Deleted 6 December 2022 at 11:09AM edited 12 January at 10:56PM in Green & ethical MoneySaving 35 replies 1.2K views

[Deleted User]

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zeupater

Hi

Two degree drop in temperature since you got up? ... you probably need more insulation ...

We're well insulated, resulting from an efficiency project that's been going on for over 25years, but our approach was to model existing building structure materials in a spreadsheet (U-Values etc) in order to evaluate theoretical heat-loss, check the values against historical actuals and update/tweak the model until it was pretty accurate, then use this as a baseline to plan & cost improvements on a strict ROI basis ... just checked the spreadsheet & it was last updated in 2014 ...

If you take this approach then you'll find that it's often the small, cheap & easy jobs (low hanging fruit) that will have the most effect, so you're probably looking at draught proofing doors, loft hatches, letterboxes etc then where pipes/cables push through walls/ceilings ....

As you're in a bungalow, you've likely got a larger ratio of ceiling to wall area than a multi-storey property, so the biggest energy efficiency improvement will be to stop the heat escaping upwards ... we had the standard ~100mm loft insulation so added ~200mm to update to current standards, then later added another ~200mm because the model still showed potential savings high enough to warrant the expense ... it's probably the best area for investment because it worked & contributed the most to enabling the home to be as thermally efficient as it is whilst still being comfortable ...

Our house has high thermal mass, not only the shell of the building, but also in the internal structure ... the walls around the internal fireplace were designed with additional thickness to act as a massive heat store, as such it takes ages to raise or lower the internal temperature, which can be seen as good to smooth temperatures both in summer & winter, however, failing to top-up the heat can result in needing to run heat sources for extended periods over a number of days before the thermal mass is recharged to a decent level and temperature is maintained at a comfortable level ...

Currently, it's 3C outside with a forecast of -2C overnight, we've had the log burner running once (after sweeping the chimney) and since last winter we've used ~45kWh of gas to top up the solar thermal & we're currently importing ~6kWh of electricity from the grid per day against an annual average of ~3.5kWh/day ... current total house load is around 360W, including TV & heating to maintain 19C ... if the forecast is correct & it's actually sunny tomorrow the heat pump will be tasked to convert the PV collected energy into stored thermal as quickly as it's able ... make heat while the sun shines!

HTH - Z

Coastalwatch

My Zeup, 6 kWh's seems an incredibly low import figure for this time of year, ours has been closer to 35! Presumably consumption has been somewhat higher! Only, with Solar generation being rather limited this time of year, I wonder if it's solely down to air tightness/insulation or if you've another energy source making a contribution aside from that of the grid?

Screwdriva

We just spent £500 today to insulate the area immediately above our main entrance door. 100mm rockwool everywhere + 100mm insulation between rafters (pictured) + expanding foam in all the gaps. As it turns out, this area was hollow, lacking any insulation and was externally facing, essentially acting as a cold air funnel into the front mid level flooring of our semi-detached. That small part of the house was always freezing. 

Was it worth it? Who knows....but the shower room immediately above is no longer unbearable and the adjacent rooms  feel less cold and damp. The Viessmann is modulating even lower than before, so perhaps it will be one day. Today however, the home is definitely more comfortable.

ABrass

Others experiences are worthless to you. You need to know the details of what has been built.

What roof insulation do you have, how are your walls insulated?

The rule of thumb is that loft insulation is best value, followed by walls, then floors then windows. But unless you know what is in place you'll never work out the cost of the next steps or the difference they'll make.

Magnitio

Dropping from 24 degrees to 12 degrees in 10 hours is significant, even with a temperature of -4 outside. As a comparison, our house dropped from a max of 18.7 at 19:00 yesterday to 15.1 at 06:30 this morning with no heating in a 1970's detatched house. It may have only been a minimum of -1 outside though.

I would suggest buying/renting a thermal imaging camera to identify where you're losing heat.

ABrass

You used around 30-50kW of heat (depending on how hard your log burner is working). You're probably burning 37.5-90kWh of fuel. That's not terrible for some very cold weather but it isn't award winning.

Your usage is unusual enough that direct comparisons aren't easy. You aren't fully heating all the house all day, so direct comparisons to a centrally heated building are much  harder.

Without knowing what you have working out what the economic next steps are is, obviously, impossible.

QrizB

Deleted_User said:

So really - our insulation isn't bad in the least. It's a warm house - it was also a warm house when we used gas CH. I just want to get an idea of what's possible with latest technologies.
...
As I've said, I know what I have.

Is your house of traditional construction, or something more modern?

We've got a 1950s semi with brick cavity external walls and single brick internal walls. all those bricks give us a lot of thermal mass.

Back-of-an-envelope and subject to revision, I think our walls contain around 50 tonnes of bricks which gives a heat capacity of roughly 11kWh / deg. C. So for each degree C that pur house cools, we'll be losing 11kWh of heat.

If your house is eg. wood-framed, or made with lightweight block, you'll have a lot less thermal mass. With equivalent insulation it will cool more quickly.

ABrass

If you retrofit to Passivehaus standard your heating bill will be virtually zero. Solar gain and the heat of people in the house balance loss to the outside world.

ABrass

Of course there's diminishing returns. You're probably there already.

Potential gains wise you're probably close to the Umea example: https://www.sciencedirect.com/science/article/pii/S1876610216307548

Costs depend on what you have, and you know what you have.

chris_n

Looking at U values for building regs so minimum standards. Something built to Passivhaus specs would be a lot better.

           2000. 2022

Walls. 0.45. 0.18

Roof. 0.35. 0.11

Floor. 0.51. 0.13

Windows 3.1. 1.2

All figures are in Watts per square meter per degree difference in temperature either side of the element. 

So assuming in internal temp of 20 and 0 outside a1m2 window to 2000 spec would constantly loose 62W of heat energy, a 2022 spec window would loose 12W.

The same calculation for 10 square meter wall would be 90W for a 2000 spec and 36W for a 2022.