ASHP vs Electric central heating system

spudofcongeith

any thoughts on the two systems as a central heating system for our new build 1.5 storey detached house with underfloor heating downstairs (upstairs will be radiators but not being developed until we have more money!), and solar panels and obviously high levels of insulation.

cheers!

Cardew

Welcome to the forum.


It seems a little strange that your new built home hasn't been designed with an integrated heating system.


What is your present electrical CH system? i.e. are you on an Economy 7 tariff with a heat store(a big Hot Water tank)


Is the underfloor heating simply electrical elements, or hot water pipes?


If the latter, the problem is that your underfloor heating will probably not be suitable for an ASHP as the water from an ASHP should be 30C to 35C for maximum efficiency; and conventional hot water CH systems run at much higher water temperatures.


More information please.

Smiley_Dan

If the latter, the problem is that your underfloor heating will probably not be suitable for an ASHP as the water from an ASHP should be 30C to 35C for maximum efficiency; and conventional hot water CH systems run at much higher water temperatures.

Depends on the floor. It's new build, so I assume solid floors with lots of insulation, in which case that temp is probably fine. That's the ideal heat pump heat distribution system, in fact.

I'd be more concerned about ASHP's ability in the colder months.

spudofcongeith

thanks for your replies. i was under the impression that ASHP would work well with underfloor heating as opposed to something like oil CH as its works at a lower tempreture? yes lots insulation. if its an electrical system then still to decide if wet system or not.
Cardew, our present CH system is a static caravan!!
i have an (stupid) issue with oil CH systems - lived in houses with them all my life but would like to move away from them. GSHP not feasible which is what we really wanted and not on mains gas but our concern with ASHP is our sometimes cold winters (in scotland) and therefore its efficiency.
we are also putting in wood burning stove as wood source not an issue.
our architect mentioned the potential of electrical system especially if run inconjunction with solar panels.

cheers

TiredGeek

You'll have to sit down and do some very carefull calculations with regard to price and savings of the systems.

A pure electrical system will only ever give you 100% efficiency, 1kWh of energy in = 1kWh of heat out.
An ASHP will give you about 200% overall for the full year (or up to 400% if you're lucky) but may well cost significantly more to buy and fit. You also have the minefield of getting a GOOD company who know exactly what they're doing and won't c**k it all up - harder than it seems apparently!
So you'll have to work out if the ASHP will pay for itself over the pure electric system and just how long that'll take, then decide if it's worth it to you.

Some ASHP, I'm thinking 14kw Mitsubishi EcoDan, will happily work as low as -25'c, but what the efficiency is like at that temp I have no idea
Our house is in the coldest part of Scotland, they work there for us so fitted right they'll work for you.

Cardew

There is no doubt that an ASHP being installed into a house under construction is far better than a retro install; especially with Under Floor Heating.(UFH)


You might even consider an Air to Air ASHP with ducting into rooms.


As said earlier, if the UFH pipes have already been laid before you considered an ASHP they will presumably be 'sized' to warm the room adequately with water from a conventional CH system(60C or so). Thus they will be inadequate for water from an ASHP at 30-35C


If you intend to use radiators upstairs they would need to be carefully sized and much bigger than 'normal' for the low water temp from an ASHP.


As money is tight, you might be shocked at the cost of an ASHP installation - however you would need to investigate if RHI(Renewable Heat Initiative) will offset that cost.


The solar panels, in Scotland, will have little influence on your heating demand in winter. You would be better having a device(like an immersun) that diverts any spare generated electricity to an immersion heater in a Hot Water Tank.


If an ASHP is ruled out you can go for a 'wet' system on Economy 7/10 where you heat a large thermal store(a big Hot Water Tank) at off peak rates.


Me? with your wood burners, I would go for Oil CH!!

spudofcongeith

sorry i shouldve stated that the house is not even under way - the site is still a green field. lots if investigative work to do so minimal mistakes are made when the build starts, hopefully!
thanks tiredgeek, that was a worry about its effieciency in freezing weather, and compared to were you are we're a soft southerner lol (D&G).
we've had plenty of quotes from ASHP companies both RHI registered and not and yes they aint cheap! the payback is not as good as other renewables and im not sure in a really well insulated house if the usage would be as the companies are trying to suggest?!
if only we couldve done GSHP, we wouldnt be in this pickle....

Smiley_Dan

If it's new build and you have influence over the building design then you have a great opportunity to design a house of such efficiency that energy costs regardless of fuel costs are greatly reduced. Think maximum insulation, airtight, huge south facing windows etc.

Keep tabs on this thread : http://www.navitron.org.uk/forum/index.php/topic,22660.0.html . it's more focused on environmental concerns then money saving but much of the principles still apply.
.

Cardew

Well I would look carefully at Air to Air with ducting to rooms. The COPs obtained are seriously high these days as they operate at low temperatures.


It is almost the standard way to heat electrically in some parts of the USA - look at some US websites.


The downside of course is how to heat hot water.


Can't see why you feel a GSHP would be the answer!

[Deleted User]

spudofcongeith wrote: »

if only we couldve done GSHP, we wouldnt be in this pickle....

Can't you do bore holes for GSHP?


PS ASHP/GSHP... Both work on the same principles...


Cheers

Robwiz

How you heat your house depends on three things: your lifestyle; your budget and your objectives.

With modern levels of insulation it's no longer necessary to go to the expense of installing radiators/UFH in every room and in truth systems using pipes and water are irrelevent. However, the majority of people haven't realised that yet so if you plan on selling in the next few years it would be wise to install central heating. Then your choice of heat source should be influenced by cost and fit with your lifestyle.

If you planning on staying long term, then you consider a masonry stove for new build. Burning 18kg of wood in the evening will put enough heat into the stove's structure (72 kWh) to keep your house warm for the next 48 hours, releasing it as needed (heat flow out of the stove structure is dependent on the temperature difference to the room so they are self-regulating).

An air to air heat pump (AAHP) is an excellent, efficient alternative. Again, due to the high level of insulation and low heat loss, a single 2 kW heat output mini-split unit should balance the heat loss of your house. It may be worth keeping some old school fan heaters for the few really cold days we sometimes get.

A high COP AAHP draws only 450 watts running flat out, and averages about 250 W – within the winter output of a 4 KWp solar PV installation, so a good solution for winter background heating.

I personally wouldn't touch any RHI eligible product with a barge pole. You will pay inflated purchase prices and installation costs, be exposed on maintenance and risk never seeing the returns that the salesman promised.