Heating & DHW solution sought for a new highly insulated house

[dullnote]

Hi John S the house is 2 years old, 300mm insulation in roof, walls 150mm (timber frame), in exposed site high up approx 850 feet above sea level, last year snowed in for over two week, snow on drive and road for over a month. Must be fairly well insulated as snow never moved from roof.

This was the first year in and I had all room at set temp of 21 degrees, this year looking at turning down rooms not in use to 18, also started putting LED ect the electrical is down also PV installed making a big difference from start of August this eat to end Oct used 729 last year same period 893 19% down, this will be PV and LED fitted also simple turning things off ( I know I am bad but starting to get better).

Another chart tells me converting LPG from Lt to KWH should be 6.5 not 7.08 this would give 23400KWH much the same as you. Checking Gas used so far this year and with my adjustments down 11% so far and I had to put heating on start of Sep instead of mid Sep two weeks early.

I think I am going in the right direction

Dullnote

Do you know anything about the SAP ratings?

[brackwell]

Hi,
heat loss 1.14 W/m2K  means watts per m2 of your house for every 1 deg C (k stands for kelvin -the same as C) 

So 1.14 Watts x 240 (floor area) = 273.6 Watts for every 1C the house is above outside temp.  So outside temp of 0C and inside temp of 21C  would make this 273.6 x 21 = 5.745 Kw and in 24 Hr this is 24 x 5.745 = 137.9 Kwhr per day

Most people would say this is a lot.   

I would suggest you consider turning down the thermostats because every 1C difference changes the energy requirement by 10%  If the rooms are never occupied turn them down really low and close the doors !  I know you should not have any but make sure you do not have any draughts and strong convection currents as this is one reason for people turning up the thermostat.   As i sit here my house is about 18 -18.5 with no heating on and i am wearing a pullover.

The water use is what ever you want it to be and thats another subject.

When you bought the house you would have had the energy performance certificate which is part of the full SAP energy assessment and this shows the energy rating of your house which is the 67 you mention and puts it into the top end of "D"
rating -probably about right for such a big house. See http://www.energykey.co.uk/epc.html

Ken

[KLD]

Those figures and calcs don't seem to stack up well...

590GJ per year: 1GJ = 1*10^9J; and with 1 J = 1 Ws  --> 3600 J = 1kWh; 590GJ = 164000 kWh.  


I always thought "heat loss" is a measure of  how much energy is lost through a building element of a given area per unit time per temperature difference. So, if for instance one of your windows has a U-value of 1 W/m² K and is 1m by 1m in size, then the heat flow (i.e. energy per time, units J/s = W) is P = 1 W/m² K * 1m² = 1 W/K.
If the average building heat loss coefficient is 1.14W/m² K, then you need to calculate the total area of all walls and roofs (and floor? not sure) to be able to calc the heat loss rate. Say your house had a footprint of 10m by 12 m, and a height of 5m with a flat roof, then the total area would be (10+12+10+12)*5m² (for the walls) plus 12*10m² (for the roof) plus 120m² for the floor. Total area is then 460m². At the design outside temperature of -1°C, room temperature 21°C, i.e. temp difference 22K, then your total heat loss rate is P = 1.14W/m² K * 460m² * 22 K = 11.5kW.
For an almost new house that figure seems rather too high.

Klaus

Edit: the design outside temperature is valid for the walls and roof, while the floor "sees" a heat sink (e.g. the soil) at a different temperature. Can someone else confirm or otherwise whether how the floor is treated in SAP?

[brackwell]

Klaus,

You are correct but i think dullnote is referring to item 38 on the sap2005 form  which is "heat loss parameter W/m2K" which seems to be derived in the manner you describe but then divided by the floor area. 

Dullnote,

Are your walls only 150mm wide of wood construction.  I am no builder but that does not sound a lot for a new house?

Ken

[ecogeorge]

 Quote -

dynamics of our system are:

Water in at 23c
Floor at 21c
Room at 18.5c

One of the idiosyncrasies of UFH is that if you heat the room to the temperature you'd feel comfortable with with radiators (say 21c or 22c for a living room) it feels too warm and too stuffy.

I can't recommend UFH enough. And if you are anywhere near GL15, you're more than welcome to pop over for a coffee and take a look.
[/quote]

Do you really keep a room at 18.5 whilst running the uf water temp at 23c ? Do you run heating continuously to achieve this?
Have you a large buffer tank to prevent cycling?
Run my floor water temp @ 33c - but is not on continuously-too tight so wait until woodburner lit or very cold then gshp turned on.
Also GL15    

[dullnote]

Hi KLD I built the house myself (well my wife and myself three years hard labour), to be honest when I got the SAP report handed it to Building Control and never looked at it so much else going on, only not with reading these forum thought I dig it out and see what it means.

