Jump to content

Design and cost of hot water heating system


volcane
 Share

Recommended Posts

Hi All,

 

We are eventually beginning to make real progress on our new house (after 2+ years in planning)

 

The site has been cleared, layers of stone installed and the Kore ESP for the foundation has been delivered. The ESP will be laid next week with the required ducts and drainage installed ready for the slab to be poured. (the frame, a SIPS with cellulose is 80% complete and the windows and doors have been ordered). We are aiming for passive levels of insulation and airtightness, South facing un-shaded. No stoves.

 

Our house is large approx 400sqm plus double attached garage. 5 bed with 2 ensuite, a main bathroom, additional shower room and a small WC. So 5 showers, 1 bath (young children so currently 1 bath per day). Shower use 3 per day. Occasional guests so need capacity for that.

 

So we should need very little heat and could likely do without bar a few small electric heaters but we will put in UFH pipes (in the grand scheme of things this is a very low cost).

 

But what do we do to provide the small amount of heat to the UFH and more importantly heat our DHW? and how much is it likely to cost both to install and to run?

 

Options under consideration:

 

Mono block ASHP + UVC (perhaps 400 litre) issues legionella

Split ASHP + Sunamp stack (6X2)

LPG gas boiler with UVC (and buffer for UFH)

 

We are in Northern Ireland so no RHI and PV is no longer cost effective (vs E7 electricity)

 

A gas boiler is likely to have the lowest capital cost and should be good for 20 years, I'm not sure how long an ASHP would last, long enough to justify its cost?

I'm attracted to the Sunamp system but it is very 'capital heavy' and if the ASHP fails or needs expensive maintenance then I would be better just going with a gas boiler, but the Sunamp would be better placed to accept PV input if they become cost effective.

 

 

All opinions welcome,

 

 

 

Link to comment
Share on other sites

The legionella issue with ASHP is easily solved with either one or two immersions on a weekly timer set to 65c

 

I am looking at using a 250 UVC with a nightly E7 boost to 65c to make the most of early morning reduced rate whilst the ASHP is bringing the buffer and floor up to temperature. 

 

Your other option is a DHW UVC at a smaller size and then use the ASHP to heat a buffer tank at 35c - use it for both floor buffer and DHW pre-heat and the ASHP will be at its optimum CoP

 

ASHP has been around long enough now that there are plenty of installers and maintenance is simple. The other benefit of  all electric is that you can heat the tanks (albeit a little expensive...) using electric if the ASHP packs up

Link to comment
Share on other sites

As a guide to longevity, Panasonic in the past has offered a 7 year warranty on ASHPs installed by certified Panasonic installers.  Not many appliances give you that sort of warranty, and I think it gives some idea of what they expect from their kit in terms of longevity.

 

ASHPs are basically large fridges.  There aren't that many moving parts, and they've been around so long that the engineering is generally pretty robust.

 

We went for an ASHP, but that was largely driven by the lack of gas connection and our speculation that we'd need to cool the slab in summer.  That didn't really turn out to be the case in the end, as we just don't have that much solar gain.  Do consider UFH pipework in the slab though.  Running it for a least a few hours a day (especially when sunny) helps distribute heat evening around the slab.  I suspect our kitchen would be intolerably hot at times of the year without this.

Link to comment
Share on other sites

 I wonder if anyone who is using the UFH system for slab cooling can advise on any changes that are needed to the usual control system. I will be having a gas boiler, individual room stats and the usual UFH wiring centre. My (basic) understanding is that UFH pumps, room stats and boiler are all controlled via the wiring centre. If this is the case how can the circulating pumps be controlled / switched on without the boiler firing up.I would be grateful if anyone can point me to a wiring diagram showing this as I still have time to add any additional wiring that may be needed.

Link to comment
Share on other sites

Fairly simple that one - use a 3 channel timer, DHW is Ch1, Thermostat (Htg) on Ch2 and then the circ pump on Ch3 

 

You need to leave all the UFH circuits as open vented and then just wire the boiler "as normal" and use a spare connection to the circ pump  (9 is normally spare in a wiring centre on Y Plan) and then connect the Ch3 on to 9, L to the pump on 9 and wire back the neutrals. 

