How to size boiler/system correctly for Passive house.

Do-more

I'm about to build a new house which will have near passive levels of insulation so my heating requirements will be quite low. I have enquired about stoves and boilers from a number of suppliers but I would like to independently calculate what will satisfy my requirements so that I am not at the mercy of suppliers telling me their solution is best when it may not be.

The total space heating demand for the house is estimated at 4,450kWh and the total DHW demand is estimated at 4,177kWh by the PHPP calculation for the house.

I will install approx. 8m2 of solar panels which should provide an estimated 2860kWh of useful heat.

I am looking at installing a water jacketed wood pellet stove which is rated at 10kW which has a 80/20 split between hot water production and room heat.

While the stove is running it will radiate up to 2kW of heat to the living room. The balance of space heat demand will be added to the house via the heat recovery ventilation system which has a 2.6kW hot water after heater in it. (it's rated at 2.6kW with water at a temperature of 55d eg C so probably closer to 3.5kW with 70 deg C water ?)

I do not know what size of thermal store is best suited to such a set up, likely options are 300, 500 or 750 litres.

So the questions are, what size of thermal store should I use? and is a wood pellet stove the right choice or is a larger wood pellet boiler a better choice?

I don't have mains gas available and I would prefer not to use oil.

The monthly breakdown of space heating and DHW demand (minus solar input) is as follows for the major heating months.

Oct. 370kWh 206 SH + 164 DHW
Nov. 826kWh 565 SH + 261 DHW
Dec. 1154kWh 858 SH + 296 DHW
Jan. 1214kWh 950 SH + 264 DHW
Feb. 970kWh. 789 SH + 181 DHW
Mar. 800kWh. 702 SH + 98 DHW
Apr. 322KWh. 322 SH + 0 DHW.

I don't know if it is valid but looking at the peak month of January with 1214kWh the average daily demand would be about 40kWh which could theoretically be provided by the stove running at full output for 4 hours. So I would assume that this size of stove would be able to fulfil my demand or is that seriously flawed thinking?

Any help or advise with sizing the stove and thermal store would be greatly appreciated.

Do-more

Can no one offer an opinion on sizing a wood pellet stove correctly? :eek:

MicktheMan

Do-more wrote: »

I'm about to build a new house which will have near passive levels of insulation so my heating requirements will be quite low. I have enquired about stoves and boilers from a number of suppliers but I would like to independently calculate what will satisfy my requirements so that I am not at the mercy of suppliers telling me their solution is best when it may not be.

The total space heating demand for the house is estimated at 4,450kWh and the total DHW demand is estimated at 4,177kWh by the PHPP calculation for the house.

I will install approx. 8m2 of solar panels which should provide an estimated 2860kWh of useful heat.

I am looking at installing a water jacketed wood pellet stove which is rated at 10kW which has a 80/20 split between hot water production and room heat.

While the stove is running it will radiate up to 2kW of heat to the living room. The balance of space heat demand will be added to the house via the heat recovery ventilation system which has a 2.6kW hot water after heater in it. (it's rated at 2.6kW with water at a temperature of 55d eg C so probably closer to 3.5kW with 70 deg C water ?)

I do not know what size of thermal store is best suited to such a set up, likely options are 300, 500 or 750 litres.

So the questions are, what size of thermal store should I use? and is a wood pellet stove the right choice or is a larger wood pellet boiler a better choice?

I don't have mains gas available and I would prefer not to use oil.

The monthly breakdown of space heating and DHW demand (minus solar input) is as follows for the major heating months.

Oct. 370kWh 206 SH + 164 DHW
Nov. 826kWh 565 SH + 261 DHW
Dec. 1154kWh 858 SH + 296 DHW
Jan. 1214kWh 950 SH + 264 DHW
Feb. 970kWh. 789 SH + 181 DHW
Mar. 800kWh. 702 SH + 98 DHW
Apr. 322KWh. 322 SH + 0 DHW.

I don't know if it is valid but looking at the peak month of January with 1214kWh the average daily demand would be about 40kWh which could theoretically be provided by the stove running at full output for 4 hours. So I would assume that this size of stove would be able to fulfil my demand or is that seriously flawed thinking?

Any help or advise with sizing the stove and thermal store would be greatly appreciated.

What does 'near passive levels of insulation' mean?

You cannot heat air to above about 50 degC as the dust will burn above this temp and you will smell it in the house.

Your phpp designer is best placed to advise on specs as he/she has all the info at their fingertips.

Do-more

Thanks for the info Mick, my Architect has been on holiday but just replied to me with similar info last nigh, from the design airflow it seems that the maximum amount of heat that can be added via the ventilation system is 1.8kW.

The 55 degrees refers to the temperature of the water going to the heat exchanger, I wouldn't have though that the air temperature in the duct would be near that level but presumably the dust will burn in contact with the heat exchanger surface. Back to plan A so.

MicktheMan wrote: »

What does 'near passive levels of insulation' mean?

For the house to be considered passive the space heating requirement should be 15kWh/m2/a whereas mine is currently calculated at 22kWh/m2/a so not passive.