Heating options to satisfy SAP calcs

[Gavin]

Hi All,

 

I'm currently planning my first new build property. Money is extremely tight and I'm trying to keep my budget below £100k. I'm looking for suggestions on the best option on heating at the most cost effective option. Air pumps, LPG, oil, solar panels are all floating around but I'm not sure which is best.

 

Suggestions would be helpful!

 

Gavin

[Guest Alphonsox]

Welcome to Buildhub - Your best option is likely to be mains gas if it's available.

[MikeSharp01]

Yes everybody says mains gas but I have a worry that its not a sustainable source of energy, but then what is? Although you can pack one hell of a punch with a gas boiler most people on here build homes that are so well insulated & air tight that the energy requirement for heating is very low to non existent, Domestic Hot Water (DHW) is the main challenge. There is loads here on that challenge (just use DHW in the search box to find out just how much). Last week I was looking at our system and although I had sort of concluded that a combi boiler that could deliver 2 x 10l/min showers was the way to go after @Nickfromwalespointed me at a unit capable of doing it. I am wondering if that might be overkill but it does have the capacity for showers albeit at a cost £ and some small standing losses in the internal preheat system. Although the final system will be an exercise in optimising the compromises you can, in the end, decide much of the detail down the line provided, it seems to me, that you get the basic infrastructure right and make some decision up front. There are also some basic myths to dispel. They are (and I am not sure it helps to understand them):

1. Just because you don't have children and are happy to live the life of a hermit / hippy (nothing against them some of my best friends still are) the people who will purchase your home from you or your estate will pay more for stuff they understand (get).
2. The price of energy is low. True it is now but won't always be.
3. Being self sufficient in energy is a good thing. Not necessarily true because you have to live with your neighbours and they with you so unless you can find a self sufficient solution that relies on no technology you will have to rely on somebody just to keep making the service parts etc.

This leads to some upfront decisions - these appear to be:

 

Want to be a) net exporter of energy (SAP > 100), b) use no external energy, sum of external input - generated output = 0 (SAP = 100), c) use some external energy (SAP <100)

If you go for options a) then you will inevitably need some sort of energy storage system to smooth out the generation curves you are likely to get unless you have access to something like Hydro generation and even then...
 

We have : Natural Gas, E7 or E10 but will need to change supplier, Sun - so could have PV or ST

We don't have: Provision for wind (not enough space), Hydro - no flowing water to speak of,

We won't have: GSHP -small area available but costs very high, Oil & LPG

So far on my list of 'infrastructure' I have:

1. Ducts to get ASHP services into the the building and to the plant room (at this stage I don't intend to install an ASHP) but given the cost of small piece of ducting....
2. Ducts to get additional PV, for garden mounted PV cells, into the building and to the plant room.
3. Ducts, or just routes, to get Roof mounted PV services to the plant room.
4. Enough room, and wall pattressing (extra strength in the walls), in the plant room for the; MVHR, a Thermal Store (TS) or UnVented Cylinder (UVC) or a phase transfer storage system, a boiler, a couple of heat exchangers, 3 - 4 pumps and associated valves, pipework & wiring. Space somewhere for the control panel (in our case not in the plant room but in the downstairs WC where one wall is spare! - there are reasons.)
5. UFH - which we technically don't need, Passive House Planning Package (PHPP) says warm air will be enough, but it unlocks a whole mass of possibilities for heating, cooling and moving heat about. See the @JSHarris blogs for more on that. I will not terminate the UFH other than to pressurise it for testing and during the slab pour. I think the cost of installing it will be around £400 but I, or my descendants, will get this back from the people who buy it safe in the knowledge that it has UFH available - not many people understand hot air although a lot of people generate it.
6. Provision for in duct cooling and heating around (or in if you can afford one with it built in again see @JSHarris) the MVHR box. Can be fed from boiler, or ASHP if installed or could be electric heating (cooling not simple with electricity alone)
7. Masses of insulation around the plant room to help with any standing losses, effectively isolating it from the house so what happens in the plant room stays in the plant room. I would like to eliminate standing losses if I can, I am sure I read somewhere here that @SteamyTea got to a point where his DHW energy use was the same as the standing losses so 50% of energy is notionally going to waste but probably heats the house in winter but is a problem in the summer. Using the MVHR to extract warm air from the plant room and redistributing it make sense but the cost of generating it in the first place needs to be considered - IMO
8. I have also provisioned for a battery store adjacent to the garden room and can use the existing electric ducting to carry the connections back to the house and generation points.
9. Have kept waste water separate from the raw sewage down to the plant room in case I feel the need to deploy waste water heat recovery via a simple heat exchanger. (Added 21/11/2016 when reminded)

