First time new build

[Risemead]

We are starting our new build project very soon, its around 590 sqm project. We have gone through various options for heating like Borehole heating, Airsource, Ground source and finally decided to go with two boilers. I just couldn't justify the installation cost of these three and the running cost for  ASHP & GSHP is almost 75% of the boiler running cost, so cant see where we save anything. Any suggestions? Definitely going ahead with the MVHR.

[IanR]

Hi and welcome.

 

How about reducing the energy/heat losses of the building so that you don't need such a large (two boilers?) heating system.

 

Are you saying you have calculated a heat pump to be 75% more day-to-day running costs than a fossil fuel boiler? or are you saying 25% less?

 

Day-to-day running costs should be around the same.

[nod]

We also looked at GSHP and dismissed for similar reasons 

We also dismissed PV for the same reasons 

Plus it looks awful 

ASHP will always be more expensive to run than gas 

But 75% more is way out 

We have a gas boiler and UFH on our first build Running costs are low Certainly for heating 

I would be looking more towards boosting insulation levels 

[JohnMo]

If you are having to install two boilers you really do need to look the thermal properties of the building.  Or rerun the heat calculations.  If you are installing MVHR you are obviously taking airtightness seriously (or hope so), so I assume you have thought about the insulation also.

 

Even though your building is massive, just over three times our build, we could still heat it with the gas boiler installed in our house.  If your heat loss at -3 degC is more than 10kW you need to work on insulation, windows etc.

 

 

[IanR]

23 minutes ago, nod said:

ASHP will always be more expensive to run than gas 

 

With Gas prices now having gone up by a higher percentage than electricity prices, ASHP v. Gas boiler day-to-day running costs are now in parity, or slightly in ASHP's favour.

[nod]

8 minutes ago, IanR said:

 

With Gas prices now having gone up by a higher percentage than electricity prices, ASHP v. Gas boiler day-to-day running costs are now in parity, or slightly in ASHP's favour.

Electricity prices will simply track gas price 

Most of our power stations run off fossil fuels 

If ASHPs ran off fresh air 

There would be a tax on fresh air

Id expect ASHPs to be about 20% more expensive to run than gas 

 

[JohnMo]

You would need an overall COP of 4 to be on running cost.

 

Gas 7p electric 30p per kWh

[IanR]

7 minutes ago, nod said:

Id expect ASHPs to be about 20% more expensive to run than gas 

 

But they're not. My local gas standard rate is 7.37p and Electricity is 28.34p

 

Gas boilers are, say, 90% efficient. An ASHP needs a SCOP of 3.46 to be in parity. For me, ASHP is cheaper to run day-to-day, even without considering not having to pay the gas standing charge.

 

Inflationary pressure will remain higher on gas than electricity going forward, for many reasons. Over time the swing will be more in favour of electricity.

Edited May 13, 2022 by IanR

[Risemead]

1 hour ago, IanR said:

Hi and welcome.

 

How about reducing the energy/heat losses of the building so that you don't need such a large (two boilers?) heating system.

 

Are you saying you have calculated a heat pump to be 75% more day-to-day running costs than a fossil fuel boiler? or are you saying 25% less?

 

Day-to-day running costs should be around the same.

This is the quote I had for heat pump: 

Total electricity consumption 13277 kWh / yr
Estimated Heat Pump fuel cost £3,757
Estimated fuel cost for boiler £5,043 per year

[Risemead]

and the installation cost was around £25k

[Risemead]

56 minutes ago, nod said:

We also looked at GSHP and dismissed for similar reasons 

We also dismissed PV for the same reasons 

Plus it looks awful 

ASHP will always be more expensive to run than gas 

But 75% more is way out 

We have a gas boiler and UFH on our first build Running costs are low Certainly for heating 

I would be looking more towards boosting insulation levels 

Total electricity consumption 13277 kWh / yr
Estimated Heat Pump fuel cost £3,757
Estimated fuel cost for boiler £5,043 per year

[JohnMo]

To quote you they will have done a heat loss calc, what are you u values for wall floor and roof, how do they compare with your architect drawing?

[IanR]

13 minutes ago, Risemead said:

Total electricity consumption 13277 kWh / yr

 

Is that space heating and water? For a GSHP they may have used a SCOP of 4.5, which would mean a roughly 60,000kWh annual energy requirement for heat and hot water.

 

Unless you are providing hot water for 10, or have included a swimming pool, you could easily get that figure down to sub 20,000kWh annual energy requirement.

 

12 minutes ago, Risemead said:

and the installation cost was around £25k

 

GSHP install cost do not make the small efficiency increase over ASHP worth it.

 

An ASHP install cost should be in the region of £5K to £10K more than the equivalent gas install, and you can get £5K back in a BUS grant.

Edited May 13, 2022 by IanR

[Risemead]

not sure, i am not a techie, its a flat roof building with UFH throughout. 

[Risemead]

12 minutes ago, IanR said:

 

Is that space heating and water? For a GSHP they may have used a SCOP of 4.5, which would mean a roughly 60,000kWh annual energy requirement for heat and hot water.

 

Unless you are providing hot water for 10, or have included a swimming pool, you could easily get that figure down to sub 20,000kWh annual energy requirement.

 

 

GSHP install cost do not make the small efficiency increase over ASHP worth it.

 

An ASHP install cost should be in the region of £5K to £10K more than the equivalent gas install, and you can get £5K back in a BUS grant.

I will need two heat pumps to cover the whole building, if it was smaller then you are correct. With the size of around 590 sqm, one is not enough and when we go for two the cost goes up and cant see if I can ever recover the cost. 

