Advice Required for New Build

[umiq88]

Looking for some advice regarding design of a new build bungalow. Plenty of experience repairing or adding on small parts to systems but no experience designing a system and want to get the basics right.

 

Please don't tell me to hire a plumber. I have the greatest respect for trade/craft people and what it takes to do good work. I'm competent and have equipment and knowledge to install just not design.

 

200sqm new build bungalow will be putting in oil fired central heating with unvented hot water cylinder.  All heating in underfloor and there is 2 bathrooms (2 showers and 1 bath). The layouts lends itself to 3 manifolds but I can put 2 in if recommended

 

There will be 150mm (2x 75mm) Kingspan TF70 in the floor I was planning on running the cold water pipes through the middle of the insulation and the hot water pipes in the screed.

 

Questions are 

- How to size boiler and nozzle?

- How do I ensure boiler operates as efficiently as possible in condensing mode. 

- Expected oil consumption for a year (based on average consumption not calculated) Would I get away with 500l tank.

- How to size water tank? Will likely be installing thermal solar if funds allow.

- How to size pipework?

- Read a lot about cycling issues etc plan is to install a buffer tank in 'hot press' to act as airing cupboard and prevent short cycling. How to size this or is there a better solution?

 

Really I want the system to be as simple, efficient and reliable as possible. Least about of equipment etc. however if it would make a difference such as speed control for circulating pump then I would be happy to put in.

 

I understand this leaning into professional advice and if someone has recommendation I would happily pay for the advice.

 

Also any good books/publications for plumbing and central heating in new builds.

 

Edited September 4, 2023 by umiq88

[Big Jimbo]

You sound like me. I'm more than able to run pipes, connect up etc. However when fitting anything other than a basic system i think there is a lot you can get wrong. I'm going to try and at least get somebody to design a system for me. Whether i end up fitting any of it myself, we shall wait and see.

[JohnMo]

Can you upgrade to 200mm insulation?

 

Put cold water pipes below all insulation, pipes need to in conduit. Run pipes from a cold water manifold.

 

200m2 why would you need 3 manifolds. One should be fine, doesn't really matter the layout.

 

Add electric towel rads to the design also.

 

Why oil on a new build, I did gas and now have ASHP, it comes with the benefit of cooling also. Oil isn't the smart way to go, your heat loads are such that you will struggle to control the boiler without going thermal store.

 

Ashp, operate as a single zone, no buffer, UVC and 3 way valve, job done.

 

[Dave Jones]

be very difficult to pass SAP with oil burner on a new build.

 

Do it properly and ASHP.

[Conor]

100% possible for a careful and competent DIYer. Did most of my design and install myself. That, along with the MVHR work was the biggest saving over hiring a trade.

 

With 200m² UFH area, you're looking at fair amount of pipe work and water volume. If you run it at as a single zone, then you may not need a buffer.

 

For what you need re pipe spacing, boiler size etc, you'll need to do a detailed heat loss calculation, then an UFH design in likes of loopcad.

 

You'll also need to design it as a low temperature system, i.e. low flow temps suitable for an ASHP to pass new building regs. This is where correct setup of blending valves water volume etc is a challenge. Boiler will be wanting to send out water at 55c and see it back at 45c. But your UFH will want something like 30c. 

 

Best of luck, keep asking questions. I do agree with others re ASHP, but it's not my build.

 

One last thing, I don't think solar thermal stacks up compared to PV. With PV you can heat via a diverter bit also offset your own usage. Moot point if you don't have enough suitable roof surface tho.

Edited September 4, 2023 by Conor

[umiq88]

Upfront cost

Oil ~ €500 for good quality 2nd hand eq. I have tools and analyser to setup and maintain.

AHSP - >€5k I'm sure I can also maintain but don't have the equipment.

 

Running cost

Oil ~ 11c per kWhr

ASHP ~ electricity here (Ireland) is 44c per kWhr if you assume an average of 200% efficiency then that's 22c. Does anyone have any real life yearly averages for efficiency?

 

My logic is running cost of oil is cheaper and upfront cost is minor. If fuel prices change I can always switch to ASHP. And for any tree huggers out there oil is > 90% efficient, when the wind stops blowing and they burn gas to make your electricity I'd be impressed if you could get more than 60% after everything is factored in. I don't need advice about regs however everything will either be fully compliant or easily converted to be fully compliant.

 

Solar vs PV panels is down to your use and economics. Most people are borrowing money to install more efficient PV panels to charge more efficient electric cars (also bought on expensive finance). Thermal solar is cheap there are a lot of good 2nd hand stuff out there. My in laws have it installed >10 years and they almost never need to heat water for 4-5months of the year.

Edited September 4, 2023 by umiq88

[umiq88]

1 hour ago, JohnMo said:

Can you upgrade to 200mm insulation?

 

Put cold water pipes below all insulation, pipes need to in conduit. Run pipes from a cold water manifold.

 

200m2 why would you need 3 manifolds. One should be fine, doesn't really matter the layout.

