Early stage thinking - new build

[DevonKim]

Hello helpful people 

 

I am at the very early stages of thinking about heating / hot water and solar generation in a new build, and I was hoping for some simple answers. 

 

I have a plot, and I am hoping to build a heavily insulated house on it, with a foot print of less than 100m², but an overall floor area of around 200m² (a main block which will be 3 stories using attic trusses for the third storey, and a single storey "wing").  I would like underfloor heating no matter what, and I intend to install solar panels on a south facing roof area, hopefully connected to some kind of storage.  I'm in Devon, and we rarely get snow, or prolonged negative temperatures, however, we occasionally get > 25^oC

 

I would like the temperature in the main rooms to be around 19^oC, and about 16^oC in the attic bedroom.  Most of the time there will be just me in the house, but there will be occasional visitors, including my partner or my father, both of whom are overall less cold tolerant than me. 

 

Q1.  Would an air source heat pump be able to achieve those sort of temperatures?  I have been somewhat put off ASHP by reports of people having to wear thick jumpers in the house, but I suspect that is for retrofit ASHP?  Has anyone got one up and running that could give me an idea of how well it works for them?  

 

Q2.  If I wanted to avoid gas altogether, is that likely to be a good idea? There is a gas connection available, but I am thinking more about the standing charges than anything else.  I'm happy to cook on electric, but was wondering about water heating.  I like baths at a high temperature! 

 

Q3.  I rather like the little "Everhot" stoves, partly because they seem to avoid the problems with either overheating or airtightness that a woodburner seems to have, would that clash with the ASHP setup in any way, or would individual room temperature control mitigate any issues? 

 

Q4.  What else do I need to think about at this stage?  Designing in a plant room?  Ducting? 

 

Q5.  Has anyone got one of the Octopus heat pumps yet?  Is it any good?  And has anyone got an Octopus electric only tariff?    

 

Apologies for asking what may seem like basic questions, I am slowly but surely getting up to speed with some of the technical issues, but could do with a simplified overview first 🙂 

 

Kim

 

 

[SteamyTea]

Kim 

There are no easy answers to your question. But there is basic school physics.

 

ASHPs and jumpers would be normal in any house. Why would you want, in a UK winter, to be dressed in Cornish National Dress (even in Devon). If people want a very hot house, then fit a larger heating system.

 

The way you design, and orientate your house can have a large effect in the energy usage, it is all about surface area to volume ratio. 

PV on a roof will absorb about 20% of the energy hitting it, helps to keep the rise in temperature down. 

Cooling can be combined with MVHR. MVHR is usually designed for minimum requirements, but there is nothing to stop you oversizing so that a usable amount of heating and cooling can be delivered/dispersed.

 

An ASHP can cheaply and reliably deliver DHW to 50⁰C. Plenty hot enough for a bath. Just a case of sizing the storage cylinder correctly.

 

Really just a case of sitting down and working with the numbers. Dull and boring, but pays dividends.

[Iceverge]

Welcome welcome.

 

Reading this and looking at your requirements my mind instantly turned to cooling not heating. If you require 16deg in the attic you'll need air conditioning! . 

 

Your design sound eminently sensible. Minimal outside wall makes a house better to heat and cheaper to build. 

 

Given your location passivhaus will be easily achievable with a good builder or a package build like MBC timberframe. 

 

Q1. Easily in a new house with good insulation. Plan on 300mm EPS in the floor. 300mm EPS/cellulose/mineral wool in the walls 3-400mm cellulose in the roof. 

 

Q2. Yes avoid gas. It is bad for internal air pollution and health.  We cook on induction. Cooking is better than gas having lived with both. Cleaning the hob is simple. The only annoying bit is the touch controls are a pain at times. ASHP can generate plenty hot water. Size you tank as large as possible though 300l minimum. Bigger is better. This will allow you to store your water at 50deg meaning better ASHP efficiency. 

 

Q3. I don't know much about them but they're AGA style electric cookers AFAIK. 

 

The smallest one in the range does 1.5kW which on its own is lightly to exceed your house heating load for most of the year. Assuming it will take an age to heat up like cast iron cookers of yore you'll lightly not be able to get inside the kitchen with the heat by the time it's ready for use. I could be wrong and it might be ok in a large open plan room, but caution is required. 

 

Q4. If you share some sketches there's plenty of knowledge here, most of us have learned through getting it wrong! 

