The Optimum domestic hot water and heating system

[Triassic]

Over the last few weeks there’s been a number of threads about hot water and heating systems in highly insulated houses. I, along with others have followed and contributed to the conversation where we could. A few have said openly they are confused by the various options and the complexity of it all. 

 

So here’s a challenge for all these who’ve been through the DHW and UFH mill......

 

Please describe what a simple DHW and UFH system looks like, what components (the principle parts, ASHP, Thermal Store etc) you had in your system and why you chose these over other components/approaches?

 

The bottom line for me is to understand what an optimum system looks like.

[Nickfromwales]

6 minutes ago, Triassic said:

Over the last few weeks there’s been a number of threads about hot water and heating systems in highly insulated houses. I, along with others have followed and contributed to the conversation where we could. A few has said openly they are confused by the various options and the complexity of it all. 

 

So he’s a challenge for all these who’ve been through the DHW and UFH mill......

 

Please describe what a simple DHW and UFH system looks like, what components (the principle parts, ASHP, Thermal Store etc) you had in your system and why you chose these over other components/approaches?

 

The bottom line for me is to understand what an optimum system looks like.

Id put the kettle on if I were you  

 

Firstly, the least amount of kit. 

Secondly, the least amount of service / maintenance.

Thats a simple system.

 

@Stones has an ASHP direct to UFH and to an UVC which is reporting good numbers. Downside is the physical size and location of the equipment if you go ASHP > UVC so not great in a smaller or urban setting. Sometimes declined by planning. UVC requires annual G3 service and inspection.

 

@TerryE Has a willis heater direct to UFH and ( gulp ) 2x SAPV's for DHW. Almost zero footprint as the stuff would all fit in a large suitcase. To be honest the two SAPV's would now be replaced by a single eHw 9/58, removing all the pumps / flow switches etc so in essence they'd just be dumb boxes full of goo with no moving parts / valves etc at all. No G3 required so zero annual service, but inspection ( easily DIY ) still required. Nowt lasts forever without a bit of attention  

 

@JSHarris has an ASHP to a buffer > UFH, and that buffer offers uplift for the incoming cold mains. That feeds into a SAPV, same as above, could be further simplified by upgrading to an eHW SA unit.

 

If you want to add renewables it becomes a little more complicated, the maintenance becomes a bit more intense, and upwards of there tbh. 

As each instance is almost unique, its a very big question. You should really say "this is what I want to use, whats the easiest / simplest way of achieving it?"

 

The simplest system imo is grid gas > combi boiler > rads, or, combi > buffer > UFH. Both instances with instant constant DHW from the combi. 

 

 

[jack]

This is what mines looks like:

 

 

There are one or two more valves than what's shown, and the two filling loops (one inside, the other outside) aren't shown.

 

We went for an ASHP because we don't have gas, and wanted the ability to cool as well. (Incidentally, I enabled the cooling mode the day before yesterday for the first time, and was amazed at how quickly it had an impact. Now just need a way to cool the bedrooms.)

 

I went with an unvented cylinder because a thermal store would need to have been a lot bigger for the same effective capacity (ie, how much hot water you can get out), and we're a little tight on space in our plant room. If I were doing it again today, I might consider a thermal store (no need for G3 inspections) or perhaps a Sunamp if they do a unit(s) that's compatible with the rest of our system.  

 

It's pretty simple. The main annoyance is that the standard controller for the ASHP is dire. It's slow and counterintuitive to program. You can't program any logic into it (eg, once we leave the cooling season, I'll need to reprogram it for heating - not difficult, but 5 annoying mins trying to remember how the programming works). You can't even copy a day's settings to another day. Longer term I'd like to replace this with a more intuitive interface via our home automation system. 

 

 

[Pete]

19 minutes ago, jack said:

This is what mines looks like:

 

 

There are one or two more valves than what's shown, and the two filling loops (one inside, the other outside) aren't shown.

 

We went for an ASHP because we don't have gas, and wanted the ability to cool as well. (Incidentally, I enabled the cooling mode the day before yesterday for the first time, and was amazed at how quickly it had an impact. Now just need a way to cool the bedrooms.)

 

I went with an unvented cylinder because a thermal store would need to have been a lot bigger for the same effective capacity (ie, how much hot water you can get out), and we're a little tight on space in our plant room. If I were doing it again today, I might consider a thermal store (no need for G3 inspections) or perhaps a Sunamp if they do a unit(s) that's compatible with the rest of our system.  