 

Create a separate programme for the circ pump (6am - 10pm etc) that is longer than the heating cycle and Roberts your mothers brother ... 

Link to comment
Share on other sites

38 minutes ago, Neil said:

individual room stats

 

Aahhh hang on ... you can't use the floor for cooling if you are using room stats and zoning. It's also fairly pointless trying to move the heat about from one room slab with solar gain to another if you want to control each room with a stat. 

 

Is this all ground floor ..? How large ..? 

Link to comment
Share on other sites

16 minutes ago, PeterW said:

 

Aahhh hang on ... you can't use the floor for cooling if you are using room stats and zoning. It's also fairly pointless trying to move the heat about from one room slab with solar gain to another if you want to control each room with a stat. 

 

Is this all ground floor ..? How large ..? 

Depending on manifold configuration it can be done,

Requires another stat (or multiples thereof) , set at the temp you want cooling to take effect, this simply opens (all) the manifolds and fires the pump/s , 

It all depends on how it's been plumbed though as to whether it can be made to work.

 

EDIT : usually also requires additional valves (sometimes) to shut off tank circulation,

 

Edited by Steptoe
Link to comment
Share on other sites

16 hours ago, volcane said:

5 bed with 2 ensuite, a main bathroom, additional shower room and a small WC. So 5 showers, 1 bath (young children so currently 1 bath per day). Shower use 3 per day. Occasional guests so need capacity for that

 

Discussion on which gas boiler here.

ASHP or oil here.

You may well have read them but they are still relevant.

 

As you imply, with five showers there are likely to be occasions when there will be a need for three or more concurrent showers, which means even the largest combi boiler won't be enough.

 

If you are considering the boiler option, I would recommend Vaillant's Choose a Boiler page - the guidelines that they give actually apply to all Boiler and cylinder manufacturers.

  • Like 1
Link to comment
Share on other sites

8 hours ago, Steptoe said:

Depending on manifold configuration it can be done,

Requires another stat (or multiples thereof) , set at the temp you want cooling to take effect, this simply opens (all) the manifolds and fires the pump/s , 

It all depends on how it's been plumbed though as to whether it can be made to work.

 

EDIT : usually also requires additional valves (sometimes) to shut off tank circulation,

 

 

That was my thought hence the query as to whether it is single or multiple zones. Issue with multiples are the zones are wired in parallel and any one zone firing for heat starts the boiler - the smart UFH wiring centres tend to have a relay in them that fires the boiler in this instance. 

 

I can't see a scenario where heating and cooling are needed in different zones but I'm assuming that you would need a lock out of some description although it would beg the question as to which zone has priority however what you're talking about here is more of a passive cooling effect by moving the heat from one place to another which needs open zones everywhere. 

 

I would simplify the design and lose the zone stats and the loop valves and use a single house circuit that gives you simpler control. 

 

 

Link to comment
Share on other sites

Given PH levels of airtightness and insulation, I think it's reasonable to assume that there'll be a short heating period during winter, and an occasional use for cooling during summer (depending on solar gain - we got through last year reasonably comfortably without cooling our house).  Between those, there'll be weeks, or more likely months, where the slab doesn't need to be heated or cooled.  

 

I'd therefore consider whether to make the system switchable between a summer mode and a winter mode.  Given you only need to switch it twice a year, a manual switch would be fine.  It might be as a simple as routing a call for <action> to either heating or cooling, depending on the switch setting.  

 

To be honest, you might not even need this given the way this sort of house reacts to changes in temperature over the year.  Set up properly, I can't see a situation where you'd be calling for (floor) heat and then wanting cooling within hours or even days of that.

  • Like 1
Link to comment
Share on other sites

Thanks for all the comments

 

I'm not overly concerned about heating as if the house performs as promised then we will need very little.

 

I'm concerned about running out of hot water and nuisance heat esp during the summer.

 

If possible i would like an option of being able to cool the slab.

 

Just on mobile

  • Like 1
Link to comment
Share on other sites

If you want to cool the slab, an ASHP is probably the only viable off-the-shelf option.  I suppose you could provide the wiring and plumbing for such a unit and decide after you'v lived with it for a while whether you actually need/want slab cooling.

