Has anyone any idea of how the Energy Efficiency rating of a house is arrived at, please?
(I'm as sceptical as anyone else re HIPs etc. so please no flood of posts re that. I simply wish to assess my own house so I can use that as a comparison figure when looking at house sale details.)
TIA
Brian
A man comes around to your house.
He looks at its basis construction and asks YOU if it has cavity wall insulation, loft insulations etc.....
If you don't know, he guesses
He fills this information into his little computer and out pops the answer in a from that looks similar to the things that you see stuck to fridges.
That's it
Oh, or it could be a woman.
tim
The commonest energy/emissions rating is the SAP (Standard Assessment Procedure) rating
You can download the SAP worksheet and try and do it by hand, but I warn you, you may lose the use of your higher reasoning faculties somewhere around the questions about heat loss coefficients and parameters.
Or there's always SBEM...
so in other words they pull a number out their arse and your stuck with it?
yes,
be prepared for some massive long calculations then. Or pay 200 notes and get someone to do it for you.
No, they do a lot of pretty involved calculations.
Their computer does a lot of involved calaculations based on numbers pulled out of their arse.
How many inspections does a HIP person do in a day? If it's more than 2 it can't be that reliable as it doesn't leave enough time for a decent inspection, questions and traveling assuming a normal 9-5 working day.
Its not that hard to do. I worked through all the heat loses, including the transfers between internal walls, when I fitted my CH 28 years ago. It only takes a few minutes to get the measurements, and a bit longer if you don't know how it was built to have a look. The calculations took about an hour without a computer.
The boiler sizing was the tricky one BTW.. all the books said you worked to an outside temp which was way too high (1C IIRC). I ignored it and worked to -10C. Just as well, we had that really cold spell when temperatures were down to -17C and below zero for ages. The neighbours all thought their heating was broken when it was still cold inside. 8-)
In message , The Natural Philosopher wrote
What is the entry level qualification in mathematics for the inspectors?
It cannot be any more difficult than the (simple) standard central heating calculations that are based on room dimensions, the construction of the walls/windows and a set of look up tables for the fiddle factors.
CH calculations used to be just as involved as HIP calculations. Then plumbers started to do CH and the maths had to be removed. Hence the tables of approximate radiator sizes for different room sizes. It works well enough if you go around and balance the system or fit TRVs or better controls.
HIPs are supposed to give you a more accurate energy rating so the maths is back but the computer does it for the inspector. I expect some basic addition and subtraction and the ability to spot gross errors is all that's needed.. (an old style O' level or a new A'level) probably ;-)
If you get a heating engineer in to design a medium-complex system he will probably still do the maths to size up all the bits BTW.
In message , "dennis@home" wrote
When I did my own CH it was more than just estimating radiator sizes based on a room size but the calculations were simple based on heat loss through single/double glazed windows, 9" brick or cavity wall construction, loft insulation etc. All the heat loss values came from standard look up tables as well as typical climatic conditions for my locality. Room sizes, pipes sizes and boiler sizes did come into the calculations but again basic multiplication and addition was all that was required.
For the average punter researching for this information may be the time consuming part of the process and he may think it worth while paying £200 to someone else to avoid the bother.
I assume the HIPs inspector is taking measurements and notes on the type of construction.
Doesn't the efficiency also relate to surrounding property. I live in a mid terrace property and for a period of around two years the property one side of me was virtually unheated (the owner living with relatives two house down the road). The property the other side of me was occupied by an elderly gentleman who used to 'live' in one room with a two bar electric fire. My heating bills went down by approximately 25% when new neighbours, with central heating, moved in.
Surely degree level mathematics these days?
An A at gcse maths would probably be enough but not all grade A at gcse. The range that pass at A is so large one student could be brilliant and another might not be able to shop alone.
There's a lot more to it - I sold my SAP Rating software in January, but spent many happy hours wrestling with the methodology.
Starting point is that fabric heat loss and ventilation loss, and the assumed demand for HW (based on floor area). SAP rating is a function of heating, DHW and lighting energy costs (not appliances)
The energy used for heating depends on the fabric and ventilation losses, less gains from hot water cylinder, hot water distribution, solar gains through windows (a function of orientation and glazing - low-E lets in less), gains for lighting (less if more low energy lamps), gain from CH pump where installed and assumed occupancy gains.
DHW usage is for HW, distribution and cylinder losses.
Lighting energy takes account of window size and orientation. With solar and lighting gains now being factored in, reducing window sizes is no longer an automatic route to Building Regs compliance - often doing so can make things worse.
Raw requirements are then adjusted to take account of controls and boiler efficiency and the net fuel required is multiplied by a notional energy cost. Energy cost/m2 is then turned into a SAP Rating.
The EPCs in HIPs also show an environmental rating which may not be the same as the SAP (which dates back to when fuel poverty, not global warming was the key driver) - e.g. bulk LPG is expensive, but clean.
Or cheat and copy next doors?
New builds aren't tested to make sure they meet the levels laid down in law and I saw something saying that very few of them would but as no one actually tests them no one cares.
Oh, but they are subject to inspection. The specs are laid down, and the BCO will make sure they are adhered to.
No, you can pay a different numpty to come up with another number and keep that instead
tim
>
The thing I read about was some test (can't remember what for) where they : - oh it's called the The Blower-Door Test
No, there are specialist firms that do it and a test is required on all new homes (or a sample on larger developments) built in England & Wales since 2006.
See
A key reason is that U-values have been forced down and down over the years and ventilation losses are now a significant proportion of the total. OK if it's wanted ventilation, not if not.
BRE tested a sample of new homes in 2005 (?) which had not been built with a view to being tested. Can't find a reference to it quickly but IIRC the test results ranged from 3 to 25: the first is very good, the second a place that leaks like a sieve and would be very hard to keep warm. Most new homes are designed to comply with a result of 7-8, but now that builders know that tests will be carried out my understanding is that 5-6 is now quite common. If it's a sample the BCO should only nominate the ones to be tested just before the test, so that there's no chance of putting the effort into those and ignoring the rest.
As an ex-BCO what pleases me about this test is that it 'sees' what the naked eye can't - missing flooring under baths or sinks and unfilled holes in odd places.
And now we have (almost) hermetically sealed house, how do we stop them going mouldy?
(I know the theoretical solution, I just wondered whether we use it)
tim
Which seem to be based on wild guesses (at least as far as HIP assessments are concerned). Three identical houses here have three different energy ratings.
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