Alternative energy / Heating engineers help & advice please

[Smatt]

Hi,
I would like some help with heating system set up please- I am looking into my options....

Current set up:
-Pressurised system run off oil fired boiler running hot water & house heating
-Large house served currently by large capacity old style(but less than 5yrs old) rads in steel with the 'large column cast iron look'
-Rads vary from 5-8kw each (large rooms). Do not have TRVs currently
-Currently 15 rads, but need another 3 at least

I wish to supplement the oil system, ideally with;

-A wood fired stove with integrated back boiler. I like the stovax stoves which have integrated boilers rated upto 8-15kw(in addition to 4-7kw for room heat) depending on model of stove
I realise the house will need much more than just the 15kw max stove boiler output, but would like to use this to supplement/top up the main oil boiler.
This is likely to be in a main family room (fairly close to the boiler/hot water tank) & as such the stove will be used most of the daytime over the winter

AND

-A ground source heat pump

I mainly wish to supplement the house heating as this is the main expense & requires much more energy than the water heating
I know underfloor heating is the ideal for groundsource heat pumps, but this is an old house with many wooden floors so not a feasible option, although I understand large volume rads are next best thing

Questions:
-Is it possible to supplement the energy source whilst retaining the current pressurised sytem? If so how would they interface?
-If not possible, then is the easiest way to separate the heating & hot water systems & change the heating system to a non pressurised, vented system(I understand the stove needs a vented system), whilst retaining the pressurised system for the hot water? What are the problems with this?
-Is it feasible to have 3 heat sources on one system? What are the drawbacks. What kind of controller will be required?
-Would it be better to keep things simple & use just 2 heat sources? If this is the case, then my choice would be the stove/backboiler combined with the oil boiler. -Any problems with this?
-To minimise initial outlay, is it possible to put in the stove/backboiler first, but with the option of adding groundsource heat pump in a couple of years? Will this make it difficult to balance the system later?

What else is there to be aware of?

Alternatively, are there any good forums for this kind of stuff?


I realise this is rather niche/specialist- many thanks for any pointers/help/advice
Matt

 

[Dieselman]

What you really need is better insulation and draught-proofing, then you won't need so much heat.

For the heating why not install underfloor heating under the boards with insulation and spreader plates, then use either a Gnd source heat pump and back-boiler fed via a water cylinder for both DHW and UFH.

You could then retain the oil fired boiler for radiators and DHW back-up as required.

You can run multiple sources of heat into a system but a heat pump isn't going to marry with either solid fuel stove or regular boiler due to the heat differential.
The stove and boiler could work in conjunction on a vented system by using thermostats and zone valves. A couple of friends do exactly that.

I'd go for 3 sources of heat combined with a large water cylinder with solar and backup immersion heater as well. That way you will always have guaranteed hot water and some method of space heating.

 

[Smatt]

Thanks DM
I will obviously maximise what insulation & draughtproofing I can, but it is still a large house with large external surface area, so will always require a fair amount of energy.
It is an old house with solid walls- wall insulation on old houses is not ideal for a number of reasons.

A bit of research has found this, which might be useful.
Also researching wood fired rangecookers with backboilers- Aga don't seem to do wood anymore, so currently Godin seem to stack up as the best for versatility/size/boiler output/looks.

So is the pressurised system incompatible because it is unvented?

 

[Piff]

Talking to a plumber yesterday.
He said air source heat pumps just as good as ground source and you save the cost of digging in all the pipes.

These people Chelmer Heating Services - Underfloor Heating & Renewable Energy - Home may be of interest.

 

[The Hooded Claw]

Ok .........I'm a heating design engineer (Used to be with Brit Gas) now got my own business In answer to the following questions

Questions:
-Is it possible to supplement the energy source whilst retaining the current pressurised sytem? If so how would they interface?
-If not possible, then is the easiest way to separate the heating & hot water systems & change the heating system to a non pressurised, vented system(I understand the stove needs a vented system), whilst retaining the pressurised system for the hot water? What are the problems with this?
-Is it feasible to have 3 heat sources on one system? What are the drawbacks. What kind of controller will be required?
-Would it be better to keep things simple & use just 2 heat sources? If this is the case, then my choice would be the stove/backboiler combined with the oil boiler. -Any problems with this?
-To minimise initial outlay, is it possible to put in the stove/backboiler first, but with the option of adding groundsource heat pump in a couple of years? Will this make it difficult to balance the system later?

What else is there to be aware of?

