Green Building Forum - Heating and cooling

Ducted air to air heat pumps

owlman — Mon, 09 Nov 2015 19:25:34 +0000

Does anybody have any experience with these units in a domestic interior?

'Best' smart heating control system to retro fit to combi gas CH

wellburn — Sun, 18 Aug 2019 18:04:00 +0100

I have a well insulated mid terrace 3 story home, with irregular occupancy.
Single zone heating system, currently just on manual timer, but wanting to install some kind of 'cleaver' system pre winter.
New Baxo duotec 33es - not 'OpenTherm'

About 10 rads, - all with compatable TRV controllers and I budgeted for smart rad valves.
Many options, Honeywell, Drayton, Tado etc

Really like the idea of control via App, so can tweak heating when in or out for comfort & savings.

Any experience with any systems or advice.

:confused:

Many thanks

retrofit 'opentherm'

wellburn — Sun, 18 Aug 2019 17:57:57 +0100

just wondering if it is possible to retrofit an opentherm module to a new(ish) baxi duotec condensing boiler?

Without Opentherm, - can only switch on / off full blast, so frequent overshoot

Still a current model, so cannot justify upgrade.

any thoughts?:confused:

Woodburner above thermal store

Penkestle — Fri, 09 Aug 2019 15:18:56 +0100

I need to call on the experience of you guys
Our main heating/hot water source we are undecided on. I would prefer a wood burner with back boiler but the barn conversion being an upside down arrangement with vaulted ceilings would mean that the woodburner would be above the thermal store. My research to date suggests that this is very difficult to implement. There is a small attic area that would hold a header tank and a heat sink rad which is approximately 2m above the woodburners position. Space in this attic would be limited so it would be likely that the space wouldn't be sufficient for the size of rad required. Utilising the Towel rads as a heat sink would be the ideal but again with the upside down arrangement gravity feeds can't be implemented. A woodburner would be installed regardless so having that facility to heat water from it would make good sense that and the fact we have access to a plentiful wood supply. My wife prefers the option of an air source heat pump which regardless of which way we decide to go I have already run in pipework and electricity supplies to accommodate. I guess my reluctance to go down the air source route is having a gun held to my head by the electricity companies and the ridiculous price that they are. I would really like to hear your thoughts on this and any info you might be able to provide regarding the woodbuner back boiler situation and the air source arrangement. Thanks In Advance

Super insulated dwellings

owlman — Thu, 25 Jul 2019 16:25:50 +0100

Heat waves are supposed to become more intense and more frequent as GW bites.
Super insulation obviously works fine in the winter, but is it in danger of turning our dwellings into hotboxes in Summer?
I arrived home late last night and the outside temperature was 16.5C In spite of windows and roof-lights being open and a oscillating fan on, and a relatively open plan interior, the living room was at 26C.
When I finalise the duct-work to my A2A system, hopefully it'll be a thing of the past.

'Remote' Control of electric heating

Nick Parsons — Sun, 12 May 2019 14:07:53 +0100

I am looking at a village hall with heating via fixed elec panel heaters, 2 stand-alone elec heaters and an apparently very disappointing ASHP with claimed output of approx. 3kW.

The hall was built in 1998/99, should have U values of 0.45 (walls), 0.25 (roof) and 0.45 (floors). How 'tightly' it was built is not known, although there is generally 200 - 300mmm in the roof. User experience suggests that, particularly for activities involving being on the floor, it is not perceived as warm.

Use of the hall is regular, but quite low, suggesting that the best short-term 'fix' might be remote control of the existing heaters rather than any replacement of heaters at this stage.

There is no mains gas in the village.

I am not an electrician, and do not often deal with electric heating.

Has anyone used 'remote' control of electric heating, either via an on-site multi-option controller or something accessible by mobile phone?

Thanks,

Nick

Gothenburg, Sweden

minisaurus — Sat, 13 Apr 2019 15:01:47 +0100

Hi,

I thought some of you might be interested in the work of my council's energy company - GÃ¶teborg Energi. A limited company owned by me and the rest of us taxpayers here, GÃ¶teborg Energi manage, amongst other things, both the local electricity network, and the local "fjÃ¤rrvÃ¤rme" network - "remote heating" network. They are now nearly completely fossil fuel free - it's only in harsh winters like last march (2018) that they had to fire up a couple of their older oil boilers.

Most of the city's central heating comes from heat recovered from two giant waste incinerators in Utby, east gothenburg (this process has however resulted in particles falling into the nearby sea). The other main sources of heat are via heat pumps installed in the city's sewage processing plant, heat pumps installed in the port's oil refineries, and heat pumps in the river. Scaninavia's biggest solarcell park has just gone online in SÃ¤ve north west of the city centre.

Almost all the flats, offices and industrial parks in gothenburg are connected to this heat network, and a large portion of the houses. The model is repeated in almost all Swedish municipal areas.

GÃ¶teborg Energi have even recently built and installed China's first "remote" heating plant, which also uses Swedish automation.

Their success is due to many things - the relationship with Chalmers University, the freedom to experiment, and I'm sure the stability afforded by their owners - Gothenburg Council - who's revenue stream is local people's income tax. This means the council has no dependency on central government for finance, so are free to make their own plans.

You can read more about GÃ¶teborg Energi here: https://www.goteborgenergi.se/english/about-us

Overheating

Cerisy — Sat, 09 Feb 2019 11:12:06 +0000

I've posted before regarding our issues with overheating last summer for the hot weeks we experienced here in Normandy. Our new house is insulated to PH standards and we struggled to lose heat. This is forecast to be an increasing issue and as we are not "spring-chickens" we need to address the problem.

Our MVHR unit is a Titon with summer bypass. Unfortunately the Titon summer bypass is automatic and cuts in when the air coming into the unit is hotter than the air being expelled. As the supply pipe comes through the loft, which of course gets very hot during the day, it kicked in during the afternoon. I quickly disabled the summer bypass so it didn't pull in hotter air and as it sounded like we were living next to Heathrow! So what to do for this year ...

Firstly we can simply switch off the MVHR when it gets silly hot and use our tilt turn windows at night to reduce the temp in the house and freshen the air (why didn't I think of that last year? Probably as I fitted the system and it seemed counter intuitive to switch it off!). Secondly we could replace the Titon with a alternative model that has manual summer bypass that we could use at night - still switching off the unit during the day.

The end game I guess is to install air-conditioning - one downstairs and one in our bedroom. They would need to be linked to installing PV to cover the electricity usage of course, but as the cost of that drops maybe not too expensive, even in France!

Any thoughts guy? Regards, Jonathan

Straw Bale House heating needed?

