Top up heat sources

[EverHopefull]

Hi I am currently at the purchased land stage of a build and just starting secondary talks with architects, so just getting started I guess.

I read through the many articles on this and other forums and have jumped in with both feet and signed up to this one as it feels honest and varied enough for most outcomes of build choices.

I have a simple question to kick off with and that is "Has anyone here ever used/considered using a traditional split aircon unit with heating capability as a "top up" heating source for a highly insulated new build". I have not seen anything on my ride around the internet so far but as heat pumps are being touted as a great core heating source it seems odd that the smaller devices that have been around for many years and presumably having a great COP spec have been largely ignored. They are instant and do not punch great holes in the air tight envelope of a building and would on the face of it, appear a great solution to what I read is a fairly regular issue with supplementary space heating?

Interested to hear your thoughts/experiences as I am at this point considering their use in my build.

[ProDave]

Hi and welcome to the forum. You made a good choice, this is a fantastic place.

 

I think there are 2 issues with an aircon unit. First they tend to be single room, so you would need several of them, and secondly they are usually split systems so you need them gassed on site with the refrigerant gas so no chance of being DIY  installed.

 

Many of us have fitted air source heat pumps and the monoblock type only have water flow, water return and some cables so don't "punch great holes in the air tight envelope"

 

They work best with wet under floor heating, and can be used for cooling if you have a concrete slab or using a "fan coil unit" which blows out cold air in much the same way as an aircon unit.

[EverHopefull]

Cheers Dave.

In my scenario the aircon unit would be quite a small unit that would probably sit in the main open plan lounge/reception area to address the "chill" that maybe some would sort out with a wood burner or similar. The MHRC would then distribute and balance things. It would not be excessive heat required, just localised instant gratification.

I was myself quite keen on the wood burner from an asthetic stance but also now realise that there is overkill in such insulated buildings.

[Dreadnaught]

Welcome @EverHopefull. I have this question too, so will be reading the responses with interest. Thanks for posting.

Edited November 29, 2018 by Dreadnaught

[PeterW]

Welcome !

 

you would be probably better looking at something like the Mr Slim range of units from Mitsubishi as these can be fitted in line with the Lossnay MVHR systems. It would need you to fit something like this so you would need to plan carefully as these units aren’t small ..!

 

There are a number of benefits of ducted AC however they do need insulated ducting throughout so you need to be careful on positioning. A standard split unit would only be useful for a single room - done properly you could comfortably do a whole house. 

[jack]

Welcome to BuildHub.

 

A few thoughts:

 

The UK doesn't have a history of ducted air heated and/or cooling in domestic settings. The concept of using aircon to warm a space just isn't in the consciousness of the general population or domestic electricians/plumbers whose opinions would usually be sought on heating matters. 

 

Subjectively, air heating tends to be considered less pleasant than radiant heating. Heating the air The air is very dry, which some people have physical reactions to. Also, while the air in a room can be heated up quickly, in my experience the room itself still won't feel comfortable until the furniture and walls have warmed up. That's a much longer process than heating the air.

 

I'd be wary of solutions that rely on MVHR distributing heat from one room throughout the rest of the house. It does work to an extent (we used a 1.5kW column heater in the kitchen to warm our entire house last winter), but switching on aircon heating for an hour in one room will have little impact on the temperature in the rest of the house.

 

In my opinion, if you're going to have MVHR anyway, you're better off looking for a solution that introduces some heat into the MVHR supply. Low level heat to all rooms will work a lot better than having one room being blasted, imo. There are all sorts of options for this. If I were doing it again, I'd stick with UFH driven by an ASHP, but add a loop to allow some comfort heating of the MVHR supply air (really just enough to take the chill off the air due to the imperfect heat exchange in the MVHR unit).

[ProDave]

Some mvhr units contain an air to air heat pump, I believe Genvex is one such init mentioned on here from time to time.

[Dreadnaught]

4 minutes ago, jack said:

If I were doing it again, I'd stick with UFH driven by an ASHP, but add a loop to allow some comfort heating of the MVHR supply air (really just enough to take the chill off the air due to the imperfect heat exchange in the MVHR unit).

 

That strikes me as an extremely good solution. Hadn't thought of the extra loop idea.

 

More generally, as I have read, one of the risks relying on duct heating alone is the risk that true duct-heating systems require larger ducts for greater volumes of air. At the coldest extremes and with usual MVHR size ducting designed for slow air flows, forcing heated air around the house through those ducts at the volumes needed can lead to unpleasant noise and whistling in the ducting. It could work for the most highly insulated homes but would need to be carefully judged. Plus the extra cost and implication of insulating the ducting puts me off although others have said elsewhere that it may not always be needed.  @jack's solution, on the other hand, is the best of both worlds. I favour it.

