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Green Building Bible, Fourth Edition
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    • CommentAuthorjohnuready
    • CommentTimeFeb 11th 2015
     
    Anybody monitoring their MVHR temperatures at the spigots in/out of the MVHR? I would like to checkout my results.

    I'm using a Vent Axia Kinetic.
    • CommentAuthorborpin
    • CommentTimeFeb 11th 2015
     
    My system reports them on the controller (Helios EC500). 5 Outside, 18 Inside, 16 Supply, 6 Exhaust. I do have the pre-heater running as it provides just enough extra heat.

    It is running slowly (3 out of 10) which helps the recovery.
    • CommentAuthorGreenfish
    • CommentTimeFeb 11th 2015
     
    John how are you measuring the temps, assuming you don't have a system like Borpin that reports them?

    Had a go using IR thermomter a little while ago, hoping this was wildly inaccurate as the results were so dissappointing. My other problem is that my wet/smelly extract rooms are not the hottest ones.
    • CommentAuthorborpin
    • CommentTimeFeb 11th 2015
     
    If you wanted to measure them you could use a EmonTH from the Open Energy Monitor folk. You need a base but the TH is battery powered and can connect quite a lot of DHT22 probes to it.
    • CommentAuthorjohnuready
    • CommentTimeFeb 12th 2015
     
    I'm using an online system to track loads of sensors I installed while building the bungalow.

    The first issue I have with my MVHR is the "From Atmosphere" temperature at the MVHR spigot. Its currently 3.7 C outside and I'm reading 8.1 C.

    The insulated pipe travels through a "cold" roof (vented) space anybody seen a temperature increase when insulated?

    Unfortunately I do not have sensor in the roof space, perhaps in the coming days.
    • CommentAuthorringi
    • CommentTimeFeb 12th 2015
     
    The outside air next to your dark colored building may be warmer then the outside reading you get.
    • CommentAuthorjohnuready
    • CommentTimeFeb 12th 2015 edited
     
    The bungalow is finished in yellow coloured lime render, outside sensor above ground at 2m's, air intake 3.5m's both on the east, 4m's apart.
    • CommentAuthorringi
    • CommentTimeFeb 12th 2015
     
    Did you confirm that both sensor read the same before installing them?

    Are the sensors digital? (If not the cable length to the A/D may effect the reading.)

    Is the outside sensor protected from rain and wind?
    • CommentAuthorjohnuready
    • CommentTimeFeb 12th 2015
     
    ringi -

    Good idea I have never bothered with confirming sensors before but in this case it's a good idea to check any variance. I have sensors in all 4 spigots.

    I am using DS18B20 1 Wire Digital with an accuracy of +/- 0.5 degree.

    Also loft space needs a sensor ASAP.

    Looks like I'm ordering new sensors.
    • CommentAuthorborpin
    • CommentTimeFeb 13th 2015
     
    Posted By: johnureadyI'm using an online system to track loads of sensors I installed while building the bungalow.
    Which one?
    • CommentAuthorjohnuready
    • CommentTimeFeb 15th 2015
     
    Anybody know the way to work out MVHR % efficiency if you know the 4 MVHR and outside temperatures?
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 15th 2015
     
    • CommentAuthorjohnuready
    • CommentTimeFeb 15th 2015
     
    Thanks Steamy but working on yesterdays numbers (unit now apart for cleaning) it was humid and the unit was running as 40%, calculates to 97% efficient but only 0.13kW, is that good?
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 15th 2015
     
    How much energy does the fan use?
    Hard to tell if it is good or not without knowing the mass of air that passed though the heat exchanger.
    • CommentAuthorjohnuready
    • CommentTimeFeb 15th 2015
     
    I'm running at 38 l/s with motors 150 W max
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 15th 2015 edited
     
    That will be 164 kg/hour of air and up to 0.15 kWh for the fan.

    For every 1°C difference the maximum energy is therefore 0.0456 kWh

    If your fan is running at 50% the power rating it is then using 0.075 kWh (or 75W continuous power).
    And if your heat exchanger is running at 95% efficiency then you can get 0.0433 kWh energy recovered
    You seem to be getting 3 times that, this implies that there was a larger temperature difference, 3°C on average. Does that seem right?
    • CommentAuthorjohnuready
    • CommentTimeFeb 15th 2015
     
    I will recheck the results when the unit is back together.

    I was concerned about a 3 degree temp difference between the outside temperature and the temperature at the MVHR. After checking the roof space under the insulation, the temperature held in the OSB airtight box and plasterboard (bungalow) you can feel the stored heat. Once I get more sensors in I can measure the roof space temperatures. Anybody else found 3 to 4 degree increase on incoming fresh air through a roof?
  1.  
    Posted By: johnureadyAnybody else found 3 to 4 degree increase on incoming fresh air through a roof?
    If you're bringing in air through the roof space and its gaining 4 degrees then you're cooling the roof space which increases the heat-loss from the house. Adding these 4 degrees to the efficiency of the MVHR won't give you an accurate efficiency reading. Some MVHR manufacturers use inefficient fans and add the heat-loss from the fans to their efficiency figures, which gives inflated efficiency results. The difference between lab results and in house results is often between 10-15%.
  2.  
    So can we trust the SAP numbers at least?
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