 

Q5. Pass. 

 

 

Other thoughts. 

 

Build a compact, airtight shape with due regard for overheating. ( Appropriate glazing, shading , blinds, ventilation, high decrement delay roof and wall buildups)

 

Use an ASHP for UFH on the ground floor. Get one that can cool the slab too. 

Put a multi split A2A unit ( air-conditioning) upstairs on the 2nd and 3rd floor for cooling and maybe winter heating (you really won't need it)

 

Best of look and looking forward to following your progress. 

 

Edited May 7, 2022 by Iceverge

[tonyshouse]

I would start with target u-values, for me less than 0.1 for walls, floor and ceilings 0.7 for windows 

 

you may then find that you can design out heating, heating bills, servicing costs, repair costs replacement costs 

 

1, Gshp better cop, 2 good idea, 3, 4 &5 pass 

[tonyshouse]

Design out thermal bridges, design in insulation, ducts MVHR, solar, shading 

[joe90]

Well I have just finished my build in North Devon, not passive but not far off, a 5kW ASHP with UFH , heating required only a couple of months a year, plenty of hot water all year. (And I very rarely wear a jumper indoors). Orientation is key IMO I have a south facing conservatory and that heats the house in the shoulder months. Having MVHR means no trickle vents (draughts) and heat recovery. I was told my house would overheat with South facing and a conservatory but as yet I have not needed cooling (which the ASHP can do with a bit of work).

[Bramco]

1 hour ago, DevonKim said:

Q5.  Has anyone got one of the Octopus heat pumps yet?  Is it any good?  And has anyone got an Octopus electric only tariff?    

 

I looked at the Octopus heat pumps but had the feeling they were intended for retrofit, i.e. high temperature HPs.  If you are going for UFH throughout, you only need a low temperature heat pump.  These can heat your hot water OK but can't deliver the temperatures needed for radiators.  Take a look at the Cool Energy ASHPs -> https://bit.ly/3sfBf6L.  

 

We have just had our electric supply connected and have Octopus electric only tariff.  Once you are connected and on their tariff you can switch to Octopus GO which gives you 4 hours of 7.5p/kW at night which can run the ASHP, or can be dumped into your hot water tank.

 

Simon

 

PS There's plenty of info on the forum about all of the other questions you've asked as well as some blogs from members that have been through the design process explaining how they made their decisions.  

 

 

[Jilly]

It seems heating is a bit of a black art. That's really hard to accept when you've decided to plan and get things right and part with all your hard earned cash...

 

It seems to me you can only be about 80% sure how a building will perform in real life. Keep reading until you reach a point you can accept you have protected the downsides for your situation as much as possible.

[ProDave]

9 minutes ago, Jilly said:

It seems heating is a bit of a black art. That's really hard to accept when you've decided to plan and get things right and part with all your hard earned cash...

 

It seems to me you can only be about 80% sure how a building will perform in real life. Keep reading until you reach a point you can accept you have protected the downsides for your situation as much as possible.

If you know the calculated U values of all the walls roof, floor and windows you can calculate the heat loss pretty well.  I used Jeremy's heat loss spreadsheed and the result was very accurate.  I confirmed the building performance almost as soon as it was complete, long before the UFH was down and the internal fit done, just by running a single low power electric convector heater for a few days and plotting internal vs external temperature and calculating the heat loss from that and it agreed with the heat loss spread sheet.  So I then knew I could trust those figures to design the UFH system.

[joe90]

1 hour ago, Jilly said:

It seems heating is a bit of a black art.

Well I did no calcs whatsoever and many here will chide me for admitting it. I built with a fair bit of insulation, double glazing and attention to detail regarding air tightness, bought a 5Kw ASHP as a punt and it all works fine. I do have a woodstove as backup (and the looks on a cold winters day) and plug In heaters for bedrooms if the temp is dire (not needed yet). I don’t see why you have to size a heating system for the two coldest weeks of the year . Despite @ProDave using Jeremy’s heat calcs and it working ok, is was not fir Jeremy, he ended up needing more cooling than heating after it was finished, but we think that is down to the location (sun trap in deep valley) which don’t tend to figure in the calculations used.

[DevonKim]

Thank you very much everyone, that's really helpful.  