 

[EverHopefull]

Hello Jack,

 

I take your point about the "dryness" of aircon supplied heat and yes it can be very uncomfortable. I guess the MVHR with built in heater is an option.

There does seem to be a very high level of satisfaction with the capability of MVHR combined with UFH with ASHP combinations to provide a background level of heat for the whole house.

I think it boils down to having a source of instant heat that is not overkill in KW to allow for those occasions where temp drop externally and occupants allowing heat to leach out cause an uncomfortable lowering of room temp. I also imagine that if such a perfect device existed it would be a "golden egg" invention.

[Jeremy Harris]

Welcome,

 

We have a Genvex MVHR with a built in air to air heat pump, which is effectively the same as a split air con unit, but with multiple ducted outputs.  It can heat the house with no problem at all, and has a high COP when doing so.  It can also cool the house a bit in summer.

 

We never use the heating function, as we hate the feel of it.  It does dry the air a bit, but I think the main reason we don't like it is just a personal preference for the feel of the UFH.  As a consequence, I've effectively disabled the heating function in the Genvex and just left the cooling function active.

 

 

[ProDave]

My thoughts are MVHR ducts tend to be put in ceilings.  That is a very good place to introduce cool air for cooling, but a very bad place to introduce warm air for heating (which would work much better with near floor level ducts) 

[jack]

13 minutes ago, EverHopefull said:

I think it boils down to having a source of instant heat that is not overkill in KW to allow for those occasions where temp drop externally and occupants allowing heat to leach out cause an uncomfortable lowering of room temp. I also imagine that if such a perfect device existed it would be a "golden egg" invention.

 

With a well-insulated house, sudden drops in external temps don't make any real difference. I have no idea what the temperature is outside unless I look at the weather forecast (or, you know, actually go outside!) 

 

Also, if the warm air is let out for some reason (eg, door left open), it very quickly recovers. That's part of the joy of UFH in a well-insulated house.

[Ed Davies]

Mini-splits are used as the primary heating source in a number of new-build well-insulated houses in North America, particularly in the NE which is a lot colder (though sunnier) than the UK in winter. In the US NE, of course, their ability to cool in the summer is more useful than it is most of the time in the UK. It's something I'd seriously consider for an on-grid UK new build apart from the point that they don't help with domestic hot water which tends to be a significant portion of the heating requirement.

[EverHopefull]

Thanks guys for your input. I knew it was the forum to be joining!

Once I have the architect back on reigns i will see what budget is left for the fabric first approach.

[AliG]

I have often wondered this also.

 

However, I was staying in a hotel last week in North Dakota and at -13 outside the aircon unit was running constantly to keep the room warm and it was very annoying.

 

My granny's old council house had ducted air heating and it wasn't noisy, but if I remember correctly, the outlets were around 400mm square and connected almost directly to the heater.

 

Heating requires a lot more airflow than MVHR. It might be OK with a very well insulated house with low heating requirement, but I think it would be annoyingly noisy in the winter.

 

The nice thing about UFH is that once the slab has warmed up it should keep a pleasantly consistent temperature.

Edited November 29, 2018 by AliG

[EverHopefull]

My only experience of UFH so far is with a 20 year old ScandiaHus. It had a floating solid wood floor which seemed to be very "bouncy" and a heat recovery system that was either badly commissioned or designed that spent most of it's time switched off. It's main feature was to make every obnoxious smell available in every room of the house!

Hoping that these days things have improved greatly with both systems.

[joe90]

Oh yes, read the many threads of people (like myself) who have UFH in a solid slab that acts as a storage heater in that it holds heat well and temps don’t tend to fluctuate (and they don’t bounce!). Also there are many here that have modern MVHR units that work well,  it as you say when commissioned properly (note to self, MVHR balancing on my to do list). My build is recently finished so I am still “tweaking” components to give the best performance but others here have been there, done that and are benefitting greatly.

[Cambs]

I too am reading this thread with interest because I need to start thinking about the heating and cooling solutions for my next self build, due to start in the next couple of months.

 

In my last build (build 10 years ago, so not to anywhere near passive standard) I had UFH downstairs and radiators upstairs, powered by gas boiler, plus MVHR.  We had rooms in roof and it became hot in summer, so we added a number of split aircon units to provide cooling only in the bedrooms.  We occasionally used these to provide spot heating on the odd cold day - I really didn’t like warm air heating.  We had one of the very rare (in the UK) forced air systems in a previous house and it wasn’t very pleasant or easy to get on with.  We’ve spent a fair bit of time in colder climes in North America where warm air systems are common and I didn’t like it there either.