 

Some things imply other things so:

• if you go for ST then you probably will need at Thermal Store and a UVC won't work.
• If you have ASHP you will need supplementary systems to make DHW and you will probably need Underfloor heating and a buffer tank to optimise the ASHP output.
• It is unlikely that you will install both a TS and a UVC

 

In short its probably one of the most difficult choices out there if you have a conscience and want to do the best thing for your finances and the planet.

 

Hope this helps - could write a book by combining the people on here but I am not sure you would arrive at a consensus unless its to agree that there is no one right answer.

Edited November 21, 2016 by MikeSharp01

[joe90]

Mike, a very comprehensive piece above, i know I am in the same place trying to decide and future proof, however re Steamy Tea,s losses, he got his DHW standing losses down to quite near the phase change level by reducing DHW temp and lots of insulation. ( 1Kwh verses 0.6Kwh in think from memory but he will be along shortly to correct me ?)

[jack]

21 hours ago, MikeSharp01 said:

• If you have ASHP you will need supplementary systems to make DHW and you will probably need Underfloor heating and a buffer tank to optimise the ASHP output.

 

This isn't quite our experience.

 

We have an ASHP that runs to 55 degrees (5kW Panasonic Aquarea).  I haven't experienced (or at least noticed) a lot of defrosting going on, although I only have last year's very mild winter to refer to.  

 

We presently top up the upper quarter of our UVC with the immersion to 80 degrees early every morning once the ASHP has the entire tank up to 55 degrees.  Based on recent analysis, I'm not sure this is actually required - we always have quite a bit of hot water left at the end of the day.  I'm about to start some experiments to see whether I can reduce or even do away with the boost, which would save up to 3kWh per day.

 

We don't have a buffer tank.  With in-slab UFH, I doubt there's any need, as the slab is its own buffer.  I'm not sure whether this would be the case where a thinner screed is used.

[MikeSharp01]

Yes Jack you can get by with 55 deg in the UVC but how many showers can you have and you still have the standing losses? Not sure but I get the impression that showers are at the core of all the DHW challenges.

[SteamyTea]

I think there are a few confusing things gong on here:

 

There is the 'best' future proof energy source.

The most efficient method of using that source.

The detail of using that source.

 

Quite simply, we don't know what the future holds, so we can only rely on history.

From research I have done in the past, the average energy bill is about 5% of the average wage, almost regardless of which developed country you are in.  This consistent mean pricing is brought about by different technologies and build qualities.

So you really need to look at other places in the Americas and Northern Europe to see what they are doing.

 

I also have a bit of a plea, can we stop talking of 'taking a shower', 'having a bath' or 'turning the heating on'.  These are very subjective terms and don't help anyone design and plan a system.

As an example, I have my 'heating on', it is a 1 kW fan.  It has been on for about 30 minutes, and as I am going out, will be 'off' in bout 10 (if the thermostat don't kick in).

I had a bath this morning, took 80lt of water at 42°C.

Now any of us can work out what we are using, so can we before we start talking about 'the top third of the tank' or whatever.

 

Numbers are needed to make these decisions.  Thanks.