Nedington — Tue, 05 Mar 2019 23:00:37 +0000

My partner and I are planning to build a 2/3 bedroom straw bale house. 1 of the challenges is trying to figure out the right heating systems. We have been told by straw bale experts that underfloor heating and/or a wood burning stove would make the house too hot. We plan to have quite a few windows south facing, but as this is the UK, we find it hard to believe no heating is needed. thoughts?

UFH between timber joists - spacing?

Sprocket — Tue, 26 Feb 2019 16:02:51 +0000

Refurb of an upside down house (ie. Upstairs is main living space).
Floor upstairs will be 20mm engineered oak boards directly on top of timber joists

UFH pipes that are all to be replaced are supported in trays between the joists. How important (or not) is UFH pipe spacing?
I can see it being tricky to get 100mm spacing here, and even if we can, surely the heat delivery is limited by all the air around the pipe?

Might there be some interesting but practical solutions to this that I am missing?

CH/DHW system w. boiler-stove, solar and heat store - needs improving

IanCD — Thu, 01 Feb 2018 11:56:25 +0000

Currently renovating old stone-built detached house, insulating walls internally with 100mm multipor.
We have 2 solar thermal panels fitted (Viessman 200), and a Morso DB15 boiler-stove heating a 300l heat store. Heat store also has 3kW immersion heater.

It's our first full winter in the house after living in a caravan-in-a cabin for most of the previous four and a half years... so even with problems this is luxury..!

We're using half the house at the moment:
- the kitchen where the boiler-stove is fitted (5.2m x 4.3m x 4.5m to the apex ceiling); this room also has a 2.6kW radiator
- the bathroom, which has a 1.1kW radiator, also the heat leak radiator for the stove and low power (290w) electric UFH
- bedroom, which has piped UFH at 150mm spacing, and is 12m2

We find that the stored heat from running the stove the previous day (and topping up with the immersion heater for a couple of hours if necessary from 5am to 7am) brings the heat store temp up to about 60c middle to top. The temp in the bottom depends on how hot it is fromn the previous evening.

This gives us enough HW for 2 good showers and some left, but is insufficient to run the CH.
We find the temp in the lower half of the heat store - where the CH water is drawn from - drops quickly as soon as we run the CH.
We can get the whole store up to 60c+ after running during the day, so that we can run the CH for an hour or so in the evening. The bathroom usually stays very warm without the radiator drawing any heat from CH and the kitchen radiator thermostat is turned right down to conserve CH supply heat, so we're only using the CH to warm the bedroom via the UFH. We find we can run the CH for an hour or so and that will bring the temp up about 1degree - usually sufficient to warm the (bare concrete!) floor - but that will drop the temp in the heat store, maybe unless we have the Morso running flat out... It's the Pure Wood model and we're still experimenting with wood supplies and getting to the point where we have sufficint well-seasoned wood stored for a whole winter.

There is never enough heat stored in the morning to be able to run the heating.
Part of the issue is that even if we get the thermal store really hot by the evening - and we have had it up to 80c a few times - it will lose that heat by the morning. Some along the copper pipe runs, some from brass fittings around the heat store.

We are meeting with the heating engineer soon to look at options. One possibility may be retro-fitting a backup LPG boiler and somehow linking it to the system: there are spare tappings in the heat store toward the top and at the bottom, although it would involve dismantling some of the finished work on the house.
Another option I'm wondering about is somehow installing an additional heat store and linking this in to the existing one, using those same tappings, to give a much larger overall volume of water, and of potential stored heat. This would have to be located in the utility room, which is on the ground floor, so below the existing heat store.

We will have to look at the feasibility of the LPG boiler with the heating engineer, but I thought I would ask here about the idea of a linked second heat store. Does anyone here know if that's feasible, and how we might control temperature and flow of water between the two?

A couple more questions related to this situation:
1. Following guidance (mistakenly) that came with the stove, we fitted a pipe thermostat to the boiler-to-heat-store output pipe rather than a flue thermostat. This is set at about 65c but it means that, if the water at the bottom of the heat store is over 60c, water continues to circulate through the stove for some time after the fire has died down, which can deplete stored heat.
A flue thermostat would be better but the heat store is on the other side of a 700mm thick wall, a metre or so (with a floor/ceiling between) above the boiler-stove. All the walls are finished (lime plastered) and all the pipe work connected so we can't run a cable from a flue thermostat to the heat store.

Does anyone know of a wireless solution, by which we could connect a flue thermostat to a wireless transmitter in the fireplace and the signal be received on the other side of the wall where the heat store is located?

Lastly, any suggestions for the best way to insulate all those brass components on the heat store and pipework?

Ian

Heat output kWh per kg from small pellet boiler-stove?

IanCD — Fri, 08 Feb 2019 15:03:15 +0000

This is something of an update to a previous discussion here: http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15542&page=1#Comment_265315

I wrote to the suppliers of the Morso DB15 and heat store in June last year, the outcome f which is that we've just had an MCZ Gardenia Hydro pellet boiler stove fitted - I think pretty much at cost price, with the company paying for the installation at no cost to ourselves. So, a pretty good outcome and it means we're still getting all our heating and hot water from renewables.

It's early days, so there's probably still some tweaking to be done on settings but we're not getting the output per kg that was predicted. The output is metered and it's a small hopper feed with bagged pellets so I know how much we're getting per kg. The performance estimate was just under 4kWh per kg (3.96) but we're actually only getting just over 3kWh/kg, which obviously makes running costs considerably higher.

Do any of you know why this might be? We've reduced the pellet dosing as far as possible (-30% from default) but it doesn't seem to have made much difference to the output, though the brazier and glass are staying cleaner. I think the company are going to check the flue draft as well - if they haven't already - as I understand that can make a difference.

Do the pellets (all EN plus A1 and BSL certified) vary much in heat output from one manufacturer to another?

Regards,
Ian

Heating Controls - large family home

Modelmechanix — Wed, 06 Feb 2019 13:23:27 +0000

Hi all,

Iâ€™m looking for heating control options to put my UFH and Rads on the same central control system.
I have 8 UFH zones (ground floor) with 12 actuators plus 5 Rad zones with 7 rads (first floor).
Shortly be adding heating to the basement, probably rads but UFH not ruled out yet.

Iâ€™ve seen Evohome and Max! and a few others but prices vary wildly, as do user experiences.
What are people here using?
Any real world experience (good or bad) to share?

N.B. Have seen the recent discussion on heating controls by Lineweight but as my project is unite different, I thought Iâ€™d start a fresh thread.

Thanks, Karl

Zoned heating controls - retrofit-friendly

lineweight — Sun, 22 Nov 2015 13:49:43 +0000

2-bed flat, recently refurbed to be well insulated. Occupancy patterns are a bit irregular because some days I work from home, and I also have a guest room which is occupied some nights and not others.