 

For the next build, we have no gas, and will be building to near passive standard, so my current thinking on the solution is to have ASHP plus UFH downstairs.  I wouldn’t have any other form of heating for the main living areas - UFH is excellent there.  For the upstairs, again, we have rooms in roof but the thick Warmcel  insulation should hopefully regulate temperatures better than the previous build.   I was thinking about pairing the UFH downstairs with fan assisted radiators upstairs.  Something like these from Panasonic (other suppliers are available):

 

https://www.aircon.panasonic.eu/GB_en/product/aquarea-air-radiators/

 

With this set up, we can hopefully switch over to cooling the slab in the summer and getting cooling from the air radiators upstairs if needed.  We’ll also hopefully have individual room control upstairs too.

 

All still to be finally decided on though....

 

 

[Jeremy Harris]

@Cambs, we have UFH in the slab downstairs, no heating at all upstairs (except for heated towel rails in the bathrooms) and our house is room-in-roof, with 400mm of warmcel blown in between the deep rafters.  Upstairs doesn't overheat or get too cold, as long as we remember to close the bedroom doors on hot days (to stop heat from rising up from the hall to the bedrooms).  I reverse the ASHP to cool the slab down in hot weather and that works well, plus we can provide a bit of additional cooling via the air-to-air heat pump in the MVHR.  Seems to work very well, and is very comfortable all year around.  I did find that I needed to reduce the solar gain a lot, to stop overheating, though.

[Cambs]

4 minutes ago, JSHarris said:

@Cambs, we have UFH in the slab downstairs, no heating at all upstairs (except for heated towel rails in the bathrooms) and our house is room-in-roof, with 400mm of warmcel blown in between the deep rafters.  Upstairs doesn't overheat or get too cold, as long as we remember to close the bedroom doors on hot days (to stop heat from rising up from the hall to the bedrooms).  I reverse the ASHP to cool the slab down in hot weather and that works well, plus we can provide a bit of additional cooling via the air-to-air heat pump in the MVHR.  Seems to work very well, and is very comfortable all year around.  I did find that I needed to reduce the solar gain a lot, to stop overheating, though.

 

The issues that we might face upstairs are that we have lots of dormers, south facing, with limited opportunity for solar shading.  The plot is in the curtilage of a listed building, in a conservation area and with a set of planners who were split down the middle as to whether or not there should be planning permission granted and it seems all of the ones who voted “yes: for the original application have since moved on ☹️ .  The south facing windows all face into the plot for the listed building.   We basically can’t change much about the outside on the house to introduce some form of shading.  The only possible option might be solar film but sticking an overhang or a brise soleil on the outside would not be acceptable to the planners.  Add to that an other half who likes to be able to tweak bedroom temperatures constantly leads me towards thinking that UFH + Air radiators might be the way to go, if night time purging is insufficient.  I’d like to keep the options open at this stage - I want to avoid and expensive split air con retrofit like I had to do last time around.

[ProDave]

1 hour ago, EverHopefull said:

My only experience of UFH so far is with a 20 year old ScandiaHus. It had a floating solid wood floor which seemed to be very "bouncy" and a heat recovery system that was either badly commissioned or designed that spent most of it's time switched off. It's main feature was to make every obnoxious smell available in every room of the house!

Hoping that these days things have improved greatly with both systems.

That mvhr was either faulty or wrongly installed.

 

There is a misconception that it recirculates air. It does not.  Fresh air is draw in and enters all the "supply" rooms. Stale air is extracted from all the exhaust rooms.  Inside the mvhr the 2 separate air streams pass through a heat exchanger so most of the (otherwise wasted) heat in the exhaust air gets put into the fresh supply air.

 

If you were getting bad smells in the  supply air, the heat exchanger was either faulty or wrongly fitted. 

 

I have ufh in suspended wooden floors and they are not bouncy. Again they were either built wrong or something has failed.

[jack]

2 minutes ago, ProDave said:

If you were getting bad smells in the  supply air, the heat exchanger was either faulty or wrongly fitted. 

 

...or the inlet and outlet are too close together on the outside of the building.

[EverHopefull]

I also discovered that the filters were original items! ?

[jack]

46 minutes ago, EverHopefull said:

I also discovered that the filters were original items! ?

 

[Jeremy Harris]

I've found that our fresh air intake filter gets very dirty after 6 months.  I can get away with cleaning it with a vacuum cleaner maybe once or twice, then I have the fit a new one.