Oil usage and micro hydro content

[Lesgrandepotato]

I’ve been tracking (loosely) our oil usage to get a feel for what our energy demand is, the idea being to supplement the oil with a pico hydro rig over the winter months when the beck is flowing well. 

 

So, it’s April. I’ve just filled up with 500l of oil. Our last fill up was late Nov/ early Dec I reckon that means we’ve used 600l of oil in that period. 

 

So that would suggest an annual usage I’d say about 1200l. 

 

I think a litre of oil contains 11kwh of energy? Assuming say an 85% system efficiency. That would suggest I’ve used 13200kwh * .85 of heating energy for the year. So about 11000kwh. 

 

The house is an updated 70s build circa 2500sqft + internal garage unheated. 

 

Do those figures sound about right?

[Ed Davies]

Yes, they sound plausible. The 11 kWh/litre is probably a tad optimistic but given the other guestimating (e.g., of the efficiency and extrapolation to annual usage) it doesn't really matter. How does filling up with 500 litres lead to you reckoning you've used 600 litres?

 

Here's my similar estimate: Burning Oil . 1 kWh = 3.6 MJ

 

Why estimate annual usage if you're wonder what a beck which runs mostly in winter will contribute? Wouldn't it better to compare with just winter usage, anyway?

[epsilonGreedy]

1 hour ago, Lesgrandepotato said:

Do those figures sound about right?

 

 

Nope for 2 reasons.

1. The annual KwH consumption figures for a 160 sqm model house built to 1975, 2013 and Passive standards are 56,000, 18,000 and 5,000 for space heating and hot water. Given the mixed thermal heritage of your larger house 13,200 looks like an underestimate.
2. I lived in a 2500 sq ft house for 3 years, it was built in 1900 and extended in the 80's and 90's. We consumed 3000l of oil annually. 

[Jeremy Harris]

There's no way that you can just make an assumption that a house of a given date and size will have any particular energy usage; the whole concept of trying to use just those two parameters alone is deeply flawed, for several reasons.

 

• Heat loss doesn't vary linearly with house size, as there there is a surface area to volume ratio effect that creates non-linearity (the elephant versus mouse effect). 

• One of the most significant causes of heat loss in houses is airtightness, or lack of.  A house with open fireplaces and sash windows will lose a lot more heat than the same size house with no fireplaces and casement windows, for example.

• Shape and number of storeys has a significant impact on heat loss.  Long, thin houses lose more heat than square houses.  Single storey houses lose more heat than multiple storey houses.  Detached houses tend to lose more heat than semi-detached or terraced houses.

• Window size dominates fabric heat loss, so a house with large areas of glazing may lose many times more heat than the same size of house with smaller areas of glazing.

There are many other variables, too, but the above alone will cause very large errors if only trying to use age and floor area to predict heat loss.

 

[epsilonGreedy]

@jsharris Those are all factors but at the end of the day it is odd that a 1970's house with some unspecified improvements requires 30% less heating than a 2013 standard house that is 30% smaller and also an efficient rectangular box. A 2013 house is 2.7 times more thermally efficient than an unimproved 1975 house

 

The explanation is most likely an arithmetic error by the OP or some human factor such as the OP being happy living in a house at 16 degrees or the upgrades to the house were more like a complete renovation and insulation upgrade.

Edited April 18, 2019 by epsilonGreedy

[Jeremy Harris]

10 minutes ago, epsilonGreedy said:

@jsharris Those are all factors but at the end of the day it is odd that a 1970's house with some unspecified improvements requires 30% less heating than a 2013 standard house that is 30% smaller and also an efficient rectangular box. A 2013 house is 2.7 times more thermally efficient than an unimproved 1975 house

 

The explanation is most likely an arithmetic error by the OP or some human factor such as the OP being happy living in a house at 16 degrees or the upgrades to the house were more like a complete renovation and insulation upgrade.

 

 

I think that your source is flawed, I'm afraid.  The very broad assumptions you've quoted from it leads me to doubt it's accuracy, so any broad statement, like "A 2013 house is 2.7 times more thermally efficient than an unimproved 1975 house" is probably way off the mark, and at best a very broad average across a large number of widely different houses.

 

I gradually improved our last house (a block and brick bungalow built in 1982) and by tripling the thickness of loft insulation, having CWI installed, installing reasonable uPVC double glazing and spending some time going around sealing up air leaks, managed to just about halve the heating requirement.  The biggest single improvement was from improving the airtightness, which comes as no surprise, given the high heat losses associated with air movement and ventilation.

