C&G 6084 (Energy efficiency).

[Ed Sirett]

I thought one or two of you might be interested to know how I got on with the 'Energy Efficiency Course'. (mandatory exam pass before 31/3/6 required to remain CORGI registered).

We had considerable discussion about several contentious issues.

1) The boiler sizing method makes no allowance for the draughtiness of the home and will come up with (IMHO) too small a boiler if the assessment procedures are used without thought.

2) Currently there is a massive culture of continuing to fit non-condensing units claiming an exception where non are allowed. Since the replacement of boilers is now notifiable this leads to a problem. However on the CORGI web site for notifying the work (self certified as complying) there are exemption codes to allow you to specify that a regular boiler is compliant. Make of that what you sill.

3) Now this will please you know who - not. We (That is at least three of the students) argued with the tutor when he started to tell us that a 45litre super-fast [1] recovery cylinder could provide continuous hot water enough to supply a 4 bar ST power shower. The guy next to me said he'd just taken one out because it did not work. The tutor said that he often had a fights almost break out over this subject. The arguments became quite heated and caused the boss to come in to reinforce the 'staff' who then made a you-know-who style declaration from the sales brochure.

He said half a ton of water at 26.5 litre minute when connected to a 30kW boiler with 35C rise. The cylinder initially at 60C. I carefully wrote down his claim and then come lunch time did calculations showed that this was plainly impossible. I sort of guessed it was over the top but the calculations showed it was not even close.

Afterwards he confided that whilst he agreed with my calculations he wanted to get people thinking about the need to store less HW (with its storage losses). I pointed out that the merits of fast recovery cylinders don't need sales spin...

[1] 1" connection divides into a multiple-10mm microbore indirect coils each of about 6 turns.

[Mike]

Oh dear.

Storage losses on a highly insulated tank (Albion Mainsflow for example) are low. And in any case most/all of the loss is to the house so you just don't use the CH quite so much to make up. I would have thought having a boiler frantically trying to modulate itself to one's use of the shower would be far more inefficient.

[John Stumbles]

The method makes a number of other simplifying assumptions e.g. no allowance for types of floor, and just adding the rad output for extensions, which also seem quite wrong. We raised these issues and were told that they'd been simplified out because they made little enough difference to the requirement of the whole house that it didn't matter: our lecturer said he'd been sceptical at first but had checked the figures against traditional methods and convinced himself.

Looking at the figures for a house I did recently the vent loss was about

1/6th of the fabric loss, so this also seems a reasonable simplification. I suppose a house would have to be pathologically draughty (like no glass in the windows!) to seriously skew the figures.

I thought there were only exemptions for contracts (ahem!) "agreed" before

1/4/5 (which have to be completed by 1/7/5) and replacement under warranty. Something like 7777 and 8888.

BTW where did you do yours?

[Doctor Evil]

It could be close if the temperature on the inlet water is very high.

Ballpark is that 30kW will deliver about 12-13 l/m of instant hot water @

35C temp rise. If there is 45 litres of hot water stored at 60C and the coil takes all of the boilers output, then to be infinitely continuous, the shower must be not more than 13 l/min. Anything over this and the hot water in the cylinder will gradually deplete. It will fill an average bath OK, then run out of hot water. Depending on how the coil is arranged inside the cylinder, it could drop back to about 12 l/min and never run cold.

They do. Few people use them. One old hand on a plumbers merchants counter I know had never even heard of them.

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[Ian Stirling]

Not to mention that a roll of loft insulation wrapped round the tank seriously helps the numbers too.

[Tony Bryer]

On the model detached house we use to check our SuperHeat program the ventilation rate used in the SAP worksheet is 0.81 ach and the ventilation heat loss (fabric to current BR standards) is 38% of the total. Obviously as you make the fabric standards tighter and tighter the ventilation loss as a proportion of the whole tends to increase, which is why there is now a lot more emphasis on 'build tight, ventilate right' and possible compulsory pressure testing of new dwellings.

[Ed Sirett]

1st Training (Nr. Huntingdon).