At the moment I have combi boiler on programmable timer, and TRVs in each room but I want something more flexible and which is easier to control on a day-to-day basis. Also ideally I'd like it to be possible to control the temperature in the guest room from within the room without affecting the rest of the flat.

I only need 3 or 4 zones.

Options I've investigated so far -

Honeywell Evohome
Looks like nice UI and good level of control and can do what I want. Expensive though. Prob around Â£400 for my needs.

Heat Genius
Looks like it can do what the Evohome does, but with some additional options like PIR sensors for automatic control based on occupancy, and the ability to record data over time. Seems to be even more expensive than the Evohom though, Â£400+

Homematic
This looks like it could probably do what I want (plus quite a lot more as optional add ons in the future) but is a German system without much info in English and looks like it could be a bit involved to do the setup. UI doesn't look terribly user-friendly. A bit cheaper than Evohome or Heat Genius but not much. Maybe Â£370.

eQ-3 MAX
This is much cheaper than the others (Â£150ish) and looks like it can do what I want but it doesn't seem to have any control over the boiler itself - basically just assumes that the boiler is already on. This seems a major drawback to me. There are some diagrams here:

http://ecohousecomfort.com/termic-zone/max-range.html

which suggest how to deal with this but neither seems satisfactory. Either you have the boiler on a wall switch which is turned on/off by a centrally located stat. But this stat doesn't seem to communicate with the others so as far as I can see you will end up either with the room stats calling for heat and not getting it because central stat has shut boiler down, or central stat has switched boiler on but none of the room stats want any heat.

The other option seems to rely on the boiler's own protection circuit switching it off if all the room valves are closed and the return flow is coming back hot. But won't this just leave the boiler endlessly switching on and off, when there's no demand form the room stats? That doesn't sound like it would be very good for the boiler.

Does anyone have any experience of any of these systems, or suggestions for others to look at?

And is my concern about the endlessly cycling boiler with the MAX system a reasonable one, or isn't it really an issue?

'Best' regular gas boiler

jms452 — Sun, 03 Feb 2019 16:34:25 +0000

Hi all,

What is the current consensus on high efficient high reliability regular gas boiler?

Heat demand is lower following renovation so the 15kW boiler we've got could possibly dropped to 12kW.
Considered:

Valliant - ecoTEC plus 412 (4.7 - 12.8kW)
Atag - i15S (14.7kw)

The lower & variable heat output and wider range of repair expertise is probably pushing me towards the Valiant - but interested in opinions here. Also is there anything I should be looking for or requesting to make the system work better while I'm at it?

Currently:
Old system boiler - embarrassing efficiency about 75% for heating
9 largish mostly double radiators on 15mm pipes
well insulated hot water tank and two cold tanks in loft.
basic controls.

Considered the FGHR combi option but decided against this as:
We may add solar hot water so want to keep the hot water tank
We live in a supper hard water area and I'd rather have scale in the hot water tank than in the boiler (and don't want to add a water softener).

System Boiler to Combi?

Victorianeco — Wed, 23 Jan 2019 10:32:01 +0000

Looking at property refurb project, currently has a 10yr old system boiler and cylinder. Looking to put in a new boiler not necessarily because it needs one but for increased saleability...

New system boiler - easy plumbing, swapping like for like

or

Combi - A lot more plumbing, no standing heat losses, greater appeal to buyer perhaps?

I have come across the Intergas Rapid model which can actually be used as both mind...

Thoughts?

How to improve on a gas boiler for hot water economically

GarethC — Thu, 03 Sep 2015 09:54:28 +0100

You've all heard my grand (ok, not really) plans to use A2A heat pumps to reduce, hopefully, the carbon (by 40%) and cost (by 25%) of my space heating compared to my current, high efficiency combi gas boiler at reasonable installation cost (circa Â£2k).

I can't for the life of me decide what I, or someone in my position, would do about DHW, though. The economist in me says that, given the current cost of my hot water, any solution would have to cost about Â£1k installed maximum, and preferably Â£750. Can anyone think of a system that provides hot water at significantly lower cost and carbon than a natural gas boiler for this amount? Or are usage reduction measures the only sensible way to go?

Just let me know if I've missed any recent threads on this question.

thermostats

Boreas — Mon, 03 Dec 2018 10:44:48 +0000

Hi Guys,
I have two simple heating circuits running off a thermal store; one is the UFH and the other a towel rail then radiator (in series). At present, the control for the pumps running is locally on the store and they are bimetallic thermostats (the old kind) which make the pumps run too long which is a waste of power and hot water (and cash).
I don't mind the set up as is as it's simple but need a much more accurate switch on/off stat. For example, let's say the rads are set to come on when the store temp reaches 40 degrees. I need a thermostat which measures when the water is drops below this temp (or whatever is set) that makes the pump stop running and not at say 30 degrees. The units must have probes which slot into tubes in the store. There is no control in any rooms, like I said before only local on the store.
Looking forward to your comments.

Thank you , Nick.:surprised:

Thoughts on floor coverings for upstairs UFH?

Sprocket — Sun, 11 Nov 2018 11:39:02 +0000

Our next house is about to get a major make-over before we move in. Old heating system is 22 yr old polybutylene pipe throughout so it ALL needs to go. Downstairs is in thin screed so we just dig it up and replace (in Pex-A).

The upstairs UFH has more to think about. Living space is upstairs, beds downstairs and whilst it will be fairly draught-free and well glazed it is by no means an modern eco-build. There are a few gas fires but I would like to spec to get all the heat from UFH if we can.

Considering using some sort of UFH pipe-guide system with 100 or 150mm pipe spacing incorporating insulation and reflective surface although of course this would sit on top of joists so will raise all the floor levels a little. But what to put over the top?

The numbers make we want to put ceramic tiles everywhere but I'm also concerned about rigidity of the floor and possibility of losing all the grout to cracks with movement which makes me want to put thicker backing board over the UFH... which of course stuffs up the heating. My wife is wondering about timber floors, maybe a bit of parquet; oh and carpet in the upstairs master bedroom (and boy does carpet+underlay stuff up the numbers). Anything with glue also limits my below-floor temp to 27 degrees so I can't just raise UFH temp to get more heat out.

Is there a major solution to some of these problems (from flooring over UFH on floor joists) that I might be overlooking? Particular UFH systems I should look at? How much decent support for my flooring can I get from the UFH and how much (and what) do I need to consider putting over the top eg. for tiles?

Any thoughts/ideas appreciated.