 

[PeterW]

1 hour ago, MikeSharp01 said:

Yes Jack you can get by with 55 deg in the UVC but how many showers can you have and you still have the standing losses? Not sure but I get the impression that showers are at the core of all the DHW challenges.

 

You will still need a weekly legionella cycle to 68c to ensure the UVC is kept clean - but agree 80c seems hot ! 

[jack]

1 hour ago, MikeSharp01 said:

Yes Jack you can get by with 55 deg in the UVC but how many showers can you have and you still have the standing losses? Not sure but I get the impression that showers are at the core of all the DHW challenges.

 

Yep, I know 55 is plenty hot enough, but as you say, it's a matter of stored usable energy.  I need to figure out whether I need the extra energy associated with the top-of-tank boost.  Also, having the tank sitting at 55C should reduce standing losses over having some of it at 80C.

 

Complicating matters:

- I still haven't insulated all of the pipework yet, as I'm waiting on the final okay from the people doing the RHI stuff for me before fitting it.  At the moment, standing losses are a lot higher than I expect them to be once the insulation is done.

- We have waste water heat recovery on the two showers that are generally used.  That should increase how much usable hot water can be delivered, but by how much I haven't a clue!

 

(edited to add) And yes, in my experience, showering is the massively dominant factor for DHW usage.  We use a dishwasher, so only occasionally use hot water at the kitchen sink.  The runs to bathrooms are long enough that we don't bother with waiting for hot water to wash hands after using the toilet.  Other than washing up things that can't go in the dishwasher, and shaving every couple of days, I'm struggling to think what other DHW we actually use! 

 

1 hour ago, SteamyTea said:

I also have a bit of a plea, can we stop talking of 'taking a shower', 'having a bath' or 'turning the heating on'.  These are very subjective terms and don't help anyone design and plan a system.

...

Now any of us can work out what we are using, so can we before we start talking about 'the top third of the tank' or whatever.

 

I get what you're saying, but I don't completely agree.  It is a fact that I presently boost the top portion of our 250L tank to a higher temperature than the 55C generated by the ASHP.  It is also a fact that we don't ever seem to run out of water despite my particular family's usage of 4-6 showers a day.  I speculate that I can reduce the amount of boost while still not running out of hot water, and when I get the chance I'll do so and report back.  

 

Unfortunately, our bathing activities can't be as simply characterised as "X litres of water at Y temp", because our day-to-day showering activities are hugely variable. 

 

13 minutes ago, PeterW said:

You will still need a weekly legionella cycle to 68c to ensure the UVC is kept clean - but agree 80c seems hot ! 

 

80 degrees is the stat temp on the immersion element.  There's a one hour boost controlled by our immersion diverter after the ASHP is finished its work.  I haven't yet got things set up to be any more clever than that!  

[PeterW]

1 hour ago, jack said:

[...]

I get what you're saying, but I don't completely agree.  It is a fact that I presently boost the top portion of our 250L tank to a higher temperature than the 55C generated by the ASHP.  [...]

 

80 degrees is the stat temp on the immersion element.  There's a one hour boost controlled by our immersion diverter after the ASHP is finished its work.  I haven't yet got things set up to be any more clever than that!  

 

Ok so I'm now interested as I've gone for 300 litres at 68c giving me enough hot water with ASHP on E7 from 3-5am at 48c and then the immersion doing the top up from 48-68c up to 6:30am. ASHP will then kick in to do the slab from 5-6:30am but at 30c. 

 

Two questions @jack

 

- do you have any TMVs prior to the showers or do you feed water at 80c to the shower ..?

- how much do the showers use per minute ..?

 

Now wondering if 300 litres is overkill ..!!

[jack]

46 minutes ago, PeterW said:

- do you have any TMVs prior to the showers or do you feed water at 80c to the shower ..?

 

All hot water is fed via a TMV on the UVC.  Can't remember what temp that's set at - it's whatever the standard is for that kind of valve.

 

46 minutes ago, PeterW said:

- how much do the showers use per minute ..?

 

That's an interesting question actually!