 

It's pretty simple. The main annoyance is that the standard controller for the ASHP is dire. It's slow and counterintuitive to program. You can't program any logic into it (eg, once we leave the cooling season, I'll need to reprogram it for heating - not difficult, but 5 annoying mins trying to remember how the programming works). You can't even copy a day's settings to another day. Longer term I'd like to replace this with a more intuitive interface via our home automation system. 

 

 

Hi Jack. Interesting point that you make that one of the reasons you chose an ASHP was for the cooling aspect and yet you have only just used it in cooling mode for the first time when we have had all this hot weather for some time. Is that because you do not need to use the cooling mode as often as you thought? One of the reasons I ask is we have had a big delay in our build for one reason and another but we are now ready to move forward and we are at the stage of deciding on our DHW and heating choices. We have a near Passive build with solar coating on all South facing windows and I cannot stress how effective this is at preventing overheating in the house. With this in mind and the advancement in the Sunamp products we are leaning towards one of the new units with UFH and fit a small PV array and see if we can do without an ASHP for the cooling effect alone. The house had been shut up for a few days recently and was quite warm and I opened the door onto the roof terrace and a G/F door and the house cooled really quickly which was another reason to see how we get on when we have moved in. Our build has two bedrooms on the ground floor with only one upstairs which is off the roof terrace door so I can see it working quite well (I hope).

[Dreadnaught]

For a passive house, isn't the simplest and lowest maintenance the following…

• E7/E10. No gas, no PV*
• Sunamp for DHW
• electric UFH cables embedded throughout the slab (not just bathroom) for space heating

Big difference is no wet UFH. What's wrong with this?

 

* I have huge tree blocking the sun.

Edited July 10, 2018 by Dreadnaught

[Dreadnaught]

Oh, and if cooling is needed, first it shouldn't be much as it should be designed out at PHPP stage, but if it is needed then just install an £800 air-to-air split unit air-conditioner.  (I will put in place a conduit and wiring for one just in case.) 

Edited July 10, 2018 by Dreadnaught

[SteamyTea]

As usual, when talking about heating systems, there is a lot of bollocks spoken about the details.

 

There are two basic ways to heat DHW.  Directly when needed or heated and stored until needed.

Directly heated when needed requires a large boiler, the more hot water needed, the larger the boiler.

Stored until needed can use a much smaller output boiler, but it needs to run for longer to recharge the DHW cylinder.

All the rest, that nonsense about vented or unvented, large cylinders or thermal stores, thermostatic valves, heat exchangers etc is just the detail bollocks.

 

Similar with space heating in a way.  You can heat the air directly or heat some water, then pump it around the place to radiators  A radiator is really a convection heater, but an UFH systems is really just a large radiator.  The theory is the same e.g. how much power will it deliver.

All the rest is detail i.e. gas, oil, solid fuel, heat pumps, solar, PV.

 

What it really comes down to is how easy it is to install and how well you can insulate the parts that need insulating and place the parts that are hot.

 

One of the problems is that we have got used to combing and system gas boilers and most plumbers are only happy to use these.

They are not really that efficient, just that natural gas is so cheap that it looks that way.

 

But I think it is about time one of the plumbers did a few sketches of different wet heating systems and explained the differences between them.

Trouble is that prejudiced comes into it and to the unwary that can cause problems and confusion.

 

My view is keep it simple and split the space and DHW systems if possible.  One size does not fit all.

[jack]

48 minutes ago, Pete said:

Hi Jack. Interesting point that you make that one of the reasons you chose an ASHP was for the cooling aspect and yet you have only just used it in cooling mode for the first time when we have had all this hot weather for some time. Is that because you do not need to use the cooling mode as often as you thought? 

 

The main reason I've not bothered in the past is that downstairs (which is where the UFH circuits are) rarely gets so warm as to be uncomfortable. It's taken two weeks of unusually hot weather to get to this point, and that was the trigger to go and look up the code. 

 

My main concern is cooling upstairs, as that's definitely where it gets hot. Night purging works well, but in past years we've had real issue with mosquitoes getting in. It isn't so bad this year, possibly because it's been so dry(?) Insect screens would fix that, but to get the full effect of night purging, you also need to open blinds and curtains at least a bit, which means you get woken up by the sun really early in the morning.

 

We've also had a few nights recently where it's been very still, and where the temperature has only fallen into the teens for a few hours overnight. Purging hasn't worked very well in that scenario.

 

We have two windows that give us significant solar gain. One of those is a massive slider, and we have plans for a shade sail to significantly reduce sun during the hottest months of the year. The other is an east-facing window in our double height area. We plan to fit external blinds (already wired for and have a suitable recess) to that as we have on other east-, south- and west-facing windows. I expect that will improve things.