 

As an illustration of the proportion of heat loss from ventilation, the plots below are for our current house, with and without MVHR (MVHR recovers around 80 to 85% of the heat that would otherwise be lost from ventilation):

 

[epsilonGreedy]

@jsharris your post and graphs offer nothing to disprove the assertion that a 2013 standard house is 2.7 times more thermally efficient than a 1975 house.

 

My "flawed" source is the House Builder's Bible with a table of detailed thermal calcs that show a more detailed assessment than your spreadsheet offers.

 

The relative difference of typical U-values between 1975 and 2013 for roof, walls and floors were x4.4, x6.8 and x3.8. Given the massive relative improvements in standard insulation practices I am not sure what prompts you to deride my 2.7 times improvement that I lifted from the book?

 

[Jeremy Harris]

18 minutes ago, epsilonGreedy said:

@jsharris your post and graphs offer nothing to disprove the assertion that a 2013 standard house is 2.7 times more thermally efficient than a 1975 house.

 

My "flawed" source is the House Builder's Bible with a table of detailed thermal calcs that show a more detailed assessment than your spreadsheet offers.

 

The relative difference of typical U-values between 1975 and 2013 for roof, walls and floors were x4.4, x6.8 and x3.8. Given the massive relative improvements in standard insulation practices I am not sure what prompts you to deride my 2.7 times improvement that I lifted from the book?

 

 

Assuming that a very broad generalisation from a book, derived from averaged data for a wide range of houses, will apply as a definite ration to a house built in 1975 to a house built in 2013, is deeply flawed.  It's extrapolating from an averaged data set for a wide range of different houses and assuming that it applies as a general concept to any house built in these two periods.

 

It's very dodgy to assume that even the U values quoted are definitive for houses built in those years, for a host of reasons, not least of which is that many mass housebuilders have been pretty openly flouting building regs requirements for many years now.

 

Lifting an averaged figure from a book, then applying it as if it were a defined value, doesn't stand up to scrutiny.  It may well be useful in the very broadest sense, to get a very rough idea of the sort of average performance of houses built in those periods, but will not apply to any specific house with any degree of accuracy, for reasons that are obvious when you look at the distribution of the source data, and in particular, the wide variation between the best and the worst houses for any given period.

[Lesgrandepotato]

1 hour ago, epsilonGreedy said:

@jsharris Those are all factors but at the end of the day it is odd that a 1970's house with some unspecified improvements requires 30% less heating than a 2013 standard house that is 30% smaller and also an efficient rectangular box. A 2013 house is 2.7 times more thermally efficient than an unimproved 1975 house

 

The explanation is most likely an arithmetic error by the OP or some human factor such as the OP being happy living in a house at 16 degrees or the upgrades to the house were more like a complete renovation and insulation upgrade.

 

Ok ok, the house is heated to 19 degrees on the stats. It’s been renovated but only to a basic level of insulation. We have 60internal celotex, triple glazed windows and 500mm of earth wool in the loft. That’s a start but it’s not a huge difference from stock. 

[Lesgrandepotato]

We do have smart heating control and not insignificant sized thermal store to get the best out of the boiler. 

 

But as you say it’s hardly passivehouse specs, hence wanting to know if the figures could be about right. 

[Lesgrandepotato]

3 hours ago, Ed Davies said:

Yes, they sound plausible. The 11 kWh/litre is probably a tad optimistic but given the other guestimating (e.g., of the efficiency and extrapolation to annual usage) it doesn't really matter. How does filling up with 500 litres lead to you reckoning you've used 600 litres?

 

Here's my similar estimate: Burning Oil . 1 kWh = 3.6 MJ

 

Why estimate annual usage if you're wonder what a beck which runs mostly in winter will contribute? Wouldn't it better to compare with just winter usage, anyway?

 

All good points, we ordered 500l as we were at 50% on the gauge. It’s a 1200 l tank and it’s now 9/10ths full.

[epsilonGreedy]

3 minutes ago, JSHarris said:

Assuming that a very broad generalisation from a book, derived from averaged data for a wide range of houses, will apply as a definite ration to a house built in 1975 to a house built in 2013, is deeply flawed.

 

 

There is no average data used in these claims. The claim is based on detailed scientific thermal model that is more detailed and more useful than that offered in your own spreadsheet which by your own admission ignores that two most influential factors in house thermal modelling namely cold bridging and incidental gains.