 

We have good static and dynamic water pressure here - something like 6 bar static.  Our plumber was concerned about making sure we had good water pressure throughout the house, while still comfortably satisfying the water usage requirements for a new build.  In the end, he installed a 1.5 bar pressure restrictor on the way into the house.  This means that our showers are fairly low pressure.  I thought this would really annoy me, but it isn't that bad, and it does force us to use less water (I'm the only one in the house who would ever turn a shower on less than full bore!) 

 

The main problem is the pressure drop when the shower is on and someone else turns on a tap or the water softener goes into a regeneration cycle.  There's still a tolerable amount of shower flow when that happens, but the pressure drop is quite noticeable.

 

The plumber will come back and put in a higher pressure valve once the house is signed off.

 

Let me measure the shower water usage tonight and get back to you.

 

Edited to add: are you going for a single immersion?  I've got one just above the ASHP coil, and another about a quarter of the way from the top, and I can choose which one to boost.  When it's sunny, the diverter does the top portion first, then switches to the bottom immersion.  Many days in summer we ended up with a full tank at 80C by lunchtime - for several months the ASHP simply didn't ever turn on!

[joe90]

With regarding future proofing I meant it as cables and pipes to multiple locations to cope with a change of mind in the future, a bit like installing UFH pipes in the ground slab just in case you decide to use it in the future.

[ProDave]

Question for Jack.

 

You seem to imply you only want to heat the tank once per day with the ASHP and hence the "boost" with the immersion to make it "last the day".  Is this so you can run it overnight on E7?  Otherwise I can see no reason why the ASHOP doesn't top it up as you use DHW during the day.
 

[jack]

Good question.  

 

We don't have E7.  My current setup is largely a function of inertia and a long to-do list!  When we moved in, there was so much to do that I didn't have time to optimise things.  I therefore just set it up to give us a full tank of 55C water in the morning (which is when we typically use more water), with an hour's top-up of the top portion to absolutely make sure we didn't run out.  I had grand plans to revisit this and at least reduce if not do away with the boost entirely.  

 

Further complicating things, I originally wanted to control all of this via my home automation system, but of course things don't really want to talk to each other.  The Panasonic apparently has an RS485 module that I could use to talk to the HA system, but it costs over £500 from memory.  I can't see the value in spending £500 to get slightly easier control over hot water!  

 

So the whole thing's been put on the backburner, and it's only now I'm starting to find the time to look at things like this.

 

You're right, there's nothing stopping me from doing a top-up during the day with the ASHP rather than the immersion, and that's what I'll likely look to if one tank at 55C is enough for the morning but not the whole day.

[joe90]

I, on the other hand plan to have E7 and run the ASHP overnight to get the slab warmed up and a tank of hot water for the day, either to be topped up manually during the day or by use of a modulating inline electric waiter heater. But the house is yet to be built ?

[PeterW]

I did think about the inline heater thing but an immersion run for 1hr at peak costs 36p.... Yes, that is £136 of electricity but even if I lose half of that as losses, I would still be using a third of that to do the top up using an inline heater. 

 

Add the capital cost and the inline has a payback of 4-5 years but it's another thing to go wrong ... adding another immersion to the tank (so only topping up the top 3rd) is around £80 and my running costs drop to £40 a year - now we are at 6 - 7 years payback and if I go for a few solar panels then it's starting to become the law of diminishing returns. 

 

One well insulated airing cupboard / hot press / plant room later and I'm now starting to question the inline and all of its hassle just to save what is small change in the cost of the build.  

[ProDave]

And I plan to be different again and have solar PV (almost certainly without any FIT by the time I get there) so the emphasis will be on maximum self usage.  So the daytime is when the HP needs to be working most, not over night.

 

if I had my way, a dribble of luke warm water from yesterday would be plenty for a morning splash of the face, and let the HP do it's thing when the sun is up for a nice tank of water for the evening which is when we do the washing up (don't let anyone tell you a dishwasher does away with washing up, it just reduces it and deals with the fiddly stuff) and for my evening shower.  For this "plan" to work, I have to convert SWMBO to having an evening shower rather than a morning shower. Any advice in that department appreciated.
 

