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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.

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    • CommentAuthorjamesingram
    • CommentTimeMar 12th 2018 edited
    So a challenge for the forum.
    I've a friend whos looking for the best solution for HWS , with the restrictions on any external changes the choices are very limited (no PV, ASHP, Solar thermal)
    Space heating the goal would be insulation, the idea of E7 thermal store came to mind , but seems better to invest in insulation, airtightness etc, (lets leave that for now)
    for HW my first thoughts would be a main pressure cylinder with 2 immersions high Standard/low E7, which is the obvious standard solution.
    anyone got some better ideas
    here's the brief

    Hot water design

    Aim: Adequate cost-effective hot water provision to suit house being enlarged from 3-5 bed.

    Current design is:
    • All electric (no other fuel to property)
    • “Economy 7” dual tariff meters
    • HW cylinder is 1500 x 450 Economy 7 vented
    • House heating supplied by two storage radiators (not sufficient!!)
    • Bathroom shower is currently “Aqualisa Quartz Smart – gravity pumped” – good.
    • Shower room shower is unknown (hidden behind tiles and not working properly).

    Factors to consider:
    • No change to external appearance of house permitted (alternative heating sources not practicable).
    • New house heating will be provided by electric under-floor (to ground floor) and by electric skirting radiators (first and second floors).
    o Hot water provision will be independent from house heating
    o House heating will be mostly in use outside “Economy 7” hours.
    • Expected use of house is single person, part-time (typically one cloths wash, one dish wash, five showers per week). However want to have solution that will adequately cope with typical household of four people (for when guests visit or for when house is sold).
    o Want capacity for at least three “good power” showers in the morning (current tank can provide for two only). Bath infrequently used.

    Layman’s thoughts:
    • Will need to move hot water tank anyway
    o Option to change to more efficient type of system?
    • Ideal solution will probably have limited or nil hot water storage capacity (to minimise unnecessary heating)
    • When second floor is added, showers on first floor will not need to b
    • CommentAuthortony
    • CommentTimeMar 12th 2018
    Heat pump for me, underfloor electric heating will be well expensive better to fit a wet system and decide on how to power it as things change. For now a heat pump will be 350 to 450% efficient, whereas direct electric will only be 100%

    Hot water heat pump too. Ground source could work visually, as nothing outside.
    • CommentAuthorowlman
    • CommentTimeMar 12th 2018
    What is the electricity supply, single or 3 phase?
    • CommentAuthorowlman
    • CommentTimeMar 12th 2018
    How about point of use instantaneous hot water.
    Owlman single phase , instantaneous would be good but i was under the impression they'd need 3 phase to get a decent system
    Tony , unfortunately HP is out , its on a marina type developement next to the river, no grounds.
    ASHP is out as nowhere to site it (cold loft with adequate ventilation ? pretty sure thats out as it'll pull heat out the house over time).
    Now it does have a jetty , so the idea of water/water HP popped up but I'm not sure the freehold/estate mgmt or the environment agency would want a coil in their river/mooring area and im guessing (if like GSHP) it would need to be sizable so probably practially speaking also out.
    • CommentAuthorCWatters
    • CommentTimeMar 12th 2018
    Posted By: jamesingram
    • New house heating will be provided by electric under-floor (to ground floor)

    Will the occupier(s) be at work during the daytime? If so then I think UFH might be a mistake.

    Is there enough insulation in the floor or headroom to add more?
    • CommentAuthortony
    • CommentTimeMar 12th 2018
    Water source heat pump leaps into pole position
    Bottled propane 'multipoint' instant heater - Rinnai or similar. Cheaper and greener than electric. Less capital cost than a pressurised cylinder.
    • CommentAuthorgoodevans
    • CommentTimeMar 12th 2018
    Rather than a coil in the water - can you pump out the water, steal the heat and put it back again after :bigsmile:
    • CommentAuthorDarylP
    • CommentTimeMar 12th 2018
    I am with Will above, Rinnai on LPG bottles...... :bigsmile:
    Long term I wouldn't make any assumptions about Economy 7, with the rollout of smart meters its likely to disappear in favour of a more dynamic time of day pricing system, which may or may not to be your advantage depending on how much thermal storage you have built into your design and how you can use this thermal storage.

