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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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  1.  
    Looking to upgrade radiators in bedrooms, currently single rads in every room.

    We will eventually run an ASHP - should we be engineering out the radiators and upgrading the insulation/windows instead? (More costly)

    Should we be looking at hydronic plinth heaters instead? Just upgrade to Type 22 radiators the largest we can fit in each room? Maybe look at air to air heating on the landing only?

    Spreader plates across joists?

    Maybe electric heating instead?

    Aesthetically we aren't looking for anything fancy

    Ideas appreciated
    • CommentAuthortony
    • CommentTimeJul 8th 2024
     
    I would try switching them off, might be ok without them. If not the add insulation and 3g not forgetting to do the draughtproofing
  2.  
    How would I know at this point if they are not needed? I can disconnect them all but no way to check if ground floor radiators are sufficient to heat upstairs also particularly at lower temps... And we're in summer (apparently)
  3.  
    My thoughts would be:

    - you will need heating on the first floor almost certainly, especially as you prob won't take the insulation levels and air tighness levels to a point to negate heating.
    - you've alerady got a CH system, so unless you particularly WANT UFH, then make use of what's there (pipework wise) assuming it's 15mm and not mini or micro bore. Will need a flush through.
    - you could take a risk and cap the existing pipework in the wall/below floor, for a future rad installation in each room, and have a decent sized rad in the landing, but unless you keep bedroom doors open, the rooms will get cold. If you've anyone siting in the bedrooms, studying/reading/on computers, they will be uncomfortable at less than 19/20oC, which is warmer than normal sleeping temps of say 17oC, so you'll need to cater for that.
    - I personally think UFH on upper floors is often overkill (carpets/beds/wardrobes covering floor), and a lot of work, but it's not wrong. Often people want a quick burst of heat just before they wake up, not constant heat all day, so UFH isn't ideal for that scenario. Ditto, quick heat before bedtime (studying time) but not so warm for sleeping.
    - determine how you're going to insulate (what's possible/not detrimentalto the fabric/but to a decent level), and therefore you can calc the heatloss per room. Not difficult.
    - size the rads for say 20oC delta T (say 40oC water off ASHP)
    - hopefully with the reduced heatloss thru insualtion, draft proofing etc, you won't need much bigger rads than existing, but caluclate it, don't guess.
    - you won't get a consistent answer on GBF about 2G versus 3G, because there are various good arguements for both, which likely means you won't be wrong doing either. I like 3G, but 2G is good too, and often provide that for clients. There is a lot of heat loss thru windows at Uval of 1.2, versus walls of say 0.17, so windows in gerenal are weak points, but making the energy saving case versus cost to buy 3G is not easy. It's a comfort thing for me, but then the grid is getting greener, and your consumption less with an ASHP, so pick one and go with it. How the window is fitted prob will have a bigger impact.
    - I would go for simple approaches to heating, insulation, draught proofing, and do it well, as you'll run out of cash/enthusiasm/patience if you try to be to idealistic. It's somewhere to have time to live, not a scientific experiment :bigsmile:
  4.  
    Wise words from GreenPaddy.
    Made me think about my own perfectionism, which perversely stops me getting on with a lot of things.
  5.  
    Thankyou GP for your detailed response.

    It's a difficult one, as the floor has to come to to up anyway for the rewire, the copper is 15mm to each rear but I'm thinking while I'm in there just to replace it all with new. I've dealt with far too many leaks through work where old pipework leaks.

    So may as well upgrade heating elements. What's the best website for heatloss calculations?
    •  
      CommentAuthordjh
    • CommentTimeJul 9th 2024
     
    Posted By: VictorianecoSo may as well upgrade heating elements.
    Upgrade the insulation and airtightness before upgrading heating elements. You'll likely need smaller radiators after improving the fabric, but will need the existing ones until the work is done.
  6.  
    https://www.heatgeek.com/how-to-size-my-heat-pump-or-boiler-heat-loss-cheat-sheet/

    Use the cheat sheet here to guesstimate the heat loss per room

    Multiply that by 3 to get the radiator sizes (because you will be running at much lower temperature than they are rated at)

    Much more good stuff on his website and YouTube channel.

    Radiators are remarkably cheap now, especially if you round up to the standard 900 1200 or 1800mm K2 sizes, so lean towards oversizing them.
    • CommentAuthorGreenPaddy
    • CommentTimeJul 10th 2024
     
    I use my own calcs on excel, based to some extent on SAP.
    Essentially measure the surface areas for all the rooms, multiply those by the Uvalues for the elements of each room, to give the surface losses. Then add in the allowances for cold bridging, and also for ventilation losses. That gives losses per room, and of course a total for the house, to arrive at a heat source size. I add on a nominal 20% to the rad sizing, as you need to be able to increase room temp, not just maintain it.