Looking for an electrician experienced with an MVHR duct heater in SE London

richardelliot — Sun, 11 Nov 2018 20:06:43 +0000

We have a VEAB duct heater on the intake to our MVHR unit. Last winter during 'the beast from the east' I noticed that it never turned on. It wasn't something I tested when we did the handover of the house with our builder so I'm not sure if it is ever worked (so it could be faulty or not installed correct).

I'm keen to get it fixed before this winter but struggling to find an electrician who is experienced with the units and will come and take a look. Has anyone on the forum had one installed and could put me in touch with an electrician who knows how they work? I'm based in South East London.

Link to the heater:
https://www.veab.com/en/veab-produkter/kanalvarmare-elektriska/cv.html

I've tried some basic trouble shooting myself, but really don't know what I'm doing with electrics. The builder who built our house sadly had some ill health so decided to retire and close down his firm so I cannot get them back unfortunately.

Is it OK to connect PEX directly to HW Cylinder?

andyman99 — Mon, 12 Nov 2018 21:00:03 +0000

Can PEX plastic pipe be directly connected to a vented hot water cylinder? I'm using it in most places with the exception of the first metre or so to the boiler, but wondered if there are any other restrictions. I can't seem to find any in the Speedfit literature, but just wanted to double check. Thanks

Sharing coil in thermal store

Modelmechanix — Sun, 09 Sep 2018 16:11:10 +0100

Hi all,

My name is Karl, this is my first post but Iâ€™ve been reading and researching using this superb forum for quite a while now.
Thank you all for sharing your obviously hard earned knowledge, it really is appreciated and has help develop my knowledge and interst in renewables and heat engineering.

I have a question which I canâ€™t quite find a definitive answer to, having searched for a while.

Is it ok to you use one coil for multiple solar thermal inputs?

Some background and sorry if this is too much info but I have seen from general responses here that the more detail, the better able people are to provide input.
I have an existing 3 coil 1000ltr thermal store supplying my DHW via a full height stainless steel 7.5m2 coil, works brilliantly.
Direct connection (store is open vented) of a 24kw wood burner via laddomatt and digital stove control. Rarely used except for depths of winter when the family really enjoy the live flame experience and I get that smug satisfaction knowing that we are loading the thermal store with heat too.
Upper coil, 2m2 supplied by 15kw pellet boiler, tops up my DHW on less dull days and via 2 port valve inputs heat to the UFH when needed (mainly early hours of morning (2-6 am) all very efficient.
Lower coil 3m2 supplied by 6.6m2 flat plate solar thermal, provides 100% DHW production for c.8 months of the year. Remaining 4 months it contributes c.50% DHW and some (c.40%) space heating as UFH take off is 60% up the store so once the temp sensor at 60% hits 40c the heat is pumped to the UFH until the temp at 60% drops to 35c. So the UFH gets 40c input from solar most days during heating season, average is about 1 hour recovery from 35c to 40c for the store for 15 mins supply to the UFH all whilst keeping the upper 40% at DHW temp, very happy with the stratification.
I now have an additional 50 EV tubes to add to the system but no more coils available. Iâ€™d like to T into the lower solar coil and use it for both solar arrays, (existing flat plate and new EV tubes) obviously running through separate pump stations with non return valves and separate controllers. I have some direct connection ports left so running through a PHE could be another option but would involve more pumps and more plumbing. Not my preferred option.

Could I ask what people think about sharing a coil for two heat inputs?
I have seen it done before for oil CH when a boiler stove has been added so I know itâ€™s technically possible and accepted practice in some places. I have never seen or heard of it done with solar though.

Many thanks in advance for all replies,
Karl

CH & DHW oil boiler - Heat Loss and DHW demand

LAS1404 — Wed, 31 Oct 2018 15:06:52 +0000

Hello all - we are half-way through a low energy build. We are not on mains gas - not enough garden for GSHP horizontal (can't afford a borehole) - and too peaceful for an ASHP (we can hear shrews rustling in the garden)....

Our fabric is sufficiently well insulated to meet UK Bldg Regs SAP by using an oil boiler for CH & DHW (Calor won't fit me an LPG tank - not enough space to qualify with "safe" space separations) - hence we have ended up with the oil boiler option.

Our heat loss calcs I completed show about 4kW. Smallest A rated boiler I can see is 15-21kW. It may well be much over-capacity for the small CH demand. But I guess needed for the DHW demand through a 200 litre cylinder. i.e. the DHW demand far outweighs the CH demand. Has anyone else experience of this? - and novel or smart solutions?

Also - now I know the fabric heat loss (which is nice and low for a 220 sq.m house) - how should I sensibly size radiators to meet this? I was thinking of just using a rounded rule of thumb and adding say 1.5kW in the main sedentary lounge/diner/kitchen biggest room and 0.5kW per room thereafter. That would add up to about 7.5kW of radiators around the house. Does that sound about right...!

Many thanks in advance for your comments and opinions - cheers - LAS

Which hot water cylinder?

XT600 — Wed, 17 Oct 2018 20:26:15 +0100

I need, I think, a vented indirect cylinder with two immersion heaters.
Currently, I'm running a gas combi boiler but because it's almost new I don't want to change it.
I'm adding another bathroom to my property, and extra solar panels (on top of my existing grid tied system) to make use of roof space. I plan to install a 200 ish liter tank, with a heating coil heated from the existing combi (tapped into the central heating circuit?)
I plan to have the option of diverting unused solar electricity to one of the immersion heaters, and make use of another 12/24v immersion heater connected to my 'extra' solar panels.
I also want the option of being able to heat the tank via the combi boiler when necessary.
I want the whole system to be fed from a cold water storage tank in my roofspace, which can in turn be filled with water from my borehole rather than mains supply.
Does anyone see any problems with this arrangement, other than the fact that I'm not sure the tank I will need even exists? :cry:

DIY Header Tank

ComeOnPilgrim — Sun, 12 Mar 2017 10:29:11 +0000

I need a funny shaped header tank for a vented system. It will probably have to be long and thin to fit in the space below the ridge of the roof. How feasible is it to build one? I was thinking of asking a fabricator to build a box out of stainless steel. Is it straightforward to make copper connections to the box?

The other query was insulating it. It should not get too hot, but it would be sensible to have some insulation. I've seen these spray on foam companies. Might this work? Might there be a better solution?

I'd be grateful for any comments!

smallest stove possible....

Carol hunter — Tue, 18 Sep 2018 11:30:30 +0100

Dear Illustrious Community,

building a lovely round strawbale hut for my therapy practice.....It's 3m diameter and quite low in height, 2020mm?
Needless to say not with building regs.

Would like a very small wood stove in case of cold weather. Quite well oriented solar wise but shaded by near leafy walnut trees. We've had a Windy Smithy "Wendy" at 2.5kw in our 2 berth caravan which is overkill in that...so looking for smaller! Of course the mass is the important part as a twig burner will require attention and go out frequently/not store heat.