 

It is great to know that my early thinking processes are not too far off, and I'll have a rummage around the site to find other people's calcs and design thinking.  I'll also upload a couple of my early sketches, as I can see that people on here have been really helpful with other people's designs.  Part of me thinks that I'm being unimaginative with my designs, as it is a fairly square box, but I wanted something simple to construct and not too many fiddle details to sort, so it is nice to hear that the box shape is also going to pay dividends on the heating front.  

 

I'm agree with @SteamyTea about the jumpers, happy to dress properly for the weather, but my old house was properly cold & damp, and it started to have an impact on my joints.  From everything that I am reading on here that is highly unlikely to be an issue with a newbuild timber frame with the right U values and orientated properly.  

 

This is the little Everhot, and I was thinking of putting it in the living room, as a bit of a focal point.  I don't have a TV, so it might be nice to have something pretty to look at, and woodburners don't seem to go with the ultra-insulated ethos.   You can turn it down to trickle heat, but I suspect that it might overheat the room given what people are saying.  

 

 

However, it is electric, so no need for flues, vents or anything like that, and you can stick your feet in it on a cold day 😁

 

 

 

Edited May 7, 2022 by DevonKim
added detail

[joe90]

2 hours ago, DevonKim said:

Part of me thinks that I'm being unimaginative with my designs, as it is a fairly square box,

Similar to mine, oblong box with longest wall facing south, small windows to the North 👍

[SteamyTea]

Unlike @joe90's home.

Consider filling the roof with integrated PV.

WIth careful choice of module sizes, and no hips, you can get a lot if kWs on. Then connect up as needed.

It is expensive to do it afterwards.

If you are having a room in the roof, consider not having any windows on the PV side. That way you have no shading, less overheating and enough natural light half the year. North facing windows give a nice light.

[ReedRichards]

Q1)  There is nothing magical about ASHPs; they are as capable of heating your house as a gas, oil or electric boiler.  However retrofitting an ASHP without changing the radiators is a recipe for a cold house with a high running cost.

Q2)  Typically you would heat your water to 50 C or less with an ASHP.   At 48 C you would suffer second degree burns after 15 minutes; given that the water in the bath would cool you might just get away with a 48 C fill.

Q3)  That electric stove will be heating your room at least 3x the cost of using the heat pump.  But if you put a TRV on the radiator in that room and locate any control room thermostat somewhere else then it should not interfere.  

[Iceverge]

I can't see that small unit being a problem. I was thinking you might be planning on putting one of these in your kitchen. 

 

 

Worse case it only gets used infrequently but I do enjoy occasionally shutting our sitting room door and getting it up to 25 deg+ with our convection rad. 

 

On 07/05/2022 at 13:58, DevonKim said:

  Part of me thinks that I'm being unimaginative with my designs, as it is a fairly square box, but I wanted something simple to construct and not too many fiddle details to sort, so it is nice to hear that the box shape is also going to pay dividends on the heating front

 

Another square box here with much the same thinking. No regrets with the shape of the shell but maybe we should have altered the layout a little inside. 

Edited May 12, 2022 by Iceverge

[ToughButterCup]

On 07/05/2022 at 12:21, Jilly said:

It seems heating is a bit of a black art. ......

 

Deliberately, I feel.  It just can't be kept simple because it's not in the sector's interest to be so.

 

You really can disappear down soooo many rabbit holes, and for your troubles, be pulled this way that way (... over the Irish sea ...) by one charlatan after the other.  Read @TerryE's posts and blog. At first, go for a percentage of understanding, and work up from there. I think I've re-read his stuff more than anyone else's. He sticks to facts, and keeps it simple....ish.

 

You can read this board about heating until your eyes bleed, cross themselves and die. And still not know what the 'king hell to do

Bitter? Me? 

 

Know why you are choosing the heating design that you want : and - more importantly - why you are not choosing  any other from all the  designs available.

 

 

Edited May 12, 2022 by ToughButterCup

[SteamyTea]

56 minutes ago, ToughButterCup said:

just can't be kept simple because it's not in the sector's interest to be so.

Just think of heating as a radiative model.

Add energy to any material and electrons will be raised up an orbital level. Then, as the electrons drop down to the more stable position that they prefer to be in, a photon of light is produced. This photon can be thought of as pure energy. 

That photon will soon hit another electron, raising the energy, only for that energy to be released again. This goes on forever (or untill all electrons are at the lowest energy state).

