MVHR RESEARCH FOR EXISTING HOMES
What we observed Installing an MVHR system in a ‘leaky’ dwelling increases the building’s energy requirements because it increases air change rates. The extra air needs to be heated to maintain the internal temperature – although this will be partially offset by heat recovery. Figure 2 shows this increased requirement for the test house, relative to natural ventilation, at air permeability values of 10 and 7m3
/(h.m2 ) @50Pa.
With an MVHR system specified to minimum building standards, it is necessary to improve the airtightness to 3m3
/(h.m2 )
@50Pa. At this level, the reduction in space heating energy exceeds the energy expenditure required to operate the system.
10 9 8 7 6 5 4 3 2 1
0 10
Natural ventilation
10 7 5 3 1 0.6 10 7 5 3 1 0.6 MVHR Minimum building standards Building air permeability (m2
MVHR Best practice standards /h.m2 @50Pa) n Space heating n Auxiliary Figure 1: Modelled annual space heating and auxiliary energy consumption of the E.ON Retrofit Test House 0.63m3 /(h.m2 /(h.m2 ) @50Pa, corresponds to the Passivhaus standard of 0.6 ach-1 @50Pa after
conversion of units. The mid-range value, 5m3
) @50Pa, represents the measured
air permeability achieved by the test house after extensive draught-proofing work. For each level of airtightness, two MVHR systems were simulated: one specified to minimum building standards, with a specific fan power of 1.5W/l/s and heat recovery efficiency of 70%; and the other to best practice standards, with a specific fan power of 1W/l/s and heat recovery efficiency of 85%.
The annual energy consumption and CO2 emissions were calculated and compared with the simulated naturally ventilated test house – which has kitchen and bathroom extractor fans but no MVHR – at an air permeability of 10m3
/(h.m2
www.cibsejournal.com ) @50Pa.
2250 2000 1750 1500 1250 1000 750 500 250 0
10
Natural ventilation
10 7 5 3 1 0.6 10 7 5 3 1 0.6 MVHR Minimum building standards
MVHR Best practice standards Building air permeability (m2 /h.m2 @50Pa) n Space heating n Auxiliary Figure 2 shows that an air permeability of 1 m3 /(h.m2 building standards to achieve an overall reduction in CO2
) @ 50Pa is needed for an MVHR system specified to minimum emissions.
It should be noted that the MVHR system
uses electricity to operate, which is more carbon-intensive than the mains gas used for the space heating system. This means that a greater reduction in space heating energy is needed to offset the increased electricity consumption and ensure an overall reduction in CO2
emissions.
For the system operating to best practice standards, the researchers found that energy savings and CO2
emission reductions were
achieved at air permeability values of 5 and 3m3
/(h.m2 ) @50Pa respectively. In other
words, energy savings can be made at a slightly poorer level of airtightness than with the MVHR system operating to minimum building standards. This suggests that in
September 2013 CIBSE Journal 37
51
Annual CO2
emissions (kg CO2
)
Annual energy consumption (MWh)
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76