oil to air source heat pump

Reed_Richards

orbit500 said:

I figured on best of both by using a 4 port 300l direct buffer and all smart TRVs with a 42kW boiler.
Heats up astonishingly quickly but equally can run a single towel rail with boiler firing only when buffer cycles its 20c hysteresis stats.
Although on oil, when I refurbished I doubled all rad sizes for 40c flow so putting 60c water through them heats up in a blink of an eye. Nice when you come back from a winter holiday

This seems very well thought-out.  You have greatly over-sized the radiators, which I'm sure is the most effective way of ensuring that a house heats up quickly from cold (assuming your heat source can meet the required output).  But you have a buffer system to mitigate against short cycling, which would tend to occur as a consequence of the oversized radiators.

orbit500

The biggest issue I faced was complete disinterest from ‘heating engineers’, aka Dave the plumber, in engineering solutions to long standing issues. I designed it from mainly German sources and my own physics background.

QrizB

Cardew said:

Also a gas boiler will heat water to 80C+ not 65C

It might be capable of heating to 80C, but that doesn't mean you should do it (and this would make the ASHP faster than the gas boiler).

Similarly the ASHP might be capable of heating to 65C, but practically no-one would recommend doing so.

The output of a nominal 10kW ASHP falls with lower ambient temperature.

I'm not clear how this is relevant?

toadhall

Thank you to everyone for your comments.
I am mainly looking to  have ASHP because there appears very little choice for anything else.
I have no mains gas supply.
My oil boiler has been condemned. Yes I could replace it but the tank is also close to the end of its life and would have to be repositioned due to new regulations and there is nowhere else to put it.
I could have a gas tank installed, but again there is nowhere to put it.
Electric boilers are far too much to run.

I am having surveys and quotes at the moment and looking hopeful for the ASHP option, I have read all the comments and while I do not profess to understand everything and all the figures, I think it may be the best option for us.

Cardew

QrizB said:

Cardew said:

Also a gas boiler will heat water to 80C+ not 65C

It might be capable of heating to 80C, but that doesn't mean you should do it (and this would make the ASHP faster than the gas boiler).

Similarly the ASHP might be capable of heating to 65C, but practically no-one would recommend doing so.

The output of a nominal 10kW ASHP falls with lower ambient temperature.

I'm not clear how this is relevant?

I think we must be at cross purposes.

The aspect I raised was the inability of an ASHP to heat a house quickly from cold e.g. after heating being off all day or at night.

A gas/oil boiler can blast out maximum output regardless of outside ambient temperature. An ASHP has a much lower maximum output and this reduces as the ambient temperature falls.

I really cannot see how you deduce an ASHP would be faster than the gas boiler.

lohr500

toadhall said:

Thank you to everyone for your comments.
I am mainly looking to  have ASHP because there appears very little choice for anything else.
I have no mains gas supply.
My oil boiler has been condemned. Yes I could replace it but the tank is also close to the end of its life and would have to be repositioned due to new regulations and there is nowhere else to put it.
I could have a gas tank installed, but again there is nowhere to put it.
Electric boilers are far too much to run.

I am having surveys and quotes at the moment and looking hopeful for the ASHP option, I have read all the comments and while I do not profess to understand everything and all the figures, I think it may be the best option for us.

Thanks for the feedback.

If there is absolutely no way to install a new tank (oil or LPG) then it would appear as though ASHP is your best alternative.

If you haven't done so already, I would seek advice on a replacement tank from a number of sources, so you can be 100% sure that replacing the old one in the same location is a no/no (Even if you had to install some extra fireproofing). If it was me, I would be exploring this option to death before pressing the button on an ASHP system.

Patrol

orbit500 said:

The biggest issue I faced was complete disinterest from ‘heating engineers’, aka Dave the plumber, in engineering solutions to long standing issues. I designed it from mainly German sources and my own physics background.

There's probably good reasons for this. Presumably a heating engineer goes on what they have been taught plus what they learn hands-on. Unless they like taking risks why try something new, or more complicated due to extra components or untried theories. If it goes wrong they are on the hook and their reputation or livelihood suffers.

Traditional gas and oil heating may well have been "good enough" for many years when fuel was cheaper. I do wonder how much more efficient they could be but doubt the average one man band or small company would want to invest time and money in trials. My GSHP was installed with no mention of options that I later learnt of  (do I want a buffer tank, should I have a shunt/pig valve for my upstairs radiators) and I suspect the same is true for many ASHP installations.

I could be wrong, there may be ongoing research about best practice for heating systems which in light of increasing fuel costs and environmental concerns would be nice to hear more about. It is interesting to read posts such as yours which describe a different way of thinking (oil plus buffer which may not be revolutionary but is to my simple mind almost the reverse direction to a combi boiler?)

Reed_Richards

When you first encounter heat pumps they seem almost magical with their ability to convert electricity to heat with an efficiency of over one hundred percent, maybe typically about three hundred percent in fact.  Perhaps as a result of this, they often seem to be surrounded by an air of mystique and mysticism which causes some people to believe unlikely things about them without question.  The way their efficiency varies with operating conditions takes a bit of getting your head around but fundamentally they are just another heat source like a gas or oil boiler.

My heat pump can achieve its full rated output down to an outside temperature of -7 C and 80% of its rated output at -20 C.  So if I want it to blast out its maximum output in order to heat the house quickly it's very unlikely that it would be so cold outside that I could not do that.  Whether letting the house get cold then rapidly bringing it back to temperature would be the most economical way to ensure my house is warm enough when I want it to be is another matter.  That's usually the most economical way to use a gas or oil boiler but not necessarily a heat pump.  

QrizB

Cardew said:

I think we must be at cross purposes.

That's definitely possible.

A gas/oil boiler can blast out maximum output regardless of outside ambient temperature. An ASHP has a much lower maximum output ...

A gas boiler (or any heat source) can only blast out heat at the maimum capacity of the emitters (radiators etc.). If I had a monster 36kW boiler connected to a single 1865W radiator (example) it wouldn't be able to blast out any more heat than a little 9kW boiler could.

... and this reduces as the ambient temperature falls.

Nevertheless, so long as the remaining output equals or exceeds the capacity of the emitters, the loss of output will have no significant effect.

I really cannot see how you deduce an ASHP would be faster than the gas boiler.

I don't believe I've claimed that at any point in this thread.

Meanwhile, I don't see how you can claim that a system using an ASHP will necessarily be slower than one using a gas boiler.

born_again

Interesting thread.
One thing is ASHP require larger radiators in many cases. So how does that work when your radiators are already to the point of covering all the under windows & available space in hallways. Do they have to go higher. Making them triple rads is not going to happen in hallways due to width. In most of our rooms there is no spare wall space that is not blocked by a piece of furniture. 

Would you end up having to go for say blown air heating?

Interesting times....