 

In my experience, the only places that I've wanted cooling during the peak of summer is upstairs.  Downstairs was always perfectly comfortable, but after long hot spells the bedrooms did get warmer than desirable at times.

 

One thing I'd absolutely build in if I were doing this again is provision for insect screens on bedroom windows.  At times last year it was a choice between being too hot and being eaten by mosquitos.  

 

Another option would be a fan - I lived in Sydney for years, and found that a simple pedestal fan was fine to make the temperature tolerable enough for sleeping, even during very warm weather.

  • Like 1
Link to comment
Share on other sites

4 hours ago, PeterW said:

 

That was my thought hence the query as to whether it is single or multiple zones. Issue with multiples are the zones are wired in parallel and any one zone firing for heat starts the boiler - the smart UFH wiring centres tend to have a relay in them that fires the boiler in this instance. 

 

I can't see a scenario where heating and cooling are needed in different zones but I'm assuming that you would need a lock out of some description although it would beg the question as to which zone has priority however what you're talking about here is more of a passive cooling effect by moving the heat from one place to another which needs open zones everywhere. 

 

I would simplify the design and lose the zone stats and the loop valves and use a single house circuit that gives you simpler control. 

 

 

If you have multiple zones wired through a 'standard' ufh wiring centre, then 2 port valves can be used to close off separate zones for cooling,

By wiring centre I mean a proper proprietary type, not simply a box with a load of wires joined, if the latter, then you can configure the wiring any way you want, and the valves are often not required.

Link to comment
Share on other sites

Guest Alphonsox

Our "final" solution for our Northern Ireland passive spec build is as follows :-

1) DHW supplied by a Sunamp plus slave unit, electricity supplied by E7 only.

2) UFH supplied from a 90ltr buffer tank heated by 3kW immersion heater, E7 only.

3) Granny annex fan radiator supplied from the same 90Ltr tank.

 

I have put in place the piping required to fit an ASHP to heat the buffer tank if it turns out one is actually required. This is not currently connected to anything.

Cooling provision - None (be reasonable - It's Northern Ireland, just open the door)

 

We moved in a week ago and have found the heating to be almost redundant despite the cool evenings. I raised the slab to ~18C and it prtetty much stayed there with a quick blast of heat every night. The Sunamps have worked flawlessly and are worth every penny IMHO

 

EDIT :- The UFH is treated as one single zone with a single control valve  (Same as Jeremy's system). MVHR is not yet operational

Link to comment
Share on other sites

@Alphonsox

That's a lot of space heating from a simple 3kw immersion heater! You must have a proper smug grin with that result. :)

For the benefit of the thread could you elaborate on the 'slave' unit a little please ?

Congrats on moving in, and one assumes things will only get better when the heat recovery ( MVHR ) fires up ^_^

Link to comment
Share on other sites

Guest Alphonsox
3 hours ago, Nickfromwales said:

@Alphonsox

That's a lot of space heating from a simple 3kw immersion heater! You must have a proper smug grin with that result. :)

For the benefit of the thread could you elaborate on the 'slave' unit a little please ?

Congrats on moving in, and one assumes things will only get better when the heat recovery ( MVHR ) fires up ^_^

 

I have a smug grin and a befuddled plumber who was convinced I didn't have the slightest idea what I was doing and that a minimum 10kW heating system would be required. The big unknown is how the place will perform at the coldest times of the year. I'm sure I won't need more that 3kW but I may need to extend the "on" hours beyond the E7 period (wish we had E10 here).

For the record the standard SunampPV unit contains heat batteries along with a control system, heating element, pump and mixing valve. This unit provides around 140litres at 40C . They will sell you an expansion unit which contains just the heat batteries and connects as a slave to the main unit. This doubles the stored energy to a 280Ltr @ 40C equivalent. 

Link to comment
Share on other sites

3 minutes ago, Alphonsox said:

I have a smug grin and a befuddled plumber who was convinced I didn't have the slightest idea what I was doing and that a minimum 10kW heating system would be required. 

 

Ours was the same.  Point blank refused to accept that a 5kW ASHP would be sufficient.  He wanted to install a 14kW unit!  From memory, his concern was that the house temperature would drop during the couple of hours that the ASHP would be in DHW mode each morning, and that the ASHP would struggle to catch up with that loss as the day went on.

