What sized ASHP

[Happy Valley]

I have been provided with the following information as part of the SAP for our 160 sq m new build:

 

This is the initial draft for the design

• Summary of input data
• Basement floor and Ground floor 0.13W/m²K
• Basement wall and Main wall 0.2W/m²K
• Roof 0.13W/m²K
• Thermal bridging - used ICF details and PSI values where possible
• Windows u value 1.4W/m²K G factor 0.63
• Doors u value 1.4W/m²K
• Ventilation MVHR Envirovent energiSava 380 extract to Kitchen + 4 other rooms (assumption only because the SAP default is not compliant with building regs. this can be updated when the proposed is known)
• Air tightness 4.0 m³/hm² (I have kept this quite low because it enhances the MVHR performance and ICF is naturally air tight)
• Main heating, Generic ASHP supplying underfloor heating with time and temperature zone control. Design flow temperature 35ºC
• Secondary heating - none
• Water heating - 250 litre cylinder with losses of 1.67 kWh/day from heat pump
• 100% low energy lighting

 

With this information is there a way of working out what sized ASHP is required?

[JamesP]

Couple of threads here.

 

 

 

[PeterW]

51 minutes ago, Happy Valley said:

I have been provided with the following information as part of the SAP for our 160 sq m new build:

 

This is the initial draft for the design

• Summary of input data
• Basement floor and Ground floor 0.13W/m²K
• Basement wall and Main wall 0.2W/m²K
• Roof 0.13W/m²K
• Thermal bridging - used ICF details and PSI values where possible
• Windows u value 1.4W/m²K G factor 0.63
• Doors u value 1.4W/m²K
• Ventilation MVHR Envirovent energiSava 380 extract to Kitchen + 4 other rooms (assumption only because the SAP default is not compliant with building regs. this can be updated when the proposed is known)
• Air tightness 4.0 m³/hm² (I have kept this quite low because it enhances the MVHR performance and ICF is naturally air tight)
• Main heating, Generic ASHP supplying underfloor heating with time and temperature zone control. Design flow temperature 35ºC
• Secondary heating - none
• Water heating - 250 litre cylinder with losses of 1.67 kWh/day from heat pump
• 100% low energy lighting

 

With this information is there a way of working out what sized ASHP is required?

That’s a pretty crap window score - most modern UPVC hits 1.0 without a huge issue so why go with a lower performance ..??

 

Basement/ground  floor is too high as well - get them to 0.11 or 0.1 using slightly better insulation and you will get much better SAP score and lower run costs. 

[SteamyTea]

ACH is poor to.

[SteamyTea]

1 hour ago, Happy Valley said:

With this information is there a way of working out what sized ASHP is required

Yes

get some local weather data and it becomes easy

 

 

 

[Happy Valley]

2 hours ago, PeterW said:

That’s a pretty crap window score - most modern UPVC hits 1.0 without a huge issue so why go with a lower performance ..??

 

Basement/ground  floor is too high as well - get them to 0.11 or 0.1 using slightly better insulation and you will get much better SAP score and lower run costs. 

 

Thanks for your input.

 

Since this was done I have a quote for Velfac windows with a U of 0.79 to 0.82.

 

Shall discuss the ground floor with the architect. 

 

 

[Moonshine]

2 hours ago, SteamyTea said:

get some local weather data and it becomes easy

 

what sort? monthly averages?

[J1mbo]

degree days

[SteamyTea]

2 minutes ago, Moonshine said:

 

what sort? monthly averages?

Daily if you cannot find hourly.

Ideally Temperature, Solar, RH, Windspeed and Direction.

[Iceverge]

Without know the various areas of your windows walls and doors it's impossible to say. 

 

A 160m2 bungalow has a far greater surface area than a 2.5 story cube. 

 

Either that or forego the ASHP at build stage. Install a wills heater and monitor it for a year. You'll know exactly then. 

[ProDave]

You don't need a whole years worth of data do size an ASHP.  You just need to know the buildings heat loss at the coldest temperature you expect to have to deal with in a normal winter.  I based that on -10 outside for where we live.  The heat loss is so low, the smallest ASHP we could find gives twice the amount of heat we need even in the depths of winter.

[J1mbo]

Quick calc suggests required DHW reheat time is likely to be the key sizing requirement for this property.

[Happy Valley]

18 hours ago, Iceverge said:

Without know the various areas of your windows walls and doors it's impossible to say. 

 

A 160m2 bungalow has a far greater surface area than a 2.5 story cube. 

 

Either that or forego the ASHP at build stage. Install a wills heater and monitor it for a year. You'll know exactly then. 

 

House is stepped up a slope but about 98 sq m is effectively at ground level.

 

The wills heater intrigues me and if we can get the U values down enough will certainly consider it. Do they have a maximum floor area for UFH?

[Iceverge]

you can add more than one if needed. your peak heating load is what you’re after. there’s a good spreadsheet here somewhere if you search for it. 

[Moonshine]

45 minutes ago, SolarSunScott said:

I have an MCS spreadsheet I can email you. I inboxed you my email

 

 

do you mind sending it to me?

[Moonshine]

3 minutes ago, SolarSunScott said:

what is your email address?

 

 you can send the excel file via the forum message service