[IanR]

4 minutes ago, Risemead said:

I will need two heat pumps to cover the whole building, if it was smaller then you are correct. With the size of around 590 sqm, one is not enough and when we go for two the cost goes up and cant see if I can ever recover the cost. 

 

Simple, cost effective steps could vastly improve your proposed building's energy efficiency.

My property is a modest ~450m². But, as a barn conversion, has a large volume, circa. 1650m³.  That would be similar to yours if you had an average 2.8m ceiling height. My space heating and hot water could be comfortably met with an 8kW ASHP. I did oversize my heat pump to 12kW, wanting a faster re-heat on the hot water, but that has proved entirely unnecessary.

 

My annual space heating requirement is around 6,400 kWh. Hot water is around 10,000kWh, which combined, needs around 4,000kWh of electricity at a SCOP of 4.

[jack]

23 minutes ago, Risemead said:

I will need two heat pumps to cover the whole building, if it was smaller then you are correct. 

 

Size isn't everything. Our house is almost exactly half the size of yours with very high ceilings (so large volume), and we comfortably get by with a 5kW ASHP given our insulation and airtightness levels.

 

I have no idea who's done your calculations, but even a 590 m² house should comfortably be heatable with a single ASHP assuming you go for reasonable insulation and airtightness (the latter being increasingly important to energy consumption as the volume of the building increases). 

[SteamyTea]

Two things.

Have the people who have quoted you just used default insulation levels for the UFH i.e. 70mm of insulation?

Have they used a default power per square metre number i.e. 25W.m^-2

 

Generally, larger buildings take less energy, on a metre squared basis, than smaller ones.

 

With a building that size, you can get a lot of PV on the flat roof, that would offset a lot of the running costs.

[Risemead]

2 minutes ago, jack said:

 

Size isn't everything. Our house is almost exactly half the size of yours with very high ceilings (so large volume), and we comfortably get by with a 5kW ASHP given our insulation and airtightness levels.

 

I have no idea who's done your calculations, but even a 590 m² house should comfortably be heatable with a single ASHP assuming you go for reasonable insulation and airtightness (the latter being increasingly important to energy consumption as the volume of the building increases). 

please let me know if you have anyone who can quote me, I can try before completely ruling out. I would prefer something other than boiler but if they are not hugely expensive to install/run. 

[Risemead]

7 minutes ago, SteamyTea said:

Two things.

Have the people who have quoted you just used default insulation levels for the UFH i.e. 70mm of insulation?

Have they used a default power per square metre number i.e. 25W.m^-2

 

Generally, larger buildings take less energy, on a metre squared basis, than smaller ones.

 

With a building that size, you can get a lot of PV on the flat roof, that would offset a lot of the running costs.

[IanR]

55 minutes ago, Risemead said:

please let me know if you have anyone who can quote me,

 

It's not about who is quoting you. It's about the property's space heating requirement being 57,225 kWh. On your property, with cost effective measures, you could get this down to around 8,500kWh.

 

Whether it's heated by gas or electricity, the property needs the same amount of heat energy inputted to maintain the required temperature. 

 

A 90% efficient gas boiler(s) will meet that requirement with 63,583kWh of gas, or an 481% efficient GSHP will meet it with 11,897kWh of electricity..

 

@ 7.37p per kWh of Gas and 28.34p per kWh Electricity, the heat pump will be cheaper to run day-to-day, but if you design, engineer and build better and get the 57,225 kWh energy requirement down to 8,500kWh both options would be much cheaper to run and install.

 

I believe there is around a £2,750 per year cost save by improving the energy efficiency of your house.

 

The parts of the build that improve energy efficiency should have a 50-60 year life, but even if you only considered a 25 year life then that's a £68,750 budget for energy efficiency measures.

Edited May 13, 2022 by IanR

[jack]

33 minutes ago, Risemead said:

please let me know if you have anyone who can quote me, I can try before completely ruling out. I would prefer something other than boiler but if they are not hugely expensive to install/run. 

 

I can't recommend anyone, but given the amount of money involved, I'd be looking at getting at least a handful of quotes to compare.

 

One problem you'll likely face if do go the low-energy route (and if you're building a house of almost 600m² and are concerned about energy costs, you certainly should!) is that lots of suppliers don't have experience with low-energy houses. They make bad assumptions about insulation U-values when modelling heating requirements, for example, but also don't have any gut feel for how such houses work in practice. Our plumber, for example, insisted that anything less than a 12kW ASHP was going to take so long to heat the hot water that the house would cool down and we'd get cold. But our house only drops a degree or so in 24 hours, so not having the heating on for an hour or two while the tank recharges makes no perceptible difference to the house temperature.

 

As a minimum, you might also want to think about what sort of U-values for walls, ceiling, and floors you want to aim for, as this will inform the heating design parameters.  

[Iceverge]

The shape of the house can make a big difference. If you have just BRegs minimum insulation and the design is, for example a series of interconnected cottages with lots and lots of external wall area, your figures might be correct. 

 

Given the scale of your energy bills I echo those above and advise you to get some advice from someone with experience in low energy buildings. It's likely their input would pay back in under a year. Someone with passivhaus credentials would probably be a good place to start. 

 

Alternatively if you post your plans on here (deidentified of course) there's plenty of knowledgeable heads who would be able to contribute further. 

 

In any case, fossil fuels costs will remain high now apparently due to speculative investment deserting the sector (so YouTube tells me?!!!) and the electricity energy mix will become less linked as the grid decarbonises theoretically swinging the price in favour of elec long term.

 

We'll see.........