Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



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.

Buy individually or both books together. Delivery is free!


widget @ surfing-waves.com




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




    • CommentAuthorGotanewlife
    • CommentTimeJul 7th 2013 edited
     
    Struggling to compare various smaller HR units. Some just say "Efficiency 92%" and have a balanced flow, that I can compare but when for example a Unit says "Temperature Efficiency up to 70%" and gives as 1 of its max performance as "Supply 253 and Extract 371 m^3/h", that worries me! (the latter Unit being the Vent Axia HR200V), what does this mean?

    OK I understand that efficiency includes an element related to the energy required/gained to change the Relative Humidity but in terms of comparison that isn't important - just as well as I am never going to have the time to get to grips with that!!! So, should I run a mile from the HR200V?
  1.  
    Ahhh just found this:

    "The unit should retain up to 70% of the temperature differential of out going air" this appears to be Vent Axia way of avoiding the question!! This on the VA Integra - and on Max is extracts 49l/s but used 182 watts giving a SFP of 3.7! Crikey!
    • CommentAuthorjms452
    • CommentTimeJul 8th 2013
     
    Efficiency should include the effects of the latent heat recovered from water vapour in the internal air. Efficiency will drop as the internal air gets wetter.

    'Thermal Efficiency' is like assuming the air is dry and is fair enough for most purposes. You can tell it is not a real efficiency as you will find graphs of thermal efficiency going up to 100% when the air inside is at high RH and its cold outside.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJul 8th 2013
     
    Probably comes from the mathematics behind it and then converted to a fraction and then a percentage (why Tony hates percentages)
    http://www.engineeringtoolbox.com/overall-heat-transfer-coefficient-d_434.html
  2.  
    It seems likely that the 'temperature efficiency' is a fudge which doesn't take into account the energy transfer and makes the Vent Axia system look better than it is. Since the Vent Axia extract is greater than the supply more energy is extracted than retained even if the temps of both flows are the same. So the actual efficiency is 253/371*0.7 which is just below 0.5.
    • CommentAuthorGotanewlife
    • CommentTimeJul 8th 2013 edited
     
    Posted By: piersadlermakes the Vent Axia system look better than it is

    Well I couldn't work out why but for sure something smelled fishy, so I ran my mile and bought something else:wink:

    Now I have found:
    Thermal energy recuperating efficiency up to 68%

    Which I think is not a fudge just poor translation from Ukraine but also the same unit is described as:

    Moisture recuperating efficiency: Up to 65%

    It didn't bother me and I bought it!
Add your comments

    Username Password
  • Format comments as
 
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press