 

I also have a roof light that would be excellent for stack ventilation if only it would open. Another thing on the list of things that need fixing!

 

35 minutes ago, Dreadnaught said:

For a passive house, isn't the simplest and lowest maintenance the following…

 

In absolute terms, yes, probably. 

 

31 minutes ago, Dreadnaught said:

Oh, and if cooling is needed, first it shouldn't be much as it should be designed out at PHPP stage, but if it is needed then just install an £800 air-to-air split unit air-conditioner.  (I will put in place a conduit and wiring for one just in case.) 

 

I'm not sure whether it's possible to design out overheating in all scenarios, but yes, it should absolutely be minimised as much as possible.

 

And yes to air conditioning, although you need somewhere discreet for the inside unit(s). The natural place in our house would have been in the middle of the upstairs landing, where it would have stuck out like the dog's proverbials. 

 

Of more use, I think, is an inline duct cooler in the MVHR ducting driven by the ASHP to cool incoming air. Coupled with the cooling UFH, I'd hope that over the course of a summer's day you'd at least keep the worst of the heat under control, ready for night purging.

[PeterW]

Ok I’ll add this in. All electric with E7, above spec on airtight and uValues of 0.15/0.17 ish, ASHP is 9kw into a 250 litre UVC with 70 litre UFH buffer all run as W-Plan. 

 

ASHP set to max 45c on DHW with immersion boost overnight. UFH run at 30c, buffer 35c. 

 

Heating Schematic V2 2504.pdf

 

[ProDave]

1 hour ago, jack said:

It's pretty simple. The main annoyance is that the standard controller for the ASHP is dire. It's slow and counterintuitive to program. You can't program any logic into it (eg, once we leave the cooling season, I'll need to reprogram it for heating - not difficult, but 5 annoying mins trying to remember how the programming works). You can't even copy a day's settings to another day. Longer term I'd like to replace this with a more intuitive interface via our home automation system. 

 

 

This is my initial conclusion and in due course I will be looking to stitch a conventional heating programmer into the system so you can basically ignore the supplied programmer, and control it all from conventional straightforward heating controls.  There are one or two challenges for this but I have some ideas.  Watch my thread when I get around to doing it.

[jack]

9 minutes ago, ProDave said:

This is my initial conclusion and in due course I will be looking to stitch a conventional heating programmer into the system so you can basically ignore the supplied programmer, and control it all from conventional straightforward heating controls.  There are one or two challenges for this but I have some ideas.  Watch my thread when I get around to doing it.

 

I meant to mention, while looking through my ASHP's installation manual yesterday, I noticed that the default DHW run-time is 30 mins, just like you mentioned yours was (mine's a Panasonic Aquarea).

 

Custom control of mine should be fine, as I believe there are dry contacts allowing calls for heating, cooling and DHW. It's just a matter of making sure that the dry contacts can't accidentally be used to trigger an undesirable series of states (no idea what those might be, but things like minimum run times come to mind).

[Triassic]

3 hours ago, Nickfromwales said:

UVC requires annual G3 service and inspection.

So why not use a vented cylinder? What’s the problem?

Edited July 10, 2018 by Nickfromwales
Vented

[Jeremy Harris]

50 minutes ago, jack said:

Of more use, I think, is an inline duct cooler in the MVHR ducting driven by the ASHP to cool incoming air. Coupled with the cooling UFH, I'd hope that over the course of a summer's day you'd at least keep the worst of the heat under control, ready for night purging.

 

 

That's my next plan, @jack.  I'm working on it in my mind right now!  We have an external fresh air intake duct right above the ASHP, and it's a nuisance as the outer grill regularly gets clogged with fluffy weed seeds and cobwebs.  I have been planning for a long time to extend this down with an externally mounted duct so that it's turned through 90 degrees and so away from the wind that funnels all the fluffy stuff along the back of the house.  At the same time I was planning to fit an easily accessible pre-filter, to help keep the main intake filter in the MVHR a bit cleaner.  Last week I had the bright idea that it should be possible to fit a duct cooler in the same place as the pre-filter, and as that's only a few feet from the ASHP, I could easily plumb it to the existing connections, together with an electrically operated valve.  Even better is the fact that the cooling mode is already signalled out to the ASHP via a cable, so I could use that to trigger a circuit to turn the duct cooler on or off (it only wants to be on in cooling mode).