YES No probs at all

its far too complicated to go into on here I'll PM you with the basic Design instructions

OH BUGGER I aint got enough posts to PM yet !!!! E-Mail me at I'll discuss it that way !!!!!!

Keith

 

[The Hooded Claw]

It EASY to do VERY EASY & It'll cost yer far less than you think

I'll keep checkin my E-Mails until I hear from you

So is the pressurised system incompatible because it is unvented?

WRONG of course its compatable ......Just Mail me I've designed hundreds of Split/Dual/Alt Energy systems

Smatt .....i've "roughed out" a quick design for you just need yer E-Maill addy to send it over I'll send my home phone No as well if you wanna ring to discuss anything your not sure of

 

[Smatt]

Thanks Hoody!
Will send you email.
I would advise editing out your email address now

 

[Smatt]

Talking to a plumber yesterday.
He said air source heat pumps just as good as ground source and you save the cost of digging in all the pipes.

These people Chelmer Heating Services - Underfloor Heating & Renewable Energy - Home may be of interest.

I know airsource heatpumps are cheaper to install. Probably more to the point they are easier, so cynically I might suggest some would be attracted to them as they can still charge loads but with less effort? (No offence intended to any reputable plumbers on here! )

I would plan to do the underground install myself.

However, the energy return/running cost ratio for airsource pumps is less compared to groundsource pumps. ie there is less net energy gain with an airsource pump- I beleive it is 2-3:1 energy gain for airsource & approx 4:1 gain for groundsource.
Plus I understand they are not so useful over the winter when it is particularly cold(when it is most needed?). In comparison, a groundsource pump is a more constant provider of energy (obviously air temp fluctuates more than underground temp).
Airsource pumps are probably better in slightly warmer climates & also in urban areas where there are less extremes. Ours is a very rural location.

However, I am no expert, so await correction....

 

[The Hooded Claw]

Hi Matt just sent that e-mail over to you ......Airsource heat pumps only "Recirc" warm air from other areas of the house

i.e. if the missus is having a shower the heat generated in the bathroom is collected & recirced to other rooms using up the useful heat

Airsource heat pumps are good for houses that suffer from condensation as they "Move air around the home" & do not let it "Settle" on "Cold spots" & cause mould & other nasties to grow

 

[Smatt]

Got it thankyou.

I think that is a 'heat recovery system' you are referring to, which expels internal damp air, but extracts the heat from it to warm incoming air.
Airsource heat pumps are external & gain energy from the outside ambient air & then use a heat exchanger to convert this to heat water for hotwater/heating

 

[Baron_Samedi]

Have a look on wikipedia for info on ground sourced heat...

It isn't as easy as it seems...

 

[Dieselman]

My understanding is that smatt is correct with his efficiency calcs, so a Gnd source pump costs more to install due to boring/digging, but is considerably more efficient on operation due to recovering heat from a more constant and warmer source.
In addition they are quieter as there are no external fans.

As far as a solid fuel stove being run as part of a pressurised system I'm still not sure about hat as it would then fall under the requirement of steam boilers and require regular testing and certification.
Maybe that's not the case though I can't see rules being relaxed.

 

[Smatt]

Yes, I forgot about the noise- the airsource pumps are a fair volume & of course have to have a good airflow. So they can not be screened off particularly, meaning the noise can radiate more.

 

[w124coupe]

My understanding is that smatt is correct with his efficiency calcs, so a Gnd source pump costs more to install due to boring/digging, but is considerably more efficient on operation due to recovering heat from a more constant and warmer source.
In addition they are quieter as there are no external fans.

As far as a solid fuel stove being run as part of a pressurised system I'm still not sure about hat as it would then fall under the requirement of steam boilers and require regular testing and certification.
Maybe that's not the case though I can't see rules being relaxed.

We have a ground source pump - a few years old now - which achieves about 3:1 (still a LONG payback versus gas if you can access it).

The air source pumps are just too dependent on the weather - dip below zero and they fail to be efficient enough JUST when you need the most heat.....(for most of our relatively poorly insultaed/hard to upgrade UK housing stock anyway - different if you have a pupose-designed super-insulated home).

We have a probe in the trench with the pipes - the temp stays about 12C all year round - heated by the earth's core(!) - too deep for UK weather to affect it much.

 

[Rory]

Got it thankyou.

I think that is a 'heat recovery system' you are referring to, which expels internal damp air, but extracts the heat from it to warm incoming air.
Airsource heat pumps are external & gain energy from the outside ambient air & then use a heat exchanger to convert this to heat water for hotwater/heating

I'm sure I've seen heatpumps used in heat recovery systems to multiply the effect of the recovered heat.