 

Add electric towel rads to the design also.

 

Why oil on a new build, I did gas and now have ASHP, it comes with the benefit of cooling also. Oil isn't the smart way to go, your heat loads are such that you will struggle to control the boiler without going thermal store.

 

Ashp, operate as a single zone, no buffer, UVC and 3 way valve, job done.

 

 

Why 200mm? not disagreeing just wondering if there is a benefit? Insulation is PIR 0.022W/mK.

 

Layout is L shaped bungalow if I install one manifold I will have long runs to get to zoned rooms. I might try stick to 2 manifolds. Is it possible to use 1 pump and mixing valve for multiple manifolds?

 

I was planning on putting in 2 wet towel rails.

 

My plan for hot and cold water was to run 26mm Pex to each bathroom and kitchen. with a small manifold for each for sink/shower/bath. 16mm to sink and shower and 20mm to bath. 

 

How do you put cold water pipes below insulation? below that is concrete sub floor? If I sandwich between 2 75mm boards then I don't need to insulation and minor loss of insulation?

 

I presume it's ok to run DHW pipes (Pex) through the screed neext to U/F pipes.

[crooksey]

I run an ASHP and pay around £200 a month for my entire electric bill (summer is much cheaper), mines been refitted to an older property with insulation that wouldn't be the same as a new build. Been in over a year and im well impressed.

 

Replaced an old LPG system. They work so well with UFH and for a new build, I just (personally) do not see any benefit in choosing oil fired heating.

 

Go with 125mm pipe centres (nice low flow temp) . Get a decent screed over it, avoid solar thermal water heating, if funds allow go for solar PV to help run the ASHP.

 

Personally I don't like burying water pipes in screed, go through the walls or ceilings where possible for future remedial works.

 

I was very sceptical but had an old LPG system that was toast, was installing new UFH and screed (was very skeptical and again doing the work myself) but have been very impressed. 

 

If you really want oil I would just future proof your install with low pipe centres (125/100) and then put a decent manifold in so you can control the flow temp (not sure if oil boilers allow the same level of flow temp as a ASHP).

[crooksey]

Also TF170 at 150mm will be fine, may be cheaper to install eco therm (or others) at 200mm though.

[JohnMo]

47 minutes ago, umiq88 said:

AHSP - >€5k I'm sure I can also maintain but don't have the equipment.

 

Running cost

Oil ~ 11c per kWhr

ASHP ~ electricity here (Ireland) is 44c per kWhr if you assume an average of 200% efficiency then that's 22c. Does anyone have any real life yearly averages for efficiency?

 

My logic is running cost of oil is cheaper and upfront cost is minor. If fuel prices change I can always switch to ASHP. And for any tree huggers out there oil is > 90% efficient, when the wind stops blowing and they burn gas to make your electricity I'd be impressed if you could get more than 60% after everything is factored in. I don't need advice about regs however everything will either be fully compliant or easily converted to be fully compliant.

 

Solar vs PV panels is down to your use and economics. Most people are borrowing money to install more efficient PV panels to charge more efficient electric cars (also bought on expensive finance). Thermal solar is cheap there are a lot of good 2nd hand stuff out there. My in laws have it installed >10 years and they almost never need to heat water for 4-5months of the year.

I paid £1300 delivered for the ASHP.

200% efficiency in a new build is rubbish, should be circa 400%, flow temps should be never exceed 35 deg (at -9) except when making hot water

ASHP maintenance, give it clean, get rid of the leaves and debris, clean the filter the in the water lines. Done

 

In a well insulated house loop centres make little or no difference to flow temps required - maybe 1 to 2 degrees. I am running 300mm centres, only require 35 degrees at -9 to keep house warm. All fully calculated in LoopCad.

 

Oil boiler, thermal store, gives a long burn, no buffer needed, less messing about getting jetting right r making sure the sizing is exact, can just run flat out if you want.

 

 

[JohnMo]

2 hours ago, umiq88 said:

Why 200mm? not disagreeing just wondering if there is a benefit? Insulation is PIR 0.022W/mK.

Basically what's under the insulation is the ground at approx 6 deg or if block and beam outside air temp.  The room above the ufh will be circa 20 deg. At the same time the UFH pipes will be circa 30 to 35 degs. Heat tries to move from hottest to coldest, so temperature flow is always trying to move towards the ground, reluctantly moving upwards. The more insulation you have the lower the flow temp you need. The lower the downward heat loss, which can be big with UFH compared to radiators.

 

150mm compared to 200mm is circa 50% additional downwards heat loss.

 

3 hours ago, umiq88 said:

My plan for hot and cold water was to run 26mm Pex to each bathroom and kitchen. with a small manifold for each for sink/shower/bath. 16mm to sink and shower and 20mm to bath. 

The run off time to get hot water could be long. I am using 16mm and that wait can be long enough.

 

3 hours ago, umiq88 said:

How do you put cold water pipes below insulation? below that is concrete sub floor? If I sandwich between 2 75mm boards then I don't need to insulation and minor loss of insulation?

