ALi-B

iTrader: (1)

This maybe telling me to suck eggs (I used to work with air conditioning in an earlier life), but its something that always cropped up in the back of my mind. The issue is many manufacturers (and Greenies, fitters, government, salesmen etc.) will tout this and being one of the most efficient forms of heating aside to ground source heat pumps. Saying that they can dish out somthing like 3kw of heat for every 1kw of electrical power put in (i.e more energy out than put in). I've called BS on this claim for the following reasons:

When you need heat, its cold outside, the colder it is outside, the less latent heat that the outdoor unit can aquire, thus reducing efficiency. Requiring more electrical power to heat the building. Even though manufacturers claim they are efficient down to -15C, I'm still sceptical (reasons why follow).

The pipework to these outdoor units are usually located outside of the building or in the roof space; these are akin to the water pipes on wet central heating. Yes they are inslated with armaflex, but they still radiate heat, of which reduces the installation's efficiency, as some of the heat doesn't go where its needed. The same goes for ducted heating units (which are probably worse).

When its cold outside, its usually damp. A cold outdoor unit will freeze, blocking the fins with ice. This reduces airflow, and thus reduces efficiency. Many units have a defrost mode to remove ice from the outdoor unit. Simply put, it heats the fins of the outdoor unit to melt the ice. This uses electricity, which of course makes it even less efficient.

So my view is, on day like today, its sub zero outside, the outdoor unit is covered in snow, the fins are blocked with ice, and it needs to go into defrost mode every few hours. Is it "really" that more effiecient than just having an electrical heater in the room?

My point is, you can get a government grant and concessions to fits these things (for commercial use too, that why I fitted ours - Under ECA, the government gave us the tax back). Yet the reality is, its not really that much better than a fan heater. Or is it? I say this whilst looking at our works electricity bill for this quarter compared to last years when we had oil-filled radiators (next quarter will be interesting, as it'll include this current cold spell).

Thoughts? Yes they are efficient, but in my view only in perfect weather conditions (mild and dry outside) and with a perfect installation (minimal loss from pipes or ductwork).

What do you think?

boomer

We use reverse air-con at work to heat the office, and you do notice a difference on very cold days (such as last week) - it seems to take longer for them to get up to full strength.

Every so often they seem to pause, which i guess is the de-ice thingy you mentioned.

Can't compare efficiencies with other stuff, 'cos they were installed as we moved in, but other benefits include quick heat (as compared with, say, cheaper storage heaters), cooling in summer, de-humidifying, high wall mounting so no loss of office space etc. - so don't base any decisions purely on cost per watt.

FWIW, the power rating for the unit above me is 1750 watts with 5210 watts heat output.

I might pop out and look at the external unit later to see whether it is frozen up

mb

Account deleted by request

I think air source heat pumps and there supposed saving are a myth. In practice I am yet to see them achieve what either the manufacturers/salesmen/suppliers say they will.

I was quoted for a mitsubishi unit and the figures given were at source ie. the unit not at output ie the house. So the loss of power from source to output is considerable.

For me by the time you factor in the cost of buying the unit compared to a standard boiler there are no savings.

IMO of course.

Chop

ALi-B

iTrader: (1)

Yeah, I only really brought up the subject as the ones we have are having a bit of a struggle -with us enduring cold feet and warm heads (solved as of this week thanks to some low power tube heaters behind the desks), and then they go on a tea break every so often, during which I notice the outdoor units steaming away whilst they de-ice. Then I think, thats my electic out there doing that, it should be in here heating the room, not de-icing the outdoor units.

It was still a much needed investment though; All we had before was oil rads. And we now have air conditioning in the summer Just I don't think its efficiency is all its cracked up to be. :

Account deleted by request

They have benefits it is just that they don't perform anywhere near what they say.

I'm using these at the moment http://www.nibe.co.uk/NIBE-Heat-Pump.../FIGHTER-360P/ they quote similar savings to air source by using heat recovery. I doubt very much that they will achieve this.

The whole green energy business is in its infancy really and it is easy for the manufacturers to make promises, time will tell if they deliver on them. Its interesting that 5 years ago everyone was fitting solar or PV panels. Now most people in the know have found out they dont perform in our climate and when factoring in the cost of buying against saving it takes 15/20 years to make the investment back. I would also take a bet that not many units will still be working in 15 years!!!

I should add for people who have no gas it should pay back quicker purely due to the cost of oil. Time will tell whether heat recovery or air source are the best solution cost wise.

Cheers, Chop.

Account deleted by request

Forgot to add, Mitsubishi told me that the unit would work as low as -7 but I just cant see that possible!

Chop

scud8

iTrader: (1)

The air conditioning units in my conservatory have been as much use as a chocolate teapot over the last three weeks, so either there isn't enough heat outside for them to recover or they're broken. I'm pretty sure they're not broken as there was a brief period between Xmas and New Year where they did heat the room.

Power Junkie

iTrader: (1)

I have an 11kw air source heat pump and it has been working very well even at -17 that we have had up here. As for the running cost it is a hell of alot better than a normal electric system and will still work out cheaper than oil.

boomer

That is still 266 degrees kelvin above sero!!

i.e. There is still energy (heat) out there, it is just a steeper slope to push it up. I guess the limiting factor is the temperature that the refrigerant freezes at, but efficiency falls depending on the temperature differential.

Thinking about it, last week (minus 8 celsigrades) means that the refrigerant has to be warmed up by around thirty degrees to warm the office - hence the delay getting up to full strength.

Looking at the outdoor units today, they did have ice on some of the fins, but no sign of any steam

Ironically, the unit in our computer room is still in "cooling" mode!!

mb

Power Junkie

iTrader: (1)

The ASHP we have is very quiet, we never really notice it. the wind in the trees makes much more noise, if your looking at a GSHP you will need alot of easy to dig ground, I did look into it but we dont have enough soil before bed rock so not an option.

boomer

You can get vertical GSHPs which drill down 300 or more feet into the ground, so you don't need a lot of land or deep soil!

mb

Power Junkie

iTrader: (1)

looked into that too, but would be very expensive at a few Łk per hole, so the ASHP got our vote.