Can’t stand the breeze and the noise.

 

it would only be for occasional use at night.

 

We will be getting mvhr, I wouldn’t be against getting a cold air heat exchanger added to that.

 

underfloor cooling sounds like a genius idea if ufh is being installed anyway as I imagine there’s no noise or breeze.

[Jeremy Harris]

Underfloor cooling works well, in my experience.  Pretty much any ASHP can be reversed and become a cooler, as they do this normally to defrost when in heating mode.  It may not be well documented, it depends on the model, but I found it very easy to switch ours from heating to cooling.  In cooling mode I have it set for a flow temperature of 12 deg C, which means that in practice the floor temperature never drops below about 18 deg C, which in turns means there's no condensation risk at all.  It's most effective where the floor might otherwise be heated up by sun coming through glazing, as by stopping that area of floor from warming up it prevents heat from the floor being convected into the air in the house.

 

Another fairly simple way to add air cooling, if you are fitting an ASHP, is to fit an inline duct heater/cooler into the main fresh air outlet duct from the MVHR.  This then allows the MVHR to deliver cool air to all the rooms whenever the ASHP is running in cooling mode.  It doesn't shift a great deal of heat, as the MVHR takes a couple of hours or more to change all the air in the house, but will probably remove around 1 to 2 kW of heat at a guess, which may well be enough if the house insulation has a nice long decrement delay.  Decrement delay is more important than U value in many ways, so well worth looking at during the design stage.

 

Duct heater/coolers look like this, and should be easy enough to plumb in:

 

[Adamantium]

Thanks for this.

 

my main concern is that I’ll end up with a Luddite ufc or mvhr installer who won’t have a clue about this stuff.

 

is there such a thing as a specialist who consults in this type of thing when needed?

[Jeremy Harris]

14 minutes ago, Adamantium said:

Thanks for this.

 

my main concern is that I’ll end up with a Luddite ufc or mvhr installer who won’t have a clue about this stuff.

 

is there such a thing as a specialist who consults in this type of thing when needed?

 

Probably not.  It's really not that hard to DIY, though, as along as the installation has provision for isolating any buffer tank when in cooling mode.  I just fitted a motorised ball valve in the flow to the buffer tank, so that tank stays warm when the ASHP is running in cooling mode.  I have two remote control thermostats mounted on the hall wall, one sets the heating temperature the other the cooling temperature.  The heating stat switches the ASHP to heating mode, the cooling stat switches it to cooling mode.  I did need to programme the ASHP with the cooling and heating temperatures, but some delving through the manual showed how to do that fairly easily.  Our ASHP is a Carrier, but badged Glowworm, and is identical to the other ASHPs also made by Carrier that carry badges like Kingspan.  Often UK installers may not be familiar with operating ASHPs in cooling mode, unless they are used to dealing with office type installations.  Our old offices had chilled water passive coolers in the ceilings, basically just like radiators mounted on their side on the ceiling with chilled water running through them, but with condensate trays to collect and drain away condensation from the cooled surfaces.

[Nickfromwales]

@JSHarris

I assume the pipe insulation that is used to retain heat also doubles up to reduce any condensation on the pipework carrying 12oC water ? Is that an issue? 

My knee jerk would be to insulate everything even if just precautionary.   

[PeterW]

2 minutes ago, Nickfromwales said:

@JSHarris

I assume the pipe insulation that is used to retain heat also doubles up to reduce any condensation on the pipework carrying 12oC water ? Is that an issue? 

My knee jerk would be to insulate everything even if just precautionary.   

 

Yep - simple condensation analysis is all that is needed. In most instances you only need 9mm of insulation anyway to prevent it. 

[Jeremy Harris]

As @PeterW says, you do have to insulate the pipes, and make sure any joins in the insulation are well taped up.  I find that we do get a little bit of condensation on the UFH manifold, but not enough to cause any drips, it just mists up slightly, like a mirror in a bathroom.

 

I did think about making a box around the manifold, with a perspex front so that the temperature gauges and flow meters can still be seen, but I don't think it's worth the hassle.  The floor under the manifold is tiled with travertine, and there's a bit of PVC angle bonded to the wall/floor joint to stop any moisture getting to the wall (I did the same behind the kitchen units and around the space that the washing machine slides into), so even if there was the odd drip of condensation it wouldn't do any harm.