I have had a look at the calcs for "Heat Losses and heat loss parameter" it goes through all walls, floor, windows works out m2 works out heat loss made up of a factor ( windows only) * area * u value end up in W/K add all these up and it come to 339.79 w/K then heat loss parameter is 339.79/floor area 240.4 = 1.41 W/m2K.

Looking at the cals the area of all outside walls, roof and floor comes to 580m2 using your calc for 22 degree difference comes to 12.77KW but reading brackwell it would be 5.745KW.

Getting some but also getting confused,.

Reading more of the calcs notice average u value is 0.39 W/K/m2 to get this to KW would this not be *22 K * outside surface area 580 m2 = 4.976 KW

Both of these dont match with the 590GJ but we can get to that sometime.

Regarding floor yes these are included in SAP the ground floor in mine has u value of 0.20, and the floor above garage u value of 0.26.

Hope this helps It is starting to make sense to me I think, still not sure the heat loss parameter is the right figure to use in the calcs.

Thanks All

Dullnote (bed time)

Sorry writing this and your replies came in wall average u value 0.318 roof average u value 0.19 mentioned the floors above.

I think part of the problem is the boiler is on and off every 10 mins only stayed on during really cold spell, I spend more time pumping cold water around my floor, something not right, hence starting to look at things

[dhaslam]

The hard part to calculate is the effect of passive heat.    A heat loss calculation based on the u-value of walls etc gives you the heat loss in the dark  with no appliances running.   If you have appropriate windows, south facing mainly and shaded from direct summer sun,   the actual heat requirement is greatly reduced probably by more than 50%.  Of course the thermostat setting become  very important because the reduction is mostly made in the temperature range that needs auxiliary heating.     Something that is not always emphasised  about extra insulation, is that if you double the insulation  in a house that  is insulated to  say 1980s standard  the fuel saving is likely to be 75%.

[Richard Owen]

Do you really keep a room at 18.5 whilst running the uf water temp at 23c ? Do you run heating continuously to achieve this?
Have you a large buffer tank to prevent cycling?
Run my floor water temp @ 33c - but is not on continuously-too tight so wait until woodburner lit or very cold then gshp turned on.
Also GL15    

Yep, those are the numbers.

Heat pump runs for E7 hours unless very, very cold when it goes on for a couple of hours in the late afternoon.

Heat pump produces water at 30c. This goes directly to UFH in bathroom and towel rails.

Blend valve takes it down to 23c for the Kitchen UFH.

Did have buffer tank but it didn't prevent cycling.

Have now taken tank out and put up with cycling (not that we notice, heat pump is in the garage and runs when we're in bed.)

[KLD]

(...) 33KW LPG boiler (...)

Could this be part of the issue? How efficient is this boiler under part load? There will be very few days when you need 33kW for space heating.

Klaus

[brackwell]

Perhaps the LPG boiler does not modulate !?

My heat loss parameter is 1.32 W/m2 K  so dullnotes 1.41 seems in order.  Your/My 5.745 Kw ie 138 Kwh/day for a non lived in house seems about right. (your boiler on for 4 hrs a day)

This heat loss parameter only takes account of fabric heat loss and ventilation heat loss.

Later comes the effects of water heating losses , solar gain and people just occupying the building.  You may be contributing 15Kw/day from your use of electricity. Your solar gain on a good day could be half your requirement.

Turn the thermostat down to 18C and save 30% or more.

I still think those walls are thin.

Ken

[dullnote]

Hi I am putting a wood burning stove in the living area hope this helps ( fitting for heat and because it looks good) was speaking to Building control today as they phone to confirm all is OK asked about insulation, I can not put in cavity wall as the house is timber kit house, but can increase loft and eaves ( house is 1 and 1/2 stories ) as long as I keep the 50mm air gap. I think this will help as I was in the eaves during the spring and it is gale force wind coming in and at that point only 100mm of insulation.

The boiler is set between 1 and 2 dial goes up to 7 boiler on for about 4 hours a day at present, you hear the boiler trying to reduce the gas use but the temp still goes up and the boiler switches off.

I am heading down the road of more insulation where ever I can, turn the heat stats down a degree or so, more depending on log burner, and have a good look at the boiler and controls.

Klause I have never had the boiler up above 3 and this was when the we were in arctic conditions, and the heating was only on I think for about 8 hours a day, don't know about efficiency at part load will have to go and look.

Thanks

Dullnote

[brackwell]

Dullnote,

The SAP type calculations assume 0C outside and therefore bear no resemblance with what you are seeing today. 

Opinion is divided but i am not a advocate of the idea of leaving the boiler switched on.  My approach is to use the boiler hard for a fixed time in the morning say 1 hour and maybe or not another burst later in the day if conditions require it. Cycling boilers or those working at low power are bad news.