  • Like 1
Link to comment
Share on other sites

58 minutes ago, jack said:

Ours was the same.  Point blank refused to accept that a 5kW ASHP would be sufficient.  He wanted to install a 14kW unit!  From memory, his concern was that the house temperature would drop during the couple of hours that the ASHP would be in DHW mode each morning, and that the ASHP would struggle to catch up with that loss as the day went on.

 

I can't say much TBH, as I have received a proper education whilst residing with you lot :)

 

One of my mates rang me one day and said "I've had a job for a house with UFH. How much smaller should I make all the radiators?"? How we laughed.  

Link to comment
Share on other sites

24 minutes ago, Nickfromwales said:

One of my mates rang me one day and said "I've had a job for a house with UFH. How much smaller should I make all the radiators?" 

 

Well don't keep us in suspense, how much smaller should you make them when there's UFH? :D

Link to comment
Share on other sites

5 hours ago, jack said:

 

Ours was the same.  Point blank refused to accept that a 5kW ASHP would be sufficient.  He wanted to install a 14kW unit!  From memory, his concern was that the house temperature would drop during the couple of hours that the ASHP would be in DHW mode each morning, and that the ASHP would struggle to catch up with that loss as the day went on.

 

I'm using a 9Kw unit just because its what I purchased cheap ! We're not at passive spec either, but air tightness is key and we also have the MVHR.. If you time your DHW / Buffer / UFH correctly then nothing is fighting for heat anyway..!

  • Like 1
Link to comment
Share on other sites

On 24/04/2017 at 17:15, Alphonsox said:

 

I have a smug grin and a befuddled plumber who was convinced I didn't have the slightest idea what I was doing and that a minimum 10kW heating system would be required. The big unknown is how the place will perform at the coldest times of the year. I'm sure I won't need more that 3kW but I may need to extend the "on" hours beyond the E7 period (wish we had E10 here).

For the record the standard SunampPV unit contains heat batteries along with a control system, heating element, pump and mixing valve. This unit provides around 140litres at 40C . They will sell you an expansion unit which contains just the heat batteries and connects as a slave to the main unit. This doubles the stored energy to a 280Ltr @ 40C equivalent. 

 

@Alphonsox how many showers are you able to run con-currently from your set up? We have a lightly higher water requirement, with 2 adult showers 2 kid showers and a kiddie bath on average daily and then have guest capacity on top of that. Not running out of hot water is a SWMBO stipulation.

 

Our house is large (we got carried away) and is promised to be constructed to passive levels. We are fitting Internorm 3G windows so my main concern is hot water provision. Until the contribution by @JSHarris and others and knowledge of our last house where the utility was warmer than required then I would've went with an ASHP to an UVC.#

 

Is the Sunamp worth the considerable outlay to effectively store E7 electricty as heat energy and also deal with nuisance heat?

 

I'm looking at putting my PV budget into a Sunamp in order to make better use of E7 as PV panels aren't stacking up vs E7

 

Is there a monoblock high temperature heat pump that could work with the Sunamp? (in order to avoid using a split system)

 

And that then takes me to the control of my prospective set up!!

 

 

 

16-01 ASK-03 Elevations GFFF.pdf

Link to comment
Share on other sites

Guest Alphonsox

I don't currently have any feel for the concurrent operation of my Sunamp (We've only got a single bathroom operational). @TerryE had concerns over this and opted for a dual Sunamp system (two full units running in parallel feeding an external mixer) rather than the Single plus expansion set up that we have.

 

The Sunamps tick a lot of boxes for a passive build - Very low losses, small size, mains pressure water and as easy to control as an unvented cylinder. They are a bit more pricey but worth it in my view. With our Sunamp solution supplying up to 280Lts @ 40C we have found no need to switch on the electricity supply outside of the E7 charging window. In Northern Ireland we are paying around 7p per unit for E7 which is half the 14p standard rate. I don't have a feel for how much energy they are currently using but a quick back of the envelope calculation against PV goes as follows :-

A 4kW PV array in NI costs around £4500 to install and generates around 3300 kW/hrs/yr. This would save me £231 at E7 rates and would represent a payback period of around 20 years. In my opinion this makes PV uncompetitive from a cost point of view. 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...