 

It would be simple to install, no need to mess around with drains, as I could run the condensate straight to the existing heat pump drain.  It would be around head height, so easy to work on, too.  It would more than double our existing MVHR cooling capacity, too, by cooling the incoming air to the MVHR (which by then would be at 100% bypass) to around 12 deg C.  If the MVHR heat pump was to also kick in, then I know that's capable of dropping the air temperature by around another 10 deg C, so we could have a pretty powerful way of cooling the upstairs rooms.

 

@Triassic, Sorry if this has gone off-track from the original topic, but getting back to that I think there is no one-size-fits-all option.  There are just too many variables.  You can say that you can design out overheating with PHPP - in fact you can't, really.  A few days where the air temperature is regularly in the high 20s, low 30s and even the best shaded passive house is going to start to warm up, especially with the warm nights we've had recently that have not allowed a night purge to be effective.

 

The location of the site will play a large part in the optimum system, as will the availability of gas.  If I had to plan for the future than I'd say we're probably going to need more summer cooling than we're used to.  I doubt that the weather over the past couple of weeks has been an anomaly, and suspect that periods of warm/hot weather may get more frequent.  Gas is clearly really good for heating and hot water, and far away the cheapest and simplest solution, particularly if a combi will meet your needs, but you then need to consider whether or not you want to use renewables, either for moral reasons or to reduce your energy bill.  A Sunamp will fit in front of a combi to provide pre-heat, or summer hot water, using excess PV generation, and makes a great deal of sense, but comes at a price. 

 

A heat pump is a more flexible source in many ways, as it's only slightly more expensive to run for heating than a combi boiler, but will provide cooling as well.  Combined with efficient heat storage (and without wishing to push a particular product, nothing comes close to the heat storage efficiency of a Sunamp - it's at least three times better than it's nearest rival, but again at a price) an ASHP can offer some significant advantages, mainly because it's not a one-trick-pony.  The ability to heat and cool is a very definite plus point, especially if you have PV, when the cooling will be free, as when you need cooling the sun is pretty much bound to be shining.

 

I think that the best approach may be to assess your site, and your house design, work out whether you can economically get gas or not, work out the heating and hot water demand, and have a stab at guessing whether some form of cooling system would be useful, and then work from there, bouncing ideas around on here.  When I started I didn't have the advantage of having many people around who had in-depth practical knowledge of low energy house heating and cooling options.  Now there are enough here that have been through the hurdles of putting systems together that I feel sure that going through the various design iterations for any house should be an easier process.  There are new systems coming on the market all the time though, so there will always be gaps in the knowledge here that you may need to work through.

 

From my personal perspective I would say that heating is a non-issue - it's so easy and relatively cheap to heat a well-insulated and airtight house that anything will do the job well enough.  Hot water is a challenge, as that remains the same as for any house, and a heat pump may or may not be great at delivering hot water efficiently - it depends very much on your hot water demand.  Cooling is very well worth considering, I think, especially if you're in a spot that's likely to get very hot for periods of time (like this past week).  Everyone will have a different take on things, though, so my priorities are certainly not going to be the same as those of others.

[joe90]

Well mine is like Peters above. We have no mains Gas (bottled gas for hob only because SWMBO demanded it ?) and without it I will save standing charges and maintenance. ASHP (cheap on Ebay), UFH downstairs only, towel radiators in bathrooms and electric UFH in our en suite. MVHR which I considered inline heaters (wet) for heating or cooling but can fit after if I find it’s needed. I am also considering E7 or E10 once we are in and see how the house reacts. Like Jeremy says, no two houses are the same, his site is not like mine, he is in a sheltered valley which is probably why he needs more cooling than heating, we are on flat ground a mile from the Atlantic so don’t think cooling will really be needed, but who knows? I didn’t do a PHPP frankly mine is guess work, let’s hope it works!

[jack]

41 minutes ago, Triassic said:

So why not use a ventilated cylinder? What’s the problem?

 

Vented either means gravity (=low pressure) or thermal store (=less available hot water for a given storage volume).

[Nickfromwales]

46 minutes ago, Triassic said:

So why not use a vented cylinder? What’s the problem?

No 'problem' other than the much higher standing losses from the tank, and the vent pipework to the CWS tank above it. 

Fwiw I would never spec an open pipe gravity hot water setup as your then quite restricted to what mixer outlets you can have as they'll need to deal with gravity hot and mains cold on basins for eg. Baths and showers can be balanced cold fed off the CWS if you double its capacity. 

[AliG]

Just as a piece of information. Due to the size of our house and for convenience we were recommended to use a circulating hot water system.

 

It is certainly convenient, you have hot water within seconds despite some fittings being almost 30m from the tank.