A few years ago there was a lovely design in Permaculture mag for a DIY brick built mass heater (kachelofen style but small). Does anyone know of any nice plans for a really small mass type wood/biomass burner built with bricks or the like or have any pointers? Everything is likely too much and I'm a hot middle aged woman....ahem.....

Heat Pump and Thermal Store combination

adrian hollister — Tue, 03 Apr 2007 01:13:26 +0100

Following some of the comments on my coal discussion thread, I've been looking at alternative ways to change to a renewable energy source. I've given up with wood pellets, getting the 'stove' type appliances is just too difficult (and therefore risky for support and maintenance) and have found a nice source of wood that I intend to use on my multifuel stove - though I may keep a little some coal going :confused:

So in a wave of new thinking, I've looked at alternatives and would like to consider using three heat sources for my hot water and central heating (using a thermal store)... the multifuel stove for heat top-up; solar panels vertically mounted on a south facing wall for spring/autumn heating boost; and a ground source heat pump. I've found some nice solar panels that could do the job though I'm tempted to have a go myself and make something. I can also connect up the multifuel stove using temperature sensors and a pump (i.e. change from gravity feed to powered feed).

I've UFH downstairs and rad's upstairs, so it's a great combination that I intend to use as 'ufh heating on three seasons' and 'radiators on when very cold'.

The thing I'm having a problem with is two fold..

1. None of the heat pump resellers/manufacturers that I've spoken to recommend a thermal store (except Worcester, but their output and price is just too excessive for me). I like the technology by the manufacturer based in Cornwall (and the local production), but they actively discourage the use of thermal stores on their site, but don't give any real details of why. I'm only looking at a bottom of the range 1kw input heat pump that can run off-peak. Is there a real reason why I can't use heat pump's with thermal stores?

2. None of the major thermal store manufacturers offer options for three 'input' heat sources. Do I just run the heat pump and multifuel stove off the heating ring? Anyone have any recommendations?

GSHP DIY control. Existing Software redundant

janoska666 — Thu, 13 Sep 2018 16:27:25 +0100

Hi Folks, i hope all is well. I have a premier 3 phase GSHP with a gas filled ground loop for a collector. Its from an Austrian manufacturer who have gone bust and taken over by another outfit. The hardware the pump end is excellent.
The controls and electronics is rubbish, over complicated and many issues with data lines and fault codes etc. Reset, reset etc. Web connected totally insecure and constant patches to keep it running and safe.

The new manufacturer is unable to fix other than change the controller, the control panel and the main pump control unit. Total cost 1700 quid with no guaranteed fix. Insane. Bit like fixing a new car, change everything and hope for the best.

Does anybody have a an idea or recommendation to use a simple control unit for the house side of things.

Very simple, DHW to 55 degrees.....1000 litre tank...... tank reaches 55 degrees..... 3 way valve to open and send the hot Heat pump water to a simple existing UFH heating setup.... run the UFH pump constant with a mixing valve and constant 7 degrees diff T...... KTY sensors and normal wilo pumps.

The pump side of things can be jury rigged. High gas pressure , Low gas pressure and flow temp to shutdown pump and turn on a simple fault light on a simple house controller.

I have considered Arduino and technis alternative. Good gear and service with software support etc.
see https://www.ta.co.at/en/freely-programmable/rsm610/

Simplicity, robustness and future proof controls essential.

Any ideas or pointers appreciated.

Growing citrus in the snow

dereke — Mon, 03 Sep 2018 17:07:52 +0100

Check this out - these people are growing citrus in Nebraska with pretty impressive results. https://www.youtube.com/watch?v=ZD_3_gsgsnk

They have pipes going under the ground that the blow air through and use the heat from that in winter to warm the green house and the cool for cooling in summer.

I'm a bit surprised they get enough heat out of it to keep the temperature stable but hey they are doing it and it seems work. What I am interested in is whether a similar thing would be possible to supplement an ASHP for a house. I've read all the stories about them freezing up in winter and having to run defrost cycles and the COP dropping off. Surely this would be a better source of air. I imagine it is much cheaper to install as well (I was recently quoted Â£10k for ASHP vs Â£20k for GSHP).

What do you all think?

Do Air to Air heat pumps have higher COPs than Air to Water or Ground Source systems?

GarethC — Mon, 22 Apr 2013 15:06:33 +0100

In practise, compared to Air to Water and Ground Source heat pump systems, are Air to Air heat pump systems a) (most importantly) more efficient for domestic heating and b) cheaper to install?

I think they should be, making them perhaps the best renewable heat solution, but I can find no research to confirm or refute these propositions. Can anyone help? More background below.

-----------------------------------------------------------------------------

The Energy Saving Trust field trial found that A2W heat pumps average system efficiencies of 2.2 (3.2 at best). Ground Source manages 2.4 (high of 3.3). Thatâ€™s too low to be worthwhile vs. most other heating sources, and nowhere near vs. gas. You need 3.0+ to be better (for cost and carbon) than a high efficiency gas boiler.

And A2W and GS are very expensive to install. You are looking at Â£8k for A2W and Â£13k for GS.

So you pay a fortune to install something dirtier and more expensive to run (not to mention service) than gas. You can generate your electricity greenly, or pay for ecotricity, but your heating costs will be even higher.

Now, as far as I can tell, A2A should have the following advantages over A2W and GS, leading to significantly higher COPs:

1. Fewer heat transfer stages (ambient heat to refrigerant, then refrigerant back to air). A2W & GS have: ambient heat to refrigerant, refrigerant to water, water back to air via big radiators or underfloor heating.

2. Lower required output temperatures: A2A will pump directly to heat a room to 20 degrees. A2W or GS have to heat water to much higher temperatures. The larger difference between ambient and output temperatures will make it harder for the system.

3. More direct and efficient transfer of heat to internal air. With A2A refrigerant heat is transferred back to convected air in internal wall unit. A2W & GS use big radiators or underfloor heating and natural convection. I believe this the latter will be a less efficient means to transfer heat where it is needed, with greater heat losses.

4. Less heat lost to sub structure. Air to air will blow heated air straight into the room. Radiators tend to heat the wall behind them, and underfloor must heat the floor substrate, with some lost around the ends and in the pipes between the radiators and hot water tank.

5. Faster heating. Not really an efficiency point in itself, but A2A will start pumping forced convection hot air quickly. A2W/GS will take time for radiators to heat, and once they do, will rely only on natural, not forced, convection, so take much longer to heat spaces. This means:

6. No unnecessary heating: A2A can come on when required (or just before when required) if they will heat space faster, and only heat rooms where internal units are switched on (i.e. where they are needed). A2W and GS will have to heat water in the tank even if it will not be used for some rooms (otherwise it would take forever for the water tank to heat, then for that water to heat the radiators, then for the radiators to heat the room). Additionally, some heat will be lost as the water sits in the tank.