[PeterW]

If it's a UVC, can you not just run the immersion for an hour at E7 rate (i.e. 12p worth...) to heat the top of the tank ..? Then SWMBO can have her shower in a morning and marital harmony shall be restored ....?

 

You could then offset that during the day and it would probably be nett zero by the time you had finished. 

 

Also so makes sense running the legionella cycle during E7 but not sure you would manage to get her down to one shower a week...

[SteamyTea]

As an experiment 2 years ago, I heated my 200 lt, E7, unvented cylinder to 50°C, then turned it off.  Having my usual short showers of about 30 lt of water at 38°C, it lasted two days.

So that was about good enough for one person and about 100 lt of water that was warm enough (the last shower it was as hot as it could go, no cold added).

As some of you may know, I have limited the times that my E7 comes on to around a maximum of 3 hours a night, so 9 kWh in total.

I should really try and find the data and repeat the experiment as I now have more insulation around the cylinder.

 

6 minutes ago, PeterW said:

If it's a UVC, can you not just run the immersion for an hour at E7 rate (i.e. 12p worth...) to heat the top of the tank

This is something I have thought of doing, just a bit of rewiring and heating less of my cylinder.  Generally, if the water has dropped to below 35°C, then half an hour of topping up (1.5 kWh) is enough for a bath.

[ProDave]

27 minutes ago, PeterW said:

If it's a UVC, can you not just run the immersion for an hour at E7 rate (i.e. 12p worth...) to heat the top of the tank ..? Then SWMBO can have her shower in a morning and marital harmony shall be restored ....?

 

You could then offset that during the day and it would probably be nett zero by the time you had finished.

 

Also so makes sense running the legionella cycle during E7 but not sure you would manage to get her down to one shower a week...

That assumes I am prepared to pay the higher standing charge and higher daytime rate, jut to get a few KWH cheaper at night.

 

But I like the thinking of immersion heat just the top half of the tank for "her" morning shower and the legionella cycle. As long as half a tank lasts 25 minutes or I will be in trouble.........
 

[SteamyTea]

1 minute ago, ProDave said:

As long as half a tank lasts 25 minutes or I will be in trouble.........

Then you will be needing a 500 lt cylinder then

[Stones]

1 hour ago, PeterW said:

I did think about the inline heater thing but an immersion run for 1hr at peak costs 36p.... Yes, that is £136 of electricity but even if I lose half of that as losses, I would still be using a third of that to do the top up using an inline heater. 

 

Add the capital cost and the inline has a payback of 4-5 years but it's another thing to go wrong ... adding another immersion to the tank (so only topping up the top 3rd) is around £80 and my running costs drop to £40 a year - now we are at 6 - 7 years payback and if I go for a few solar panels then it's starting to become the law of diminishing returns. 

 

One well insulated airing cupboard / hot press / plant room later and I'm now starting to question the inline and all of its hassle just to save what is small change in the cost of the build.  

 

I likewise thought about an inline heater, but came to the same conclusion. I couldn't see the point in introducing an additional layer of plant when I can deliver what I want from a single ASHP / Cylinder package.

 

We all want to save money and minimise our energy consumption, but I think there are some things where comfort and convenience are more important, and having plenty of hot water on tap, is one of those things. If it costs a little more / I use more energy / I use more water then so be it.

[PeterW]

I think I worked out that the difference was better spent on going from 250 to 300 litres and adding a second immersion and some logic around controlling the top third boost than adding the complexity of the online heater. 

 

If money were no object then I would go with Sunamps but with no PV to start with it's an expensive option. 

[joe90]

My reason for considering an inline heater was to optimise the DHW demand for the two of us for most days but when guests arrive no chance of running out of hot water or secondly should there be a failure in the normal syatem the inline heater would cover use till it was fixed.