On the face of it, it makes perfect sense as the extracted air would be pretty warm to start with - unless there's simply not enough volume of air?

 

[Dieselman]

I'm sure I've seen heatpumps used in heat recovery systems to multiply the effect of the recovered heat.

On the face of it, it makes perfect sense as the extracted air would be pretty warm to start with - unless there's simply not enough volume of air?

Heating the air being blown into or wafted round a building is inefficient anyway, heating the building substrate is much more efficient.

 

[The Hooded Claw]

I'm sure I've seen heatpumps used in heat recovery systems to multiply the effect of the recovered heat.

On the face of it, it makes perfect sense as the extracted air would be pretty warm to start with - unless there's simply not enough volume of air?

Airsource heat pumps DO INDEED have "Heat Recovery vains" fitted within each unit thats what I was refering to in my earlier post, there is insufficient warmth in "average" ambeiant air to make them a viable proposition UNLESS a internal recovery unit is installed in "Series" with the unit.

ALL heating systems are designed on a "degree Day" basis i.e, the calc assumes it is -1 outside & you require say 21 in your home A stand alone Airsource heat pump will give NO MORE than 500Btu's (based on the same calc) where-as when the Heat Recovery is introduced that figure increases 10 fold or 5000Btu's (enough to heat a cube approx 10 feet X 10 Feet X 8 feet to an average temp of 20 degrees C)

 

[Smatt]

The terms 'Heat recovery (ventilation) systems' and 'airsource heat pumps' , as per general useage today are completely different systems & should not be confused. They can obviously be combined in the same house.
A commercially sourced airsource heat pump for the domestic market may give enough energy to heat an average home & its water, hence can give much more than 500BTUs energy

 

[The Hooded Claw]

The terms 'Heat recovery (ventilation) systems' and 'airsource heat pumps' , as per general useage today are completely different systems & should not be confused. They can obviously be combined in the same house.
A commercially sourced airsource heat pump for the domestic market may give enough energy to heat an average home & its water, hence can give much more than 500BTUs energy

Not without a buffer vessel it won't, the 500BTU's i refer to is the AVERAGE output from an Airsource on a Degree day ( As previously mentioned -1 degree outside) Buffer vessels (such as Gledhill's Thermal Store) take the heat generated from the airsource & heat the stored water, it is THIS water that is then pumped around the radiators it may take "Some Time" to bring the thermal store up to a "Usable" temperature the domestic Hot Water is provided via a finned Coil inside the thermal store, the mains cold water passes thru this coil & heat is transfered to it( giving hot water for showers/baths ect)

An Airsource heat pump installed without a Thermal Store will provide little (if any) useable heat Every Airsource manufacturer design I have ever seen has a "Small Immersion Htr" installed to "Boost" the output.

As a side issue Building regs Part L (Domestic) state "a High efficiency / Condensing boiler MUST be installed, where-as Building reg L part 2 (Commercial) states "A high efficiency / condensing boiler SHOULD be used "where appropriate"

In "Laymans" terms Commercial properties DO NOT HAVE to have a Condensing boiler installed to comply with the regulations, merely it is "advisable to do so"

& then we come on to the Legionella problem, Most new boilers have a "sanitation" programme built into the control packages If water is stored at (or around) 40 to 45 degrees there is a possibility of Legionella growth the "sanitation" programme boosts the hot water to 90 degrees once every 24 hours (Usually at around 2AM) killing any Legionella bugs present within the hot water system.

Therefore a "Stand Alone" Airsource heat pump would be next to useless in complying with the current Legionella regulations.

 

[Smatt]

I am not interested in airsource pumps myself, I was pointing out that they are quite different to heat recovery systems which you were referring to.

It is recommended that DHW is kept at 55deg plus to avoid legionella.

Regarding airsource pumps:
In a traditional boiler system with rads(which ours is), an 'air to water' system will be needed, there is no significant risk of Legionalla with this; this is a problem with the 'air to air' pumps, airconditioning systems or open water systems such as spa baths. An airsource pumps' energy 'collector' is outside. Fluid coming from the collector is in a closed loop; there is no direct mixing with water in the heating system.

A typical average sized radiator in a house might be 1-3 kw, depending on size of rad. A typical airsource heatpump can provide upto 10-20kw depending on the size/cost of pump. Obviously they will not work as well the lower the ambient ext temp & may require top up from other sources.

The ideal situation for ground or air source pump is to have a constant circulation via underfloor heating