Disadvantages:
1. Air to Air internal units will use electricity, lowering the overall efficiency. But from what I can tell, this shouldnâ€™t be much. Can anyone confirm this?

If the above factors (or some of them) are correct (and ignoring downsides such as internal noise for the moment), the real world COP and system efficiency of an A2A system should be significantly higher than A2W and GS. If A2A manages efficiencies of over 3 (and manufacturersâ€™ ratings can be 4-5), then it is much better than the alternatives, and cheaper and greener even than natural gas (you might even pay for expensive green electricity and go carbon neutral, without it costing more than natural gas).

Moreover, an A2A system with 6 indoor units should cost Â£4.5k to buy and install. Thatâ€™s 56% of the cost of A2W and 35% of GSH, and frankly much nearer to what people can afford. Add this in, and you have a system which is much cheaper to install AND run than A2W/GS.

Itâ€™s what Iâ€™m inclined to go for, but hereâ€™s my problem. I canâ€™t find research which will confirm or refute my propositions above. The EST field trial only looked at A2W and GS, and they have no plans to look at A2A. If Iâ€™m correct about A2A being more efficient AND much cheaper to install, the lack of definitive research on this will cause the system to languish when it could be the holy grail of renewable heating. Moreover, Iâ€™d really like to know if what Iâ€™m going to go for is silly or not. Does anyone know of any research on this question, or have observations on whether they think I am likely to be correct or not?

P.S. I have deliberately ignored domestic hot water. I know A2A wonâ€™t do this, but space heating is 75% of total domestic heating energy requirements. If I can get my head around the real world COPs of A2A for heating, I was then going to consider how best to â€˜add inâ€™ hot water. It might be best to have an alternative heat source for water (LPG, gas, electric, solar thermal etc.) or to use a heat pump to pre-heat water to a combi or something. Probably a â€˜follow upâ€™ topic.

Solar DHW cylinder recomendations

philedge — Sun, 19 Aug 2018 21:36:05 +0100

Im looking to replace our twin linked 120 ltr DHW cylinders with a new single cylinder. New cylinder will need a solar thermal coil, a gravity coil for a nearby wood burner and a third coil for a pumped boiler circuit. Looking for around 250ltrs capacity.

Anyone recomend quality suppliers that stock/ build this spec cylinder??

Combining UFH and Rads with Heat Store

ComeOnPilgrim — Tue, 27 Mar 2018 17:32:36 +0100

We have a large open-vented heat store in our loft with 3 spare ports (top, middle, bottom) heated by solar thermal and stove. It seems to work fine. We'd like to combine it with ground floor UFH and first and second floor radiators (see diagram). I'm wondering about the best way to connect and control these different temperature outputs. Would anybody be able to give me any pointers? I'd be very grateful.

(I also buried some temperature probes in each UFH zone in the screed. I haven't wired these up to see if they work, but I thought it might give us an option.)

Smoke Nuisance â€“ is wood wood?

Mikeee5 — Sat, 07 Jul 2012 12:23:45 +0100

Welcome to the thread. It's quite a read but to cut a long story short, wood was wood, smoke was smoke and a happy end to my saga was ..........

Re-using plastics for insulation....?

Carol hunter — Sun, 29 Jul 2018 09:21:00 +0100

Dear Estimable Folks,

We're on our third strawbale building at our place, a very small round house to be my therapy/writing hut....
since this doesn't have dwelling status, we're wondering about the pros and cons of filling our twin plinth wall which will support the bales with bubble wrap/plastic bottles and the like. Can't see why moisture should be any more of a problem than using some sort of polystyrene based material....Of course the ideal would be maxit/leca/hasopor but money is short and unwanted plastics more than plentiful....
Your responses would be most welcome.

CH pipes and maintaining joist integrity

andyman99 — Tue, 24 Jul 2018 16:14:47 +0100

I need to notch lower floor joists for 22mm CH pipes. These will go beyond the permitted depth, my joists are only 4" deep. I've found these

https://www.mytub.co.uk/yorks-22mm-double-pipe-joist-clip-product-329121

Do they look suitable to maintain joist integrity? Or does anyone know of other (cheeper!) options?

Recommendations for heating system upgrade

Sprocket — Tue, 24 Jul 2018 09:57:14 +0100

A friend has a big detached house. Pretty well sealed, modern glazing, reasonably insulated etc.
But it has all electric UFH set in deep (8" plus) screed. It's on economy-7 but even so it's not exactly cheap to run or convenient or easily controllable since there is huge lag.

Taking up the floors to re-do the heating sounds a lot of trouble and cost.
He is wondering about adding air source heat pump(s) and warm air heating (eg. like fan coil).

Any helpful suggestions or ideas?
And should we be looking for a a good renewable consultant to advise and design?

Don't want to fall foul of advertising rules in here so if anyone has specific consultant recommendations (in South West, near Bristol) then feel free to whisper comments with names too.

Thanks

Fan assisted spur on MVHR

johnuready — Sat, 14 Jul 2018 08:56:47 +0100

My passive bungalow works extremely well but as the utility room is in the centre of the property it can get too warm. The utility room has the MVHR, PV inverter, hot water tanks and all the bits of electronics that manage and control the property. I was thinking that I could spur into MVHR pipe to the outside world and extract heat directly from the utility room with an extraction fan that is thermostat controlled

Anybody have any ideas or solved direct extraction in a passive building?

Insulation round flue through a pitched ceiling

nprior — Thu, 12 Jul 2018 18:15:51 +0100

We are having a new stove and flue installed in a room with a full height pitched ceiling ie the flue exits from the room directly to the outside through the roof. Clearly we have to have suitable clearance all round the flue to anything combustible. This then leaves us with a minimum 50mm gap around the flue pipe with only the roof flashing between us and all the cold air outside.

Having spent much time in our original build preventing our builder from punching holes in the envelope at will, I'm reluctant to end up with such a large hole in the roof (from a thermal point of view anyway).

Stove installers I have spoken to have been fairly insistent that they would not normally fill the resulting cavity in the roof with anything, not even nonflammable insulation. Reasons vary from "never done it" to "you'll see the insulation poking through the trim plate". My guess is they haven't had to think too hard about air tightness but I may be maligning them.....

So: can we just stuff a load of nonflammable insulation wool round the flue in the hole through the roof? If so what would you recommend we use? If not, why not?

