UPDATED: Air Source Heat Pumps/Air Con - Full Info & Guide, is it cheaper to run than mains gas?

[Deleted User]

grahamc2003 wrote: »

Question on the ecodan. Is the output from the outside unit hot water, or hot refrigerant?

If it's hot water, does it go through a valve to route the water between the rads and HW tank, or does it all go into the HW tanks and a secondary circuit takes the heat from the tank to the rads?

Would the heat losses from the outside unit to a tank 25m away be within spec?

Anyone any experience of Dimplex HPs? Seem to be well thought and offered alongside ecodans - the advantages (so they say) is that Dimplex are UK designed for the UK climate. They have mega kW heating elements which I'm keen to avoid (I assume the ecodan doesn't?)

Thanks.

With the Ecodan it is hot water from the outside unit. Our Ecodan certainly does not have an element to boost to the heating side of things but it does have the capability as there is a DIP switch on its circuit board to tell it if has one or not. Not sure if the Dimplex is the same... Ecodan also built in the UK for our climate.

TiredGeek

Yep, as Jeepjunkie say's, the Ecodan is a monobloc design and heats the water inside the outdoor unit.
Flow and return pipes go to the unit and indoors you have a zone valve which sends water either to the cylinder or to your rads/underfloor. If it's going to the cylinder the Ecodan heats it to ~58'c, if it's to your rads it's set for more like 45-50' (adjustable settings and weather compensating).

Would the heat losses from the outside unit to a tank 25m away be within spec?
Do you mean the outdoor unit is a long way from the house and most of the pipe is outdoors, or the tank is a long way from where the pipes come indoors....
I wouldn't think either is a problem as long as the pipes are really well insulated.

John_Pierpoint

Surely the point is that as the difference between the inside temperature and the outside temperature drops, especially when the external temperature gets near to freezing, and the heat pump turns into an ice making machine, the efficiency in terms of COP (or percentage efficiency if you prefer) DROPS.
This is nothing to do with clever design of individual heat pumps it is a simple case of the laws of thermodynamics.

So for (let us say) 21 days per year, the pump is inadequate.
The solution has three possibilities:
Reduce the area of the home kept above comfort level.
Install an oversized heat pump at a cost of £000s.
Use a secondary source of heating - be it night storage electricity, peak price electricity, a log burner, .............

Probably a combination of all three options.

Obviously every house is different in terms of thermal performance, though a home with thermal mass helps iron out the peaks and troughs, though it can take a frustratingly long time to heat up if allowed to chill during the winter.

grahamc2003

John_Pierpoint wrote: »

Surely the point is that as the difference between the inside temperature and the outside temperature drops, especially when the external temperature gets near to freezing, and the heat pump turns into an ice making machine, the efficiency in terms of COP (or percentage efficiency if you prefer) DROPS.
This is nothing to do with clever design of individual heat pumps it is a simple case of the laws of thermodynamics.

So for (let us say) 21 days per year, the pump is inadequate.
The solution has three possibilities:
Reduce the area of the home kept above comfort level.
Install an oversized heat pump at a cost of £000s.
Use a secondary source of heating - be it night storage electricity, peak price electricity, a log burner, .............

Probably a combination of all three options.

Obviously every house is different in terms of thermal performance, though a home with thermal mass helps iron out the peaks and troughs, though it can take a frustratingly long time to heat up if allowed to chill during the winter.

One characteristic of all HPs is that as the ambient temperatuyre drops, the cop does to. Alternativey, as it rise, the cop rises - and if it's 10C outside, I expect the cop rises to amazing levels, especially if you want warm water circulating (the cop also drops with rising water flow temperatures, so the lower the better).

But within those characteristics, the HP design - and setup/quality of installation - can also have large effects - hence why the quoted cop varies between manufacturers and models.