My floor build is 150mm reinforced concrete, 200mm insulation, 100mm fibre reinforced concrete.

 

I ran my pipes in flex conduit tied to rebar and cast in place.

 

3 hours ago, umiq88 said:

presume it's ok to run DHW pipes (Pex) through the screed neext to U/F pipes.

You need to run conduit so in theory they are removable. I took my DHW pipes up and ran above ceiling level

 

[Temp]

We started building in 2005. Went for oil fired UFH. Decided to install a 300 L thermal store to give good flow rate for showers and try and reduce boiler cycling (Oil boilers don't modulate the flame down to suit demand, they cycle the flame on and off instead). This took some fettling to get it to work right, possibly because my boiler is a bit too big. These days I would fit a lot more insulation and aim for ASHP. 

 

If you really want oil I would probably fit two tanks instead of a thermal store. One tank used for DHW and one as a buffer for the UFH. That would be the easiest to switch to ASHP later.

 

Our thermal store has too many pumps and mixers on it that leak a lot of heat into the room it's in. Fortunately that's not a problem other than one of cost - but I'm glad it's not in the master bedroom cupboard.

[umiq88]

17 hours ago, JohnMo said:

I paid £1300 delivered for the ASHP.

200% efficiency in a new build is rubbish, should be circa 400%, flow temps should be never exceed 35 deg (at -9) except when making hot water

ASHP maintenance, give it clean, get rid of the leaves and debris, clean the filter the in the water lines. Done

 

In a well insulated house loop centres make little or no difference to flow temps required - maybe 1 to 2 degrees. I am running 300mm centres, only require 35 degrees at -9 to keep house warm. All fully calculated in LoopCad.

 

Oil boiler, thermal store, gives a long burn, no buffer needed, less messing about getting jetting right r making sure the sizing is exact, can just run flat out if you want.

 

 

Hi JohnMo 

 

Do you mind sharing your model and supplier? 

 

I'm toying with the idea of fitting ASHP instead of thermal solar if its cheaper and switching between the two based on current price.

 

I'm talking average efficiency over the year. Your heat pump is not going to achieve 400% in the height of winter when you need it the most. On the other hand when its most efficient in summer you don't need the heating and for hot water it can't reach the 60degrees required.

 

I'm not here to knock heat pumps I just don't see how they're cheaper to run than oil and thermal panels.

 

 

 

 

Edited September 5, 2023 by umiq88

[ProDave]

9 minutes ago, umiq88 said:

I'm toying with the idea of fitting ASHP instead of thermal solar if its cheaper and switching between the two based on current price.

If you are considering solar thermal (a one trick pony) you obviously are happy with something on the roof.  So fit solar PV.  It will power anything that is using electricity in the house and if there is more generation than use, it is easy to dump the surplus to water heating.

 

Most of us that do that have very low water heating costs in the summer, and lower electricity bills.

 

An ASHP then makes better sense as it is yet another easy way to use some of that self generated solar PV.

 

My ASHP was an ebay purchase for under £1K but you can get new for about £3K upwards.  No harder to fit, in fact I would say easier to fit that an oil boiler, no storage tank, no servicing and no volatile cost fuel.  While I agree oil may be cheaper now, it is a very volatile price, so may not always be so.

[JohnMo]

17 minutes ago, umiq88 said:

Do you mind sharing your model and supplier?

Good old Ebay purchase. Mine is a 6kW Maxa heat pump. Like @prodave says super easy to install two pipes, one to a 3 way diverter valve the other is the returns to ASHP.

 

27 minutes ago, umiq88 said:

I'm talking average efficiency over the year. Your heat pump is not going to achieve 400% in the height of winter when you need it the most.

Height of winter no they will not achieve 400%, but overall they can and do.  The advertised SCoP for my heat pump at 35 deg flow temp is 4.26.

 

However CoP at 2 deg and 30 flow temp is 4.26. While at 7 deg a flow temp of around 26 will give a CoP of nearly 6.  Add into the mix solar PV and that is offsetting running costs throughout summer and some summer months.  I know solar thermal will make your DHW, but PV is making my hot water and providing cooling and offsetting my daily running costs for electric. In fact since the ASHP install, my electric bills during the summer are unchanged from last year (no ASHP last year - installed May 23). This year I am also running cooling (through UFH pipes) via the heat pump most sunny days for 6 to 8 hours, the equivalent of CoP for cooling, is around 6 while cooling, but PV is supplying the electric, so zero running cost.

 

43 minutes ago, umiq88 said:

most efficient in summer you don't need the heating and for hot water it can't reach the 60degrees required.

 

My immersion has taken my cylinder up to 80 the last couple of days, via the PV diverter, heat pump hasn't done any DHW heating.  Even if you store water at 46 degs, they only recommend you heat to 60 weekly, this can easily be done by immersion, but its questionable if you really need to in the UK, unless you have immune system issues.