Sometimes there is not enough energy to move an electron up a level, but enough to twist, turn and unbalance the whole atom. This is how energy is stored. Some materials soon rearrange themselves, giving up that heat quickly, others take there time, so can store energy for longer. 

So like a game of snooker, bounce balls of each other, but just think that instead of the colours being worth more points, they are just different materials with different energy levels waiting to be released.

 

What's hard about that.

 

 

[ToughButterCup]

Thanks for making the effort. 

Where to you delight in radiative models, I delight in learning to be a better carpenter.

 

I can see sawdust and shavings . But heat, temperature, warmth, joules, kWh, Ergs, pv .... I'm with @Jilly

Edited May 12, 2022 by ToughButterCup

[SteamyTea]

28 minutes ago, ToughButterCup said:

I delight in learning to be a better carpenter.

 

I can see sawdust and shavings

It is the same, really.

With the sawdust and shavings being the inefficiency of the process.

If you start with the plant growing, energy forces the chemical rearrangements.

Then, when you saw and chisel, you are adding energy to break those chemical bonds, usually causing a rise in temperature (I bet you have touched a drill bit right after use).

So rather than think of woodworking in a top down manner i.e. what saw blade is best, think if it from bottom up i.e. how strong are these bonds, do I need lots of small cuts, or fewer large cuts.

 

Richard Feynman was once accused of not appreciating the beauty of nature, his reply was along the lines of:

"I can see the beauty in a flower, just like everyone else. I can also see the beauty of how the cells are arranged, and the atoms that make those cells, and the equations that describe those atoms".

 

Got to be better than just using a bigger hammer.

Edited May 12, 2022 by SteamyTea

[DevonKim]

2 hours ago, Iceverge said:

 

Another square box here with much the same thinking. No regrets with the shape of the shell but maybe we should have altered the layout a little inside. 

 

 

Gosh that big stove / range is pretty, isn't it?  

 

What would you alter about your internal layout, and why?  

[DevonKim]

3 hours ago, ToughButterCup said:

 

 

Know why you are choosing the heating design that you want : and - more importantly - why you are not choosing  any other from all the  designs available.

 

 

 

I'm choosing underfloor heating as a distribution method because I have too many books, and radiators get in the way of bookshelves 🙂 .  

 

More seriously, it does sound as though an ASHP in a new build with underfloor pipes is an effective and cosy way of heating for me.   And it may be different for other people.

 

I think it is very easy to spend ages agonising over the choice, when each will have advantages and disadvantages, just different advantages and disadvantages, so there is no "right" choice.  It can be easy to become paralysed by indecision, when sometimes just making a decision, and accepting that there will be some disadvantages associated with that decision can get a project moving.   

  

Edited May 12, 2022 by DevonKim

[Iceverge]

3 hours ago, ToughButterCup said:

be pulled this way that way (... over the Irish sea ...) by one charlatan after the other

 

 I think I just heard an arrow fly past my ear !!?

 

 

13 minutes ago, DevonKim said:

Gosh that big stove / range is pretty, isn't it?  

 

 

Yup, I was dead set on a range cooker too but logic (and cost) beat me down. 

 

14 minutes ago, DevonKim said:

What would you alter about your internal layout, and why?  

 

We ended up with big rooms and not much built in storage. We had a hot press with the water cylinder upstairs ( a hangover from an earlier design with a boiler stove) and there was no need for it. A walk in wardrobe would have been better use of the same space. 

[SteamyTea]

7 minutes ago, DevonKim said:

I think it is very easy to spend ages agonising over the choice, when each will have advantages and disadvantages, just different advantages and disadvantages, so there is no "right" choice

When the USA decided to put a man on the moon, they did not know, in detail, how they would achieve it.

So they made the big decisions first i.e. man on moon and return.

Then looked at the next big decision, getting to orbit, why they used a 3 stage rocket, was all that was realistic at the time.

Then the journey between Earth and Moon.  Easy, a large enough container to live in.  And so forth.

What they did not do was get stuck on details like the size of windows and the colour of the bog, all that flushes out later.

 

So make those big decisions now, write them down, amend if necessary, get an orderly list, then start to go into detail.  Much of the detail can be changed easily.

 

So

 

How large is the house--> 1 or 2 storeys-->Number of rooms

 

Running Costs--> very low or ordinary--> renewables energy or traditional

 

Build Type--> quick to watertight or quick to completely finish

 

And so on.