    It's all basic maths, but I use excel to do it faster, and repeatably, and see quickly what different insulation build-ups will deliver. It's worked ok for the last 15 years.

    Sizing rads - be careful about the power output stated on the rads' in the internet shops. They may be shown at delta T of 50, or even 70. The relationship between delta T and power out is NOT linear, so halving the delta T you will need to MORE than double the rad size.
    •  
      CommentAuthorfostertom
    • CommentTimeJul 11th 2024 edited
     
    Posted By: GreenPaddyI add on a nominal 20% to the rad sizing, as you need to be able to increase room temp, not just maintain it.
    That doesn't necessarily require oversizing. When room temp is lower than desired/design temp, the delta-t (temp difference between rad water and room air) will be greater therefore heat output in surplus, proportionately, declining to normal as air temp rises. Not by a lot, admittedly, with trad 60o flow temp, but becomes a more significant surplus with large rads/lower design flow temp, till with UFH the surplus is so effective that room stat/TRV is not necessary.
  7.  
    Will I have looked at the heatgeek website which has some good information

    As my home is a 1960s build that will have the cavity installed and then will look to get EWI along with double or maybe triple glazing which figure would you use?

    I was thinking of basing everything at 40w per M2 being mid range between 30 and 50

    Any thoughts?
  8.  
    going for a flat rate / m2 doesn't do a very good job. Too many variables to upset the flat rate.
    The amount of external wall area vs. the floor area
    The window area (and type)
    Floor and / or ceiling thermal values
    Designed flow rate and flow temp.

    All of the above will conspire to invalidate a flat rate sizing attempt. (and probably more that I have forgotten)

    There are lots of calculators around and it doesn't take long to do the job properly i.e. room by room calculations
  9.  
    Just using the EST spreadsheet and it doesn't give a good option of U-values

    It also appears to have a blanket 400w for thermal bridging (I guess this should be per overall property not per room) - possibly aimed at whole house heat sizing...

    Do you have a recommended link for room? and do you include walls and floors that are next to other heated rooms? As i suppose they're not really a loss but could be deemed as a gain for calculation?
    • CommentAuthorphiledge
    • CommentTimeAug 26th 2024
     
    If there's a gain for one room, there'll be the exact same loss for the other room. If you're using excel it's easy to do a calc for each wall of each room
  10.  
    Yes, so in that scenario, are we not calculating losses from internal walls?
  11.  
    Correct, you don't normally calculate internal walls. Calculations assume the house is kept at the same temp. throughout so there will be no loss or gain through internal walls since each side is at the same temp. so no heat transfer.
    • CommentAuthorphiledge
    • CommentTimeAug 27th 2024
     
    If you're calculating whole house heat loss then no need to consider internal walls. If your sizing rads per room then internal walls need to be considered, IMO.

    If you've got a bathroom with a target temp of 21C surrounded by bedrooms and landing with a target temp of 18C then you'll undersized the bathroom rad and oversize the bedroom/landing rads if you don't consider internal losses/gains. If you're adding a blanket % increase in rad size then it's not likely to make much difference, but it's very easy to do in excel so likely worthwhile
  12.  
    The heat transmission through internal walls in our MCS room-by-room calcs was 10s of Watts, negligible compared to the 100s of Watts of transmission by air flow from one room to another. The different air change rates used for each room, were entirely made up by MCS as nobody has room-by-room air leakage test data.

    So in other words, don't sweat the details, this exercise is all a big guestimate anyway.

    On the plus side, Screwfix sell their 2kW radiators for only £11 more than their 1.4kW radiators. So don't worry just buy the biggest radiator that fits the space and you can run them much cooler and still get hundreds of Watts out of them.
    • CommentAuthorphiledge
    • CommentTimeAug 27th 2024
     
    Just a look at our calculations from a couple of decades ago and internal walls in our family bathroom account for 104 Watts out of a total of 358 for the room, so just under a third of room losses down to internal walls.
  13.  
    Interesting, looking back at our MCS calc for the bathroom (6m2 floor) they said

    45W through internal walls (8% of total)
    107W through external walls and windows
    385W due to 3ACH ventilation with external air at -4deg

    Total radiator 537 W


    But it seems to me that most of the ventilation that is extracted from the bathroom, is 18deg air that is sucked into the bathroom from other rooms (door is undercut). So much of the 385W ventilation heat should come from the other rooms' radiators, not the bathroom's. The bathroom radiator just tops it up to 21deg.