 

However, it is very expensive to run. It is on a timer and 3 times a day it pumps hot water round a roughly 60m circuit. This then sits in the circuit cooling down (and warming up the cold water which is nearby).

 

As the heating has been off for some time we continue to use a substantial amount of gas for hot water and I calculated that the heat loss in the hot water circuit probably runs to £100s a year ( actually I calculated it at about £2.50 a day if it ran constantly, probably about £1 a day for the amount we are running it), more than most people use for hot water all together. It is probably not helped by the builder not insulating the circuit. He deemed it unnecessary as they are all within the house. this might have helped but I think the heat loss would still be quite substantial.

 

Thus a consideration is to design your hot water system with the shortest runs possible. Our HW tank was at the opposite end of the house to the kitchen and master bedroom.

Edited July 10, 2018 by AliG

[Nickfromwales]

16 minutes ago, jack said:

 

Vented either means gravity (=low pressure) or thermal store (=less available hot water for a given storage volume).

You can have a vented TS with a DHW instantaneous coil inside it, commonly referred to as a combination tank. 

The telford Tri-store for one eg. 

[jack]

14 minutes ago, Nickfromwales said:

You can have a vented TS with a DHW instantaneous coil inside it, commonly referred to as a combination tank. 

The telford Tri-store for one eg. 

 

That's exactly the sort of thermal store I had in mind - the use of a coil means that you can't get as much water at a given temperature out as you will with standard unvented cylinder of the same volume.  Am I missing something? 

 

 

[Jeremy Harris]

28 minutes ago, Nickfromwales said:

You can have a vented TS with a DHW instantaneous coil inside it, commonly referred to as a combination tank. 

The telford Tri-store for one eg. 

 

 

That's exactly what I originally installed, but a double thickness insulation one supplied by Newark.  The heat losses were astronomical, at over 3 kWh/day, and that was with stipulating that the tank be double sprayed with foam from the factory.  I then added an insulating hexagonal box made from 50mm PIR foam around it, taping the joins and filling the gaps with expanding foam, to increase the insulation level further.  This got the losses down to around 2 kWh/day - still ludicrous, and way off the official figures using the BS test method (shades of the VW emissions scandal here).

 

I ended up tearing it out and selling it on ebay cheaply to get rid of it, and replacing it with a Sunamp PV, that has losses of around 0.6 kWh/day, far more sensible.

 

Bear in mind that a shower will typically be around 2 kWh or so, and we have two showers a day, so the original thermal store heat loss was equivalent to 1 1/2 showers a day...

[joe90]

We installed a 300litre Telford cylinder (care of Nick?) and I have to say we can feel almost no heat escaping from it even in this hot weather, no way of measuring the losses but the other half said it was no good as an airing cupboard as it was the same temp as the house !

[Mr Punter]

 

1 hour ago, AliG said:

As the heating has been off for some time we continue to use a substantial amount of gas for hot water and I calculated that the heat loss in the hot water circuit probably runs to £100s a year ( actually I calculated it at about £2.50 a day if it ran constantly, probably about £1 a day for the amount we are running it), more than most people use for hot water all together. It is probably not helped by the builder not insulating the circuit. He deemed it unnecessary as they are all within the house. this might have helped but I think the heat loss would still be quite substantial.

 

What a cowboy.  This needs to be insulated to comply with building regs in England.  I can't imagine this being different in Scotland. 

[SteamyTea]

1 hour ago, JSHarris said:

but a double thickness insulation one supplied by Newark.

That was a design that had a cold tank above the hot cylinder, and some pipes running up the side wasn't it.

 

My cylinder is a bog standard E7 one of 220 lt.  Cold in the bottom, hot out the top, top pipe bends 90° then a T. One side goes to the FE tank in loft and other side supplies hot water.

Initially I had losses similar you @JSHarris, but by lining the cupboard with 100mm celotex and lagging the pipework I now have that down to very little.  Less than 0.5 kWh/day and probably less.

So don't dismiss an ordinary system on a standard heat loss assumption, it can be easily overcome.

[Gone West]

5 hours ago, Nickfromwales said:

 

Firstly, the least amount of kit. 

Secondly, the least amount of service / maintenance.

Thats a simple system.

 

Well for my house that is a Genvex Combi 185LS. Compact and everything in one box. It works for us but wouldn't work in every house and I don't think there is a 'one size fits all'.

[newhome]

6 hours ago, Triassic said:

The bottom line for me is to understand what an optimum system looks like.

 

I’m not even going to start describing mine, suffice to say don’t go there!!