 

As you say mainstream builders cheat when trying to meet thermal regs but this statement does at least demonstrate there is a reference point. We can take building regulations and typical building practices of an era as a base reference point for comparison.

 

The OP was asking for a sanity check on his calculations and I still maintain something feels wrong. The insulation improvements to his 1970's house would need to have been spectacular to outperform a smaller 2013 standard by a 30% margin.

[epsilonGreedy]

9 minutes ago, Lesgrandepotato said:

 

Ok ok, the house is heated to 19 degrees on the stats. It’s been renovated but only to a basic level of insulation. We have 60internal celotex, triple glazed windows and 500mm of earth wool in the loft. That’s a start but it’s not a huge difference from stock. 

 

Right so your house is actually so greatly improved it sits somewhere between a 2013 standard house and Passiv house on a performance scale. I still think using a single pair of oil tank level samples is a bit hit & miss though it might not matter for your purpose.

[Lesgrandepotato]

So working it up a bit further. Assuming I can run for 4mths a year. Taking a 1kw unit, that’s 2880 kWh. 

Its a moderate gain, but not at all dominant. So we probably need to look at pair of 1kw units. That’s circa 5.5k which based upon current back of a fag packet calcs would be of interest. 

[Lesgrandepotato]

Just now, epsilonGreedy said:

 

Right so your house is actually so greatly improved it sits somewhere between a 2013 standard house and Passiv house on a performance scale. I still think using a single pair of oil tank level samples is a bit hit & miss though it might not matter for your purpose.

I don’t know. Hence the question. I know we’ve made improvements as we’ve renovated but I have no idea how efficient a modern BR building is. I’d be surprised if we’d passed it based upon the basics we’ve done. 

[billt]

21 minutes ago, Lesgrandepotato said:

 

Ok ok, the house is heated to 19 degrees on the stats. It’s been renovated but only to a basic level of insulation. We have 60internal celotex, triple glazed windows and 500mm of earth wool in the loft. That’s a start but it’s not a huge difference from stock. 

 

Actually that looks pretty good to me, well into the realm of diminishing returns. A typical 1970s house would have 50mm of loft insulation, no wall insulation and single glazed windows. Presumably the cavities are insulated as well as the 60mm of celotex.

 

Your 1100l of oil sounds quite credible, bearing in mind that you keep the room temperatures low (a lot of people seem to like 23C+) and last winter was very mild. You might find your consumption increases significantly in a cold winter.

[Jeremy Harris]

21 minutes ago, epsilonGreedy said:

 

There is no average data used in these claims. The claim is based on detailed scientific thermal model that is more detailed and more useful than that offered in your own spreadsheet which by your own admission ignores that two most influential factors in house thermal modelling namely cold bridging and incidental gains.

 

As you say mainstream builders cheat when trying to meet thermal regs but this statement does at least demonstrate there is a reference point. We can take building regulations and typical building practices of an era as a base reference point for comparison.

 

The OP was asking for a sanity check on his calculations and I still maintain something feels wrong. The insulation improvements to his 1970's house would need to have been spectacular to outperform a smaller 2013 standard by a 30% margin.

 

 

Please explain to me exactly why I should have included thermal bridging in my simple model (which, as I've already written, was specifically designed for optimising a house without thermal bridging)?

 

If you look at some typical thermal bridging data for a detached 2013 house, built to just meet building regs, then you'll find that the Y value varies from an aggregate for all thermal bridging of around 0.19 W/m².K if the SAP default values are used, to about 0.08 W/m².K if accredited details are used (which may not be that accurate when compared to calculation for the specific details used).    It's pretty damned clear that there's more than a 2:1 range for a 2013 house, so what do you think the range would be for a 1975 house?

[epsilonGreedy]

4 minutes ago, JSHarris said:

Please explain to me exactly why I should have included thermal bridging in my simple model (which, as I've already written, was specifically designed for optimising a house without thermal bridging)?

 

 

You don't have to do anything but why do you feel entitled to mock a book that attempts to produce a more accurate model?

 

One of the most common sources of selfbuild dissatisfaction is from people who end up with thermally dysfunctional houses. Some end up buying electric panel radiators and others suffer sleepless nights in over heating properties. Selfbuilders will surely benefit from reading a book that highlights that thermal bridging could add 50% to basic calculated heat losses and incidental gains might raise the background temp of their house to 11 degrees.