    So bathroom radiator load should be nearer 200W and other rooms should be increased accordingly.


    We have at least a 1kW radiator in every room, so don't worry about it at all :-)
    •  
      CommentAuthordjh
    • CommentTimeAug 29th 2024 edited
     
    What do the various calculations of internal wall transmission assume about the construction? Maybe older calculations assume timber studs with plasterboard whilst more modern calculations assume the presence of sound insulation as well? I can't remember when building regs changed.
  14.  
    I have been doing some basic calcs and most rooms range between 300w and 1000w, by using type 21 rads we can pretty much achieve all the figures easily without the added bulk of type 22 rads.

    All my calcs have been based on 80mm cavity insulation, 100mm EPS on external (u value 0.17), window u values of 1.4 and ventilation based on 0.22 air changes an hour.

    I've even upsized the radiators in width, often finding 1000mm radiators are cheaper than the 600 required in some rooms.

    This gives myself some wiggle room as the aim is to probably go for 200mm EPS and hopefully have better windows dependent on price of course
    •  
      CommentAuthordjh
    • CommentTimeOct 2nd 2024
     
    Posted By: Victorianecoventilation based on 0.22 air changes an hour.
    That sounds a bit low.
  15.  
    What figure would you use then? That was from a calculator that says if using a mvhr unit that is 66% efficient

    I see no point in having arbitrary numbers for rooms? Surely we'd want to look at whole house ventilation rate divided by room volumes?
  16.  
    Posted By: djhThat sounds a bit low.



    Posted By: VictorianecoI see no point in having arbitrary numbers for rooms? Surely we'd want to look at whole house ventilation rate divided by room volumes?


    I'll let @djh expand on their point, but suspect this is reference to passivhaus practice where you do tailor the ventilation rates to specific rooms because you want to extract from moisture sources (kitchen hob, showers) and provide fresh air to sleeping and living areas. Interstitial spaces like lobbies are then ventilated by the through-flow of air, rather than receiving dedicated input/extract.

    This means you aren't over-ventilating the whole house at worst case figures. Passipedia reckons that this equates to ventilation rates of around 0.3-04 air changes per hour.

    I should also point out that in passivhaus MVHR, the ventilation rate is actually tailored to the number of occupants (30 m³/h per person), rather than the room volumes (which are assumed at 2.5m standard height for the purposes of the calculation). The justification for this is that in residential accommodation, the amount of emissions to be extracted from the building does not generally change with increased room height.
  17.  
    So if you're ventilating 30m3 an hour and there's 4 people that's 120m3

    Imagine a 10m x 10m home, 5m high that's 500m3

    500/120 = 0.24 air changes an hour

    Obviously volume goes up or down, so too does number of occupants. So an air change rate is variable and using 1.0 or so is not realistic...

    Throw in heat recovery etc. The air change amount is even less
    •  
      CommentAuthordjh
    • CommentTimeOct 4th 2024
     
    Actually I was thinking about building regs. "A minimum rate of 0.3 litres per second per m² of internal floor area". So for a 2-storey 10 m x 10 m house that's 200 * 0.3 = 60 l/s or 216 m³/hr. With a volume of 500 m³ that's an ACH of 0.432 That's why I said 0.22 was low. It doesn't meet building regs by a considerable margin.

    PH says 20 m³/hr per person and a minimum of 0.3 ACH. They recommend ventilation systems are 30% oversized. See https://passiv.de/downloads/03_building_criteria_en.pdf
  18.  
    Would it matter if the house isn't PH though? Then where do the guides come in? I guess if I just spec it on CIBSE guides it will just means rads are oversized

    Going back to my original thought process of type 21 rads in every room, will be more than sufficient
    •  
      CommentAuthordjh
    • CommentTimeOct 5th 2024
     
    You have to follow the building regs and the simplest way is to follow the AD. The PH stuff is just guidance as far as you are concerned. Don't know what guides you mean.
  19.  
    I've got my radiator sizes performed by the MCS accreditted heat pump installer. Only slightly bigger than what I calculated but more to do with air exchange rates

    There are two rooms we are going to struggle for space on the walls. What are people's best choices for this situation? Fans?

    Room is ground floor with suspended timber floor
   
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