Air Source Heat Pumps... Questions!

[littlespark]

Listening to the radio the other day, and UK govt has announce no new gas boilers to be sold by 2035 and everyone should go with ASHP... £5k grant to get one..Let me add... only england and wales. We'll stick with peat up here for now.
The following questions.
Probably easy to answer, but just pretend i'm an idiot for 5 minutes


They work by extracting any residual heat in the open air, compressing it and using it to heat the home.... so why are they outside and not inside, extracting already warmed air?

They dont work very well with microbore to radiators. The phone-in callers on the radio said they had to increase the pipe sizes, thus adding to the install costs. Also having to increase the sizes of many of their radiators.

The heat that comes out of these isn't as hot as a traditional boiler... so where do you get hot water? Immersion heater to top-up?

What i saw on a news programme, you get the unit outside... another inside, plus a water tank.. So takes up much more space than a wall mounted combi boiler, that can hide in a kitchen cabinet if need be. Not a lot of one bedroom flats have any space for such equipment.

And discuss.....

 

[Zerax]

Firstly... you need to take what you read/hear about in the media with a pinch of salt... reporters are generally not technical and mis-understand alot of things... I think the plan is to ensure that boilers sold after a certain date can be easily converted to run on Hydrogen as well as Gas.

 

[littlespark]

that should have been the first question;

"is this a load of tosh?"

 

[loz2754]

Think of it like an air conditioner in reverse.
You take heat from where it's not wanted and pump it to where it is wanted. If you had the unit inside the house, it would extract the heat from the warm air to heat up the water tank, making the house cold in the process.

 

[Zerax]

There are different ways to implement 'heat pump' technology... the way you describe is often used in the anti heat pump argument as it's trying to directly replace a gas boiler with an Air Source Heat Pump. The simple fact is... that heat pumps are not a 'one-solution-for-all' thing. Making them work in some properties will be extremely difficult.... but will be very easy to implement in others.

For example... the 1 bedroom flat that you mention would be better served by an air based system, not a traditional wet radiator system... owing to it's small size and low heating need.

My frustration with all these big government ideas is that miss the most obvious change of all.... the building regulations should be amended to ensure that all new properties built from now on... have significantly better insulation and heat pump heating systems. We are still building thousands of very low quality housing... with gas boilers in them !!!

 

[snowhead]

They work by extracting any residual heat in the open air, compressing it and using it to heat the home.... so why are they outside and not inside, extracting already warmed air?

Air source Heat pumps absorb heat from outside air, Ground source from out of the ground, yes even when the ground or outside air are lower than the temperature of the heat or water the units eventually produce, that's the magic of Refrigeration.
Neither source the heat from inside the house, if they did it would be called air conditioning and the house would be cold.

It's not a load of tosh, it works and has been doing so for years and years.
What is tosh is the cost of doing it, nowhere as cheaply as gas can.

The water flow temperature is lower, so radiators and pipework have to be bigger usually, to get the same amount of heat into the rooms.
Yes immersions are involved to get the water to a higher temperature.

 

[Zerax]

Heat pumps can work very very well... BUT they need to be implemented correctly. I'm led to believe that they are very popular in Scandinavia... where it's a alot colder than it is here !

 

[snowhead]

The reason Heat pumps are grant assisted is the same as Solar panel, wind turbines, biomass boilers etc, none of them are make financial sense without it.

Heat pumps can't heat hot water to tap temperature so can't be instant like Combi hot water, you need to go to a storage cylinder as in the past, or in my case still now, so it can be boosted with immersions.

Correctly designed systems work, but the more a house looses heat through lack of insulation the bigger the heat pump needs to be.
It works in Scandanavia because they've had triple glazing and wads of insulation in their timber buildings for years, but the main reason is they have massive hydro electricity.

 

[plugsandsparks]

Just connected up one of the latest GSHP from Stiebel. Amazing bit of kit.
First thing is that heat pumps can convert 1KW of electrical energy to up to 5KW of heat. Great BUT there is a direct linear relationship between their efficiency and the temperature of the water produced. i.e. to get the maximum efficiency like 5KW of heat from one KW of electrical energy the water is only heated to 35 degrees. The higher the temperature you need the water, the lower its efficiency, i.e at 45 degrees it drops to say 4KW and at 55 degrees it can be below 3KW.

The latest heat pumps can recover the "hot gas" off the compressor getting heat up to 65 degrees, so actually you dont need an immersion heater to get the hot water but its a lot less efficient but still more efficient than an immersion heater.

To get the best out of them, you need UFH as radiators running at 35 degrees would be a lot bigger and quite an ugly solution but to get UFH in a house it is best done at the build stage as your floor needs to be several inches lower to accommodate the pipes and insulation.

The main issue for the older tech heat pumps is that to get the water at 55 degrees the whole heating system had to be run at the same temperature meaning that people never got the real maximum effciency, hence alot of the older ones run at 35 degrees and run immersion for water, with solar panels this can be offset, somewhat

 

[nicebutdim]

Listening to the radio the other day, and UK govt has announce no new gas boilers to be sold by 2035 and everyone should go with ASHP... £5k grant to get one..Let me add... only england and wales. We'll stick with peat up here for now.
The following questions.
Probably easy to answer, but just pretend i'm an idiot for 5 minutes

As an aside; these are devolved matters and, rather than use something similar to the plan worked out for England & Wales, Scotland will almost bankrupt themselves, while NI will devise a plan that's wide open to exploitation and lead to the average homeowner eventually receiving 5% of the expected grant.