(Exiting through the wall is no better option - timber frame)

Oil fired boiler replacement - options ?

zak99 — Fri, 06 Jul 2018 00:31:29 +0100

Hopefully soon embarking on some improvements in our (I guess 70's) brick n block cavity detached bungalow, including window upgrades, some external insulation etc.

Our boiler is a really old oil fired worcester danesmoor, it works fine but is noisy. The radiators are quite old but in good condition, pipework is in the concrete floor. We also have a wood/coal stove. Theres no gas supply in our village.

What options for replacement should I be looking at please?

Small, reliable MVHR unit

runcyclexcski — Tue, 26 Jun 2018 19:11:40 +0100

Hi all,

I am after a small, reliable, air-to-air heat recovery unit. Actually, this would be a cold-recovery unit, as this is for a walk-in fridge room which needs a dessicator dehumidifier (I get black mould otherwise, humidity is constantly at >94%, tested with a probe). The room is only 10 square meters, ceiling 2 meters high.

I looked for heat-recovery units, but they seem quite expensive, considering that they are merely interconnected pockets of foil, 4 ducts, and (at best) two fans. However, I also found these:

https://www.ebay.co.uk/itm/SAHRU150-Passive-Heat-Recovery-Unit-Low-Cost-Whole-House-Ventilation/

Is there anything wrong with Sahru units? I intend to keep it always-on 24-7-365. If not a good idea, can you recommend a small, but robust, ducted MVHR (say, <150 cubic meters per hr). Fans are optional, as I can add on my own.

Wet UFH on earth floor with minimal insulation

jemhayward — Sat, 31 Mar 2018 09:38:07 +0100

We have a 16c house with a stone vaulted cellar. We are currently working to minimise water ingress, but we are limited by practicality, and the fact it's grade 2 listed. The floor is random stone flags, then soil. We have to temporarily lift the flags to dry the floor out as much as we can, but when it goes back down we'd like to drop the floor level slightly, possibly install a radon barrier, and improve the drainage for when water does get in. I feel we need to accept the probability that the cellar will flood at one pont in the future. We have an ASHP that has plenty of spare capacity, so we're thinking about under floor heating, but we won't have room for any significant amount of insulation. We also feel the floor should be breathable (despite the theoretical radon risk). Could we look at the earth floor as some form of thermal store, or will we be wasting half our heating bill heating up the countryside with no benefit to the occupants?
Anyone with any experience or recommendations?

Blowing hot and cold

tony — Wed, 16 May 2018 08:31:23 +0100

Yesterday I happened to visit some offices to help with sustainability. What I saw was quite remarkable.

The air cooling system was on and some areas were a bit too cool I reckoned, so did some of the staff as they had fan heaters on trying to warm their area up a bit.

How common is this, I have seen this in winter with the heating on but never before in summer.

Thermal Store System Check

Bowman — Wed, 27 Jun 2018 12:03:39 +0100

Just looking for a sanity check before I push the go button.

Super insulated renovation, family of four, no mains gas, no space for oil or LPG tank, currently E7

Planned system due to cost is:

Stage 1.
Newark thermal store - 300l, 2 x immersion, heat pump coil, either PHX or DHW coil?

Stage 2.

UFH downstairs and upstairs on separate loops.
12kW ASHP (FIT) into bottom of store

Any thoughts appreciated.

No Gas - general stratergy

goodevans — Sun, 06 May 2018 14:40:50 +0100

Due to various issues with tree protection and mains gas lines not adoptable by Cadent if laid in a duct I may well not end up with gas in our new build. Assuming this is the case I have to rethink my DHW and space heating plan.

On the plus side - no gas boiler and no gas supply charges (say Â£5000) and no standing charge (say Â£90 per year).
On the negative side no access to energy at around 3.5 p/kWh.

I calculate the house will have a heat loss (inc, ventilation and infiltration) of around 140W/K - that will give a peak heating demand of around 3000kW. (location UK, Cambridgeshire)

There will be two occupants 99% of the time, no baths, but the DHW should be designed to cope with visitors so 6 people in total. The house will be occupied most of the time.

I can site 2.5kW solar in an OK position if necessary (about 20 degrees south of east on a 40 degree pitch).

Cost is the main factor here - we do not have an unlimited budget so a balance between capital and ongoing costs is a factor.

At the moment UFH and ASHP seems like the space heating of choice for this situation (correct me if there are other solutions) - and it looks like an 8kW Ecodan will do the job.

But what about DHW. I'm prepared to implement almost any solution - from tank-less/on demand electric heated water everywhere, or, at the other extreme, a small TS with ASHP and solar PV assist with an inline electric boost or other fancy system. Which way would you go/have gone?

Smoke Nuisance from neighbours chimney

Waddler — Sat, 23 Apr 2016 20:15:56 +0100

I am so glad I have found this forum, I was starting to give up hope.

We are in the same situation with a neighbour's smoke. Their smoke never seems to go away, most of the time it comes horizontal out of the chimney then drops straight to the ground. If the wind is in our direction it comes straight over to us hits our house and then sits in our garden comes into our kitchen and conservatory, we can't even sit out on the patio at times because the smoke is so strong it burns the back of your throat.

There is a height difference in houses, our house is 4 storey and on a slightly higher level to the neighbour, their chimney is about the height of our downstairs windows, so our house is a huge barrier for the smoke to hit, there are also alot or large 15+ metre high trees around, the pressure seems to be downwards that the smoke never leaves the area.

We have a neighbour who has the attitude of 'I'll do what I want and I don't care if affects you'. Unfortunately there are no other properties around it is just us against him.

The problem has been going on for 2 years so far, the first year we did not say anything and hoped that he would look into the problem as he said that he was having draw issues with his chimneys. The second year reported it to env health, who took nearly 6 months to send a diary, eventually they wrote him a letter to inform him of the complaint and asked him if he was burning the correct fuel. The neighbour changed the cowl on the chimney which has made no difference at all. Just complained to Env health again as the smell has become really acrid, even standing in our garden for a few mins gave a burning sensation at the back of your throat. Env Health don't seem to want to know, he said unless he can see the smoke particles coming in our house through the windows he can not put it down as a complaint, does not matter that we can not sit in our conservatory, patio area or kitchen with the acrid smell of the smoke. The other problem we have is that every time we phone him to say it is happening, he can't make it out or turns up 4 hours later when it has died down.

The neighbours have a woodburning cooker that is connected to a thermal store so we don't even get a break in the summer as it is going all the time, sometimes from 8am to 10pm. What makes it worse is that the summer is coming up and you want to open your windows but you know your house is going to get full of smoke.

I'm still reading through the whole of the thread, but we can't live like this and we could never sell the house with this problem so we're digging our heels in and going to fight to get it sorted out, I know it is going to be a long hard slog.

