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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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  1.  
    Hi,

    Maybe a bit of an obscure question, We have a new one of the above. The installers have advised us that all the thermostatic radiator valves must be fully open all the time so the unit can work at highest efficiency, and so that the compressor lasts longer.

    Things become uncomfortable in many rooms, especially at night when one wishes a cooler temperature in the bedrooms. Plus, this advice seems to somewhat defeat the point of having thermostatic radiator valves.

    Our house has no inner room thermostats, rather one outer thermostat situated under the eaves of a west-facing wall - this is a common set-up here in Sweden.

    Does anyone know if the installer's advice is correct? The Bosch manual says that we can turn down thermostatic valves as we wish, so we're awfully confused.

    Thanks
    •  
      CommentAuthordjh
    • CommentTimeApr 2nd 2018
     
    All the information I can see via a search is in Swedish, so I can't help. Have you asked the installer about what the Bosch manual says? Have you asked Bosch about whatever the installer says?
    • CommentAuthorgoodevans
    • CommentTimeApr 3rd 2018
     
    As DJH said all the instructions I can find are in foreign. So we are guessing here.

    Is the unit really an mvhr - the only diagram I can find suggests that it draws fresh air in from outside via trickle vents. https://www.bosch-climate.se/produkter/franluftsvarme/compress-4000-ew/oversikt/ I think it is more properly called a MEV unit

    It looks like this has a heat pump so...

    Rule 1 - the lower the temperature of the water output the more efficient the unit will be.

    so I would use the TRV's to auto-balance the system and keep the desired temp in each room but turn down the temperature of the radiator water on the unit to as low as possible but still allow all the rooms to get to temperature. In mid winter/cold snaps the radiator water temperature needs to be higher than Autumn/Spring.

    counterintuitvly - the longer the unit operates as a heat pump each day the more efficient it is - If the radiators are luke warm with the TRV's open all day that is ideal.

    This assumes the radiator water temperature can be set to a different temp to the DHW temperature.
  2.  
    Thanks for your comments - I'm trying to get hold of Bosch :)

    Yes, it draws air in through trickle vents, although the unit also recycles the heat from the exhaust vents. Our old one was Nibe Fighter 310 (English manual here: http://www.nibeonline.com/pdf/511350-4.pdf). It has a compressor, a condenser, a supplemental electric heater, and a pump. It uses a combination of the outdoor temperature and a "heat curve" which is specific to mid-west Sweden, to determine the its water temperature. The electric heater unit supplements the compressor during cold weather (and after we've showered, I think).

    The water temperature is usually around 38 degrees, sometimes creeping up to 46, occasionally 56 for very short bursts.

    It also cycles between hot water and radiator every 35 minutes.

    So, goodevans, your comment "If the radiators are luke warm with the TRV's open all day that is ideal." matches the installer's advice, and is generally what we experience in most rooms during the day. This gives a nice 21-22 degrees. Problems come when the sun hits the four east facing rooms during the day, when we cook and in the evening when wanting to sleep. This is where I was thinking TRVs would help. I guess we'll have to choose between efficiency and comfort :)

    I'll check if we can have different temperatures for radiators and DHW
    • CommentAuthorgoodevans
    • CommentTimeApr 4th 2018
     
    It is not efficient to heat a house warmer than is required under most circumstances and certainly not to the point beyond comfortable. So I would use the TRV's to shutdown/slowdown the heating or install an override thermostat to turn off the central heating entirely if a room gets above 'warm'. (wireless thermostats/relay pairs can be bought to allow the thermostat to be located away from the heat pump without re-wireing the house.
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