    I would second WSHP, but because its unusual technology might end up being expensive. It doesn't need to be sizeable as water has ~2000 times the heat capacity of air, so you don't need too much of it. For example if your heat pump reduces the marina water by for example 5C, and you are heating a 200l tank by 40 degrees, you only need (40/5)* 200l of marina water i.e. 8 m3 which is nothing. You should also check whether WSHP is covered by RHI, if it is as per GSHP then it would provide a good source of funding; you may need to phone OFGEM to ask?

    Also, factor in, a marina might have milder weather than predicted by SAP because of the presence of the water nearby, so less heat demand?
    basic Maths error, 8 m3 should be 1.6 m3 in my post above, so even less....
    • CommentTimeMar 13th 2018
    Posted By: jamesingramHW cylinder is 1500 x 450 Economy 7 vented
    What is wrong with this.
    The losses can be a bit high, but that is easy to overcome.
    What I have. Works fine and I can always turn the storage temperature up from 50°C to 65°C to get more storage if needed. It has coped with 4 adults in the house in the past.
    To be honest, if it is just one person and just a shower, a 100lt cylinder would do the job. So maybe fit a smaller cylinder for now, and add one if the household use gets expanded.

    Very easy to try and reinvent the wheel for no real benefit.

    A water source heat pump would be fun to fit, but getting a licence may be difficult, as would the piping. The maintenance costs could also be high, filters would need changing often. An air source heat pump may need planning permission. But those options are not viable anyway.

    Really comes down to whether you want to fit a vented system with no G3 certification, or an unvented system with G3 certification and an annual safety check.
    Or a Sunamp.

    My shower has a flow of around 10 lt/minute (cheapest and smallest pump from Screwfix over a decade ago).
    To get a similar direct heating shower you would need about a 21 kW one.
    Added the Mira showers power/flow chart for you.
      Mira shower.jpg
    • CommentTimeMar 13th 2018
    And just for some secondary information, I have just ordered a replacement 200lt cylinder for £252.
    Quick look for an E7 indirect unvented cylinder and the price is £525, so over double the price.
    • CommentTimeMar 13th 2018 edited
    Re the space heating.
    A combination of more modern storage heaters and Air to Air heat pumps, if you can find somewhere to hide the collector (modify loft maybe).

    Or you could heat a large cylinder of water and pump it though whatever you want i.e. UFH, radiators, fan assisted radiators, skirting, forced air duct heating.

    With WSHPs you don't put a coil in the water, that would be silly, you pump the water though a plate heat exchanger.
    • CommentAuthorTimSmall
    • CommentTimeMar 13th 2018
    Water source heat pump sounds the best option. Urban rivers usually suffer from heat pollution, so extracting a bit of heat from it will be doing them a favour.

    You can either bury a loop in the water bank or bed, or extract water, put it through a heat exchanger and then put it back. The former is simpler if you can get permission.

    You then have the option of a thermal store (doesn't need a legionella cycle), or high pressure cylinder (which does, but you can time that to run on E7).

    With the thermal store, you can either run it a high temperatures, or at a lowish temperature (e.g. 40) and use on-demand top-up for DHW if necessary (e.g. a 9 kW "amptec")?

    Another alternative is E7 direct heating with a thermal store, but you need good controls to get the thermal store "charge" right (so that you don't overheat or underheat it).
    Water in a port or marina likely has too much 'stuff' floating in it to go through a heat exchanger. You'd want to bury a loop in the sea bed and pump clean water through it. But:

    Cost savings on daily dhw usage for one person is not going to justify any of these fancy or experimental hookups.
    • CommentAuthortony
    • CommentTimeMar 13th 2018
    But on the heating they will assuming a none too well insulated building
    • CommentAuthorfinnian
    • CommentTimeMar 13th 2018 edited
    There are air source heat pumps (integrated with a hot water cylinder) without an external unit: ducting is used for supply/return air.

