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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    • CommentAuthorJonG
    • CommentTimeSep 14th 2015
    We install a lot of Intergas boilers which is effectively 4 boilers in 1. Multi point hot water heater, combi, system, OV. The multipoint can work on its own and requires no pump just cold in and power.

    If you use E7 bear in mind that an ASHP of any variant will usually run during the day when you pay the higher rate, our customers who have experimented with it went back to normal rate, plus COP drops on the HP due to low air temps at night.

    Modern defrost strategy is fairly complex and monitors coil temp, gas temps, water temp etc. before deciding a defrost is required, there are then min run times before the next episode on some units. It is all naturally unit specific. Also an A2W has the energy from a buffer or heating system to effect a quick defrost, not sure if it is quicker than an A2A but the eventual SCOP would reflect the defrost on both.

    Standing losses are a moot point, if the energy goes into an airing cupboard and avoids the need for a tumble drier happy days, or offsets space heating in winter. Additional insulation around the cylinder and its enclosure will create a stasis eventually where thermal losses slow down or stop due to the lack of a gradient between the surface temp of the tank and the air temp in the enclosure.

    Cylinder proximity, pipe size, material, insulation, locality etc. can all be influenced to improve standing losses.
    • CommentTimeSep 15th 2015
    What's OV?
    Open vented?

    • CommentAuthormike7
    • CommentTimeSep 28th 2015
    Sep 3rd 2015
    quote :-

    'Posted By: mike7
    "You'd expect the SCOP of a DHW heat pump to be higher than for one doing space heating as it would spend a bigger proportion of its time in mild COP-friendly temperatures".

    My brain hurts. What does that mean. The delta T for DHW is a lot greater than that for space heating, so how come a greater COP?'

    Sorry djh - what I should have said is:- 'In MY situation where I'm space heating most of the time with air from my aircon emitter at no more than 45C I'd be happy to get DHW to 45C, and THEN I'd expect the SCOP to be higher......'

    ( I'm using the existing lpg boiler, rads and immersion to top up when needed.)

    There's also the point that if you can arrange to heat incoming mains water - typically at 10C - incrementally, perhaps in two passes, one from 10C to 30C and the second from 30C to 45C then the COP for the 1st pass should be high.
    Posted By: djh on a different thread
    Posted By: WillInAberdeena high-efficiency (>100%) gas/lpg water heater is used for hot water.

    You know we're going to end up disagreeing, but I'll bite anyway. Link for > 100% efficient gas water heater please?

    Thought you'd like that one :-))

    For example: "up to 107% net thermal efficiency."
    Other brands are available..

    It's all down to the flue temperature. The Net Calorific Value of the gas is defined as: the energy available when the gas is burned and the products are cooled to 15degC without any condensation. However a water heater is exchanging heat with cold mains water which comes at 10ish degC. So the flue can be really cooled, lots of condensation, lots more energy can be recovered, more than 100% of the Net calorific value. Unlike a CH boiler which is condensing again a warmish CH circuit so will have a warmer flue and less condensation.

    Makes great sales pitch, but more seriously it is a more efficient way to use gas than to burn it in a 50% efficient power station, with transmission and standing losses on top before you get hot water out the tap.
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