 

17 minutes ago, JSHarris said:

It's pretty damned clear that there's more than a 2:1 range for a 2013 house, so what do you think the range would be for a 1975 house?

 

 

Your general argument that every house can be different constitutes a mockery of science. How would you regard an NHS consultant in respiratory medicine who said "everyone has unique DNA therefore I am going to ignore the evidence that smoking shortens lives".

[Lesgrandepotato]

32 minutes ago, billt said:

 

Actually that looks pretty good to me, well into the realm of diminishing returns. A typical 1970s house would have 50mm of loft insulation, no wall insulation and single glazed windows. Presumably the cavities are insulated as well as the 60mm of celotex.

 

Your 1100l of oil sounds quite credible, bearing in mind that you keep the room temperatures low (a lot of people seem to like 23C+) and last winter was very mild. You might find your consumption increases significantly in a cold winter.

We haven’t done the cavities. Chronic fear of damp ingress given our damp Cumbrian location! 

[Jeremy Harris]

32 minutes ago, epsilonGreedy said:

 

You don't have to do anything but why do you feel entitled to mock a book that attempts to produce a more accurate model?

 

One of the most common sources of selfbuild dissatisfaction is from people who end up with thermally dysfunctional houses. Some end up buying electric panel radiators and others suffer sleepless nights in over heating properties. Selfbuilders will surely benefit from reading a book that highlights that thermal bridging could add 50% to basic calculated heat losses and incidental gains might raise the background temp of their house to 11 degrees.

 

 

Your general argument that every house can be different constitutes a mockery of science. How would you regard an NHS consultant in respiratory medicine who said "everyone has unique DNA therefore I am going to ignore the evidence that smoking shortens lives".

 

 

Please READ what I've written, then point out exactly where I've "mocked" anything.please.  All I've done is state the obvious, that there is a very wide variation between the best and worst house thermal performance in any particular period, so any attempt to determine to one decimal place any relative performance attribute is flawed.  If you can produce hard, independent, evidence to show that there is not a wide performance variation between houses built in any particular period, then I'd be more than happy to read it.

 

If you don't believe that every house can be different, then just take a look at EPC bands for existing housing stock.  The EPC for existing houses is a pretty crude tool, but even that shows variations of greater than 2:1 in thermal performance between seemingly similar houses.

 

if that's not good enough for you, then go around and ask people how much they spend on heating, and see how wide a variation there is in reality.  Even this thread has highlighted differences, with you taking the view that the OP's energy use is low and others taking the view that it's about right.

[jack]

Guys, can we please tone it down a notch? 

 

[epsilonGreedy]

16 minutes ago, JSHarris said:

Please READ what I've written, then point out exactly where I've "mocked" anything.please.  All I've done is state the obvious, that there is a very wide variation between the best and worst house thermal performance in any particular period

 

 

And equally I have made a reasonable claim that there has been a 2.7 thermal improvement factor in houses built between 1975 and 2013. From that general fact I inferred there was something strange with the annual heating calculation posted by the OP. When the OP started this thread the HBB was open at the table showing annual heating of 3 generations of houses and I noted the OPs figures were strange for an improved 1970s house, ballpark maths in my head placed the OP's house half way from 2013 standards to Passiv performance levels.

 

If I was debating with someone with less knowledge than yourself I would have posted using longer more qualified and less ambiguous sentences, I assumed incorrectly you would understand that 2.7 referred to averages across millions of houses, not every individual house built in the UK.

[Dreadnaught]

At the annual BuildHub summer party, I vote for these two to be the two captains for the tug-of-war 

[jack]

27 minutes ago, epsilonGreedy said:

And equally I have made a reasonable claim that there has been a 2.7 thermal improvement factor in houses built between 1975 and 2013. From that general fact I inferred there was something strange with the annual heating calculation posted by the OP. When the OP started this thread the HBB was open at the table showing annual heating of 3 generations of houses and I noted the OPs figures were strange for an improved 1970s house, ballpark maths in my head placed the OP's house half way from 2013 standards to Passiv performance levels.

 

If I was debating with someone with less knowledge than yourself I would have posted using longer more qualified and less ambiguous sentences, I assumed incorrectly you would understand that 2.7 referred to averages across millions of houses, not every individual house built in the UK.

 

But I asked nicely! 

 

[joe90]

Just to stick my oar in, even the same house in a different location will give a different result, Jeremy’s house is in a sheltered location facing the sun, we are on a windswept flat location near the Atlantic but still facing the sun ☀️