Supplementary heat source or Replace log-gasification boiler?

jrw — Sat, 28 Apr 2018 16:21:34 +0100

Hello All
Long-time reader, first time posting here - I have looked at numerous related posts on the forum but I would really appreciate some informed opinion on my specific situation.

I currently have a 45kW biomass boiler (logs) heating a 2,500L thermal store, which heats my radiators and DHW cylinder. Due to a change in circumstances I am not consistently around to shift logs, feed the fire, clean it out, etc. So I need to install another heating system, either to replace the biomass system entirely or to add heat to the thermal store when I am not around to get/keep the fire going.

Option 1
Bin the biomass boiler and thermal store and install oil.
Option 2
Keep the biomass and thermal store, but add oil/ashp/gshp heating the thermal store.

I don't want to go for oil, but I know that the heat pump options will not give me the temperatures for my DHW and radiators. But might they be sufficient for 9 months of the year (I am in South West Wales), with boost from the biomass required when it gets properly cold?

To complicate the situation, I am also looking at a 6kW solar PV system which could divert excess power to an immersion heater in the DHW and/or thermal store. Does anyone have any experience of the real-world benefits of this set-up?

Thanks

rooftop solar assisted heat pump

toddm — Thu, 15 Mar 2018 16:14:46 +0000

Hi. American here -- a lonely advocate for multifuel central heat on this side of the Atlantic. At present I have a Stratford Ecoboiler heating a 750L vented storage tank. The storage heats underfloor radiant on thermostats. I also have a 24-tube pressurized solar system heating a 300-liter dual-coil tank, and a drainback loop that ties the two tanks together.

My next project is to integrate an air-to-water heat pump. Because the solar tank coils are undersized for heat pumps, the ATW unit will heat the large tank through a flatplate heat exchanger.

My question: how do I connect the solar system in series with the heat pump, using preheat to gain COP, while preserving its original loop for summer use when the heat pump is idle and the main storage tank is cold? The best I can think of is to wye solar to the entry water pipe adjacent to the heat pump, using a a back flow preventer in the flatplate pipe to prevent reversal when the pump isn't running, and wye it again on the hot side with another BF preventer blocking reversalon that side of the flatplate loop. The solar pump is downstream of the heat pump, drawing coolant through it. The solar system has a heat dump radiator that kicks on at 60 degrees Celsius so it isn't likely to harm an idle heat pump. (I think.)

I might be overthinking this (my specialty.) In a parallel system, the heat pump still backs up domestic hot water because the tanks are linked. (That link also moots the question of whether the heat pump loop in operation would interfere with the the solar loop.) At any rate, your thoughts also on whether a series system is worth the trouble?

Automatic solar panel alignment, for domestic hot water

orangemannot — Mon, 23 Mar 2009 09:55:45 +0000

So there I was pondering whether to fit a Willis Solasyphon ( at Â£305.00 + Vat) or an additional 250 litre solar hot cylinder ( at Â£400.00 + Vat) in the roofspace.
And commented to Senior Managment that I would probably go with the evacuated tube system.
Denise, being an Astro Physist, immediately commented that the panels should track the Sun, and indeed be ground mounted for optimium orientation. Though the amount of plumbing would surely render this impractical
Is there any such a system, for roof mounting, with a two panel set up and modern microelectronics surely this should be reliable and affordable?
jat
M

Bosch Compress 4000 2.0 EW MVHR and radiator valves

pdurkan@yahoo.co.uk — Mon, 02 Apr 2018 17:02:16 +0100

Hi,

Maybe a bit of an obscure question, We have a new one of the above. The installers have advised us that all the thermostatic radiator valves must be fully open all the time so the unit can work at highest efficiency, and so that the compressor lasts longer.

Things become uncomfortable in many rooms, especially at night when one wishes a cooler temperature in the bedrooms. Plus, this advice seems to somewhat defeat the point of having thermostatic radiator valves.

Our house has no inner room thermostats, rather one outer thermostat situated under the eaves of a west-facing wall - this is a common set-up here in Sweden.

Does anyone know if the installer's advice is correct? The Bosch manual says that we can turn down thermostatic valves as we wish, so we're awfully confused.

Thanks

Small air-source heat pumps for low energy houses (with/without creative hacks).

TimSmall — Fri, 02 Feb 2018 14:57:40 +0000

Does anyone know of a cheap ASHP ("air to water") with an output in the region of 3 kW or so? I've looked but can't find one.

The irritating thing is that you can buy 2.5 kW to 3.5 kW heat output mini-split ASHPs with SCOPs of 5 or better (the new-ish R32 units from Mitsubishi and Daikin) for about Â£700 to Â£1000, but they're all sold with a single indoor unit (the wall-mounted indoor unit houses a refrigerant-to-air heat exchanger with a fan, plus some controls electronics, but no more than that).

If you want air to water heat pumps, you're quickly into the Â£3500+ zone for larger units with lower SCOPs (which use the less efficient, but higher GWP R410a refrigerant).

If you are feeling adventurous it's possible to convert these sub Â£1000 units into "air-to-water" heat pumps. To do this, you substitute the whole indoor unit with a refrigerant-to-water flat plate heat exchanger (available for around Â£100), with some adaptation to or replacement of the indoor unit's electronics to keep the outdoor unit happy. In the UK this would need an "F-Gas" certification, and I suspect any warranty claims might be tricky...

Another approach I've found people using is to buy a second-hand de-gassed older generation mini-split (R22 or R410a based) for circa Â£100 to Â£200, carry out the above air-to-water modification and then charge it with propane (R290) - which has a very low global warming potential, so doesn't need F-Gas certification.

Since propane is flammable, you'd want to keep it outdoors by putting the flat-plate exchanger outdoors (much like the Mitsubishi Ecodan and other commercial heat pumps do anyway).

To add to the list of creative heat pump hacks that google has turned up, I also found a few examples of people converting small ASHPs to be hybrid air-source and ground-source heat pumps, by adding a small ground loop to bump up the COP. In heating mode the evaporated refrigerant passes through the refrigerant to air heat exchanger as usual, and then goes through a second refrigerant to water exchanger (the water then passing through the ground loop).

This has the advantage of needing a fraction of the ground works of a conventional GSHP (to the extent that for a small unit, you can make do with throwing in some plastic pipe when you're trenching for drains and telecoms etc. anyway), and that you can automatically turn off the ground part when the air temperature is higher than the ground temperature (e.g. spring/summer).

Perhaps it's better to wait for the 5 kW Mitsubishi Ecodan to come out in a higher-efficiency R32 version, and then wait a couple more years for them to come onto the second hand market - after some new-build houses fit Ecodans only to have the occupants later change them out for bigger gas boilers because they can't cope with the actual heating load...