    Although any potential energy saving is going to be pretty small compared to heating the house efficiently. Actually you can also get ducted external split-system ASHP units (i.e, the 'external' unit sits in the loft with ducts in/out for the external air) but this starts to be a bit unusual.
    We have a similar dilemma (albeit with PV) and have opted for a SunAmp thermal store.

    They reckon a 3kWh unit is equivalent to 90-138 litres storage which should be more than enough for a single occupant and have potential for a couple more showers in reserve.

    I don't know much about E7 but if I understand it correctly you could 'fill up' overnight at times of low demand and then have a decent amount stored overnight.

    The newer units have 'dual ports' which means they can feed DHW and Space Heating if this was an option (although that might mean a larger 6kW unit is required).

    Not cheap (or renewable in this setup - until the grid is decarbonised...) but the storage losses are ridiculously small and it's a modular system so can be added to later if required.

    Dimensions are about half a kitchen unit (580mm x 380mm), height varies with the kWh capacity.
    Thomas, did you get a ballpark price on that Sunamp 3kW unit
    finnian, any brands you could point me to , thanks
    LPG is out I think , nowhere to put the gas cylinder, I hear you re cost for fancy solution over £saved ,
    I need to investigate the RHI currently to see what thats offering, been a few years since I looked at it. anyone got an idea of returns currently.

    air/air isnt something i thought of re heating , put I fitted a few a decade ago an they'e working well on another job(commercial property) could be lower cost solution to improve the COP and get away from direct resistance heating. its the issue with hiding the outdoor unit that made me discount any air HP unit intially.
    WSHP needs more investigation I think also but is a much 'bigger' overall solution with perhaps the need to link it with a thermal store which makes the cost go up and up.
    as you say perhaps the cheapest obvious solution is the solution

    thanks everyone for your thoughts keep them coming
    Last A/A HP I heard was pretty intrusive! Louder than I had thought. Louder than I'd want on a quiet evening!
    Posted By: jamesingramThomas, did you get a ballpark price on that Sunamp 3kW unit

    It's complicated as we are going for a pair of units but, splitting the cost straight in half suggests about £1750 all in.(obviously capital costs and install etc. will mean its probably not a straight split)...
    • CommentAuthortony
    • CommentTimeMar 13th 2018
    I don’t think you need a thermal store with a WSHP, just hot cylinder
    • CommentAuthorfinnian
    • CommentTimeMar 14th 2018
    The Ariston Nuos is the ASHP/cylinder that comes to mind.

    You would have to think about noise: even according to specs this is louder than a gas boiler. No doubt where and how it is installed (ducting and what kind of floor it is sitting on) would make a big difference. On the other hand it is only going to run an hour or two a day and you can program when it runs.
    • CommentAuthormike7
    • CommentTimeMar 14th 2018 edited
    <blockquote><cite>Posted By: jamesingram</cite> ASHP is out as nowhere to site it (cold loft with adequate ventilation ? pretty sure thats out as it'll pull heat out the house over time).
    Maybe more do-able than you'd think - even with no ducting to external at all. Depends on how big the attic is and whether the roof itself is a sufficiently good conductor, ie. uninsulated preferably,to keep the attic air temp from dropping lower than a degree or two below external.
    The Ariston Nuos for example consumes 700W average at a claimed COP of 3 or so, which means that the heat extraction from the loft air is 1400W. You could easily check what effect this would have on the air temp by putting a 1.5 kW fan heater in the attic for a few hours when the external temp is expected to be steady and measuring the temp rise.
    An advantage of it working without ventilation is that the air would become dehumidified so that there would be less chance of needing frequent defrost cycles during cold weather.
    I've got about the perfect situation for it here, so if I haven't persuaded you I think I've at least persuaded myself.
    • CommentAuthorringi
    • CommentTimeMar 18th 2018
    Posted By: SteamyTeaWith WSHPs you don't put a coil in the water, that would be silly, you pump the water though a plate heat exchanger.

    The reasons for often using a coil is that it removes the risk of the "river" water freezing and breaking the plate heat exchange. Also by using a coil, it can be 100% the same kit as is used for a ground source.
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