Icing is the big achillees heel imv. I'd keep rain and snow off mine, but there's still condensatation (or more likely ice deposition) from the air to deal with. I expect the defrost strategy is a really big energy user, so is critical .... and yet almost impossible to get any information on. Like the ambient temps at which it kicks in, or is it via ice sensors on the coils, or ambient humidity levels. I'd like to see the design logic from various manufaturers.

I don't want automatic 8kW heating elements at all - I expect these things are so 'intelligent' you never know when they'd kick in, and it's even feasable they'd kick in even when disabled .. if the HP itself is in danger for example. So I'd do as you suggest, and either rely on the HP itself without electric elements, or, if the situation was that the cop was below say 2 anyhow, turn the thing off and light my stove. Similarly if the defrost is operating more than every couple of hours say, or if theres lots of ice on the evaporator.

But then it comes to statistics. How many hours/days would the weather be such that I'd turn the thing off (due to low cop, icing, too many defrost cycles etc). It would be a sort of manual bi-valent system.

albyota

Hi grahamc2003, there are some limitations when installing a unit 25 metres away, obviously heatloss, but flow rates and pump size also have to be considered, IMO, you would be hard pressed to calculate the running cost difference between a Mitsubishi Ecodan at 25M and a Panasonic or Daikin Split system with or without electric backup.

As for the defrost cycles of most decent heat pumps occurring between about 3 degrees down to minus 5 damp and cold ambient, as air tends to be dryer below minus 5, by reversing the flow of hot refrigerant around the coil, usually five minute cycle once per hour.

TiredGeek

I think the backup elements can be disabled simply by putting a switch (of the correct rating, like a cooker switch) in line with them - if you don't want them to come on - turn them off

Albyota will be able to say for sure but from what I've read they're only used to heat the water if the heat pump can't raise it high enough quickly enough, not as some sort of heat pump protection system, so you should be fine disabling them or even never connecting them in the first place

albyota

The Mitsubishi Ecodan does not have an electric element backup, but the FTC 2 controller does have a DIP switch that can enable a volt free set of contacts that you can connect an external backup heater to, via a suitable contactor, this is never used though. This is completely different to the domestic hot water cylinder immersion heater element, which also can be controlled by the FTC 2 controller, but this is for thermal disinfection (legionella protection) once a week to heat the cylinder to 60 degrees for 1 hour.

Panasonic Aquarea does have electric boost element to help raise the heating circuit water for 20 minutes from startup, or if it can't reach set point within 20 minutes.....and when in defrosting mode.

Not sure about the Dimplex kit, but I'd imagine electric elements are used.

[Deleted User]

I'm sure our ASHP has had to deal with icing but TBH if it has i've never noticed. Temp in house is always stable and running costs massively cheaper than the LPG system it replaced. Probably in the region of £1500 a year cheaper!

Having spoke to a chap who kept his oil boiler following a Daikin ASHP install a few years ago the oil level has never changed in all that time...

In fact the colder the temp the hotter the air coming out of the fan coils as the heat curve does its thing. In theory the ASHP will produce less heat in very cold sub zero temps but if sized correctly this is in our experience has never been a issue.

Plus like us if you have log burners you will never be cold and be much much better off

albyota

Ha ha grahamc2003, believe it or not the Dimplex Aqua-eau is actually made by Panasonic,

http://www.dimplex.co.uk/products/renewable_solutions/heat_pump_air_source/domestic/air_eau/features.htm

http://www.panasonic.co.uk/html/en_GB/Products/Aquarea%3A+Heating+and+hot+water+solution/Introduction/Aquarea+-+New+line-up/10030059/index.html#anker_10030059

nande2000

Well ive bitten the bullet and had an Ecodan 8.5kw installed.
Power usage and heat output seem ok so far (still a bit of air in the rads, but thats getting sorted).

Only concern is the noise output; anyone had the same issue, found a solution ? Or is it something you have to learn to live with ?

In fairness the oil boiler it replaced was a lot louder, but the ashp is more of a low level annoying noise.