Oil boiler sizing - is bigger better?

[Deleted User]

No personal criticism taken.

The issue is that there is not enough info on ASHPs out there and how to best use the heat they produce.

So basically I'm trying to reassure people that they do work in ordinary houses.

The advice from the EST is very general as usual and is a good starting point but believing them as gospel is just plain foolish. Especially since they don't have anyone with the skills to install their monitoring equipment!!!

Makes you wonder if the last trial has indeed any validity whatsoever...

Cheers

PS I do agree that a rad based system will run for longer times but from all my research ASHPs were never indended to be connected to normal rads, even oversized unless perhaps running an HT unit. UFH is different kettle of fish i.e. any boiler will run at lower temps for longer...

Cardew

Jeepjunkie,

I am only interested in presenting what I hope is objective appraisal of heat pumps. Nobody has disputed they can work, but all too often they don't work.

The EST 12 month trial was extended and it is pertinent to note that all of the major manufacturers were involved in the trial, as were acedemic institutions. The level of their involvement is not spelt out, but surely they would have picked up any major error in procedure by EST?

Your contention that ASHPs are not suitable for radiators is not the view of Mitsubishi the manufacturers of your Ecodan system. See:

http://domesticheating.mitsubishielectric.co.uk/

I believe that the claims of all the major manufacturers e.g. 'at least 3kWh output for 1kWh input' should be guaranteed by the manufacturer themselves. As it is they sell their hugely expensive systems to any Tom, !!!!!! or Harry to install.

[Deleted User]

Cardew wrote: »

Jeepjunkie,

I am only interested in presenting what I hope is objective appraisal of heat pumps. Nobody has disputed they can work, but all too often they don't work.

The EST 12 month trial was extended and it is pertinent to note that all of the major manufacturers were involved in the trial, as were acedemic institutions. The level of their involvement is not spelt out, but surely they would have picked up any major error in procedure by EST?

Your contention that ASHPs are not suitable for radiators is not the view of Mitsubishi the manufacturers of your Ecodan system. See:

http://domesticheating.mitsubishielectric.co.uk/

I believe that the claims of all the major manufacturers e.g. 'at least 3kWh output for 1kWh input' should be guaranteed by the manufacturer themselves. As it is they sell their hugely expensive systems to any Tom, !!!!!! or Harry to install.

I have an old EcoDan brochure that shows fancoils/ufh only. I guess rads open up the market by reducing costs at the expense of efficiency?

Rads may suit small well insulated properties where bills will still be reasonable but the target market is surely retrofit for off grid country properties which are typically older/larger and less well insulated where ufh/fancoils are more suitable? All we have insulated is under the floors and CWI which due the age of the house required much investigation beforehand. Windows and doors were already top spec so no drafts.

I say this as villages near us with nice new developments all seem to be supplied by big underground Calor LPG tanks. No ASHP market there.

All the best!

Cardew

Without getting into further dispute, I am not sure I follow your argument.

The Ecodan link I posted gives figures for UFH with water temperature of 35C. I suggest that water at such a low temperature will take a considerable time to get a room up to a reasonable temperature. This is in line with every technical manual I have read - most suggest running heat pumps for very long periods - even 24/7.

It is also pertinent that the outputs of the Ecodan are low in comparison with CH boilers - they are 5kW, 9kW and 14kW against CH boilers that can produce 30kW or more.

TiredGeek

jeepjunkie wrote: »

I have an old EcoDan brochure that shows fancoils/ufh only. I guess rads open up the market by reducing costs at the expense of efficiency?

Interesting. I too have an old brochure, in fact many old brochures (dating back to Feb 2008 when the 14kw model wasn't listed) and mine show normal radiators in the brochures as well as talking about UFH.
They show flow temps of 45'c will give a COP of between 3.1 and 3.7 at 2' and 7' outdoor temps.
We found 45' was ample to warm our place up from ~12' in an hour or so to ~18', which we thought was fine.

While we had our system we played about with it, running it like an an ordinary gas system, running it 24/7, and also tried it with a set back of 4' during the day and overnight.

Now, bearing in mind ours wasn't working right, we found that the 4' setback (20' - 16' - 20' - 16') way of running was the least expensive for us, by about 10%. But that is on costs of £12 / 24hr, so I don't think it means much.
The house felt "right" this way though, not too warm while we were active during the day or sleeping, but nice for waking up to and for sitting watching TV at night.

I am of the opinion that water flow is key with these systems.
For best efficiency, and reliability, the 14kw must have 40 litres / min (or pretty damn close) of water through it. This means 28mm pipe and ideally a low loss header combined with a 15/60 or 25/60 pump.
With this setup normal radiators should do the job if they're oversized.

The major problem I can foresee with retro fitting to a building that has had oil or gas boiler is that the pipework around the building will be run in at best 22mm and most likely 15mm. Fine for "normal" water, but these need antifreeze now and that makes the water more like warm treacle. 15mm + warm treacle and you don't get good flow around the rads.
Go on, ask me how I know
(re-plumb no 1 @ 2009 - remove 15mm pipe wherever it was and fit 22mm, replace 22mm with 28mm)

[Deleted User]

Cardew wrote: »

Without getting into further dispute, I am not sure I follow your argument.

The Ecodan link I posted gives figures for UFH with water temperature of 35C. I suggest that water at such a low temperature will take a considerable time to get a room up to a reasonable temperature. This is in line with every technical manual I have read - most suggest running heat pumps for very long periods - even 24/7.

It is also pertinent that the outputs of the Ecodan are low in comparison with CH boilers - they are 5kW, 9kW and 14kW against CH boilers that can produce 30kW or more.

I think we are dancing round in circles so best just leave it for now...

[Deleted User]

TiredGeek wrote: »

OK, time to clarify
They're out, gone, good riddance
And it wasn't the heatpumps, we think the Mitsi is a good unit which, fitted correctly would work a treat. There were installation and commissioning issues with our system, not the technology.
Hence our mention of not giving up entirely with them, just maybe get a different company to fit new ones better.....

Mixed messages, yep, about right as we are still unsure of the best route to go for the future.

We've been looking at Grant boilers, both indoor and outdoor models. They quote 90+% efficiency (but we'll take that with a bucket of salt) and from what we've seen and heard they're pretty good. They do an outdoor 16/21kw model that should be easy to plumb in as a lot of the pipework is still there from the ASHP

Apparently the new Mitsi controller can manage multiple units and even an oil & ASHP combo, which sounds promising. One 14kw for mild weather use, an oil boiler for frost 'stat and very severe weather.

Hi TiredGeek,

When the two ASHPs were removed... do you know what happened to them? Were they scrapped , used in another installation or back to Mitsi? Just wondered being full of gas and expensive items...

Most appreciated.

Cheers

TiredGeek

Jeepjunkie, see pm

To be honest, if I had some way of getting the thing up to my house then I'd "dispose" of it for you
It would have been useful as a test unit for trying various plumbing configurations before spending mucho money on a final system.... c'est la vie.

Have you considered keeping it for spares for when your's is out of warranty, if you have the space of course.

[Deleted User]

TiredGeek wrote: »

Jeepjunkie, see pm

To be honest, if I had some way of getting the thing up to my house then I'd "dispose" of it for you
It would have been useful as a test unit for trying various plumbing configurations before spending mucho money on a final system.... c'est la vie.

Have you considered keeping it for spares for when your's is out of warranty, if you have the space of course.

Sent PM but yes did consider that but inside the unit other than a spare PCB there is nothing user servicable. Plus with all that gas in inside I guess it should really be used or just scrapped

Seems a shame but as you say if RHI ever happens it won't qualify....

Cheers