Pre-occupancy testing

Pre-occupancy testing started when the CALA Hazledean house was opened as a show home in June 2007.

The main objectives were to  (i) thoroughly test the DBB roof system and (ii)the computer contrlled, real-time remote data monitoring equipment, to ensure that both worked effectively before the house was occupied. In addition, the fact that the house was at times not occupied allowed more intrusive tests, that would otherwise not have been possible , to be completed.

Thermal Imaging and air tightness

The objective of these tests was to complete partial and whole-house air tightness testing and to couple the results with thermal imaging of the roof, both internally (from inside the attic) and externally to see the effect of air as it is drawn in through the Energyflo™ cells. The air tightness test was used to establish whether the house was constructed to a level that minimised infiltration (unwanted airflows). Thermal imaging carried out in conjunction with pressure testing can give an indication of the heat that is radiating from a leak and through the envelope surface, and therefore some indication of heat loss.

Results from these test confirmed that the house was in fact well above the standard UK construction  for air tightness, allowing best use of the Energyflo™ cell and ensuring that the bulk of air flow can be channelled through the DBB system.

The results from thermal imaging can be seen in the pictures below. When the system is off (top) there is a noticeably brighter output to the roof indicating higher heat loss. This is reduced when the system is on (bottom) and would reduce further given time for the roof tiles to cool.






Particulate Matter (PM) filtration

There was also an opportunity to test air quality, by taking particle counts over a spectrum of size ranges. Outside air was sampled and also the air after it has passed through the Energyflo™ cells in the main supply duct. This collection point was selected so that sampling was for the whole system rather than an individual tray. The first result for cumulative mass of particulates is shown below.

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Pre and post filter micro particulate levels for Balerno system

Pre and post filter micro particulate levels for Balerno system
[Click image to enlarge]

This covers particle sizes in the range 0.23μm to 25μm. The sampling device, a portable GRIMM spectrometer, measured mass, which although very low to start with for a clean rural site, is significantly reduced as ventilation air moves through the DBB system.

Recent research has shown that PM2.5s, acting alone or in combination with gaseous co-pollutants, are likely to be causally related to observed ambient fine particulate levels and the associated health effects. It is therefore imperative in any particulate filtration system to consider the efficiency of collection in the sub-micron range. This was carried out using a TSi P-Trak nano-particle measurement device, which counts particle numbers in the 20nm to 1μm size range.

Outdoor air was found to have particulates with a maximum of 8892, average of 3673 and minimum of 2687 particles per cubic centimetre over the period of sampling. In comparison the duct readings gave maximum, average and minimum readings of 1324, 378 and 244 particles per cubic centimetre respectively. The average value was reduced by 90% on passing through the Energyflo™ cells.

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Pre and post filter nano-particulate levels for Balerno system

Pre and post filter nano-particulate levels for Balerno system
[Click image to enlarge]


The other important area of consideration in the pre-occupancy phase was the change in air temperatures that occurred as the air moved through the system.  Two plots of temperature versus time are considered in this section. The first shows temperature differences across the inner and outer surfaces of the Energyflo™ cell for a typical week in June. It shows the air temperatures before it passes through the cells (blue line) and again after the cells (red line). The calibrated temperature sensors were positioned in the airflows to either side of the dynamic insulation media in the Energyflo™ cells and shielded to minimise radiant effects. The plot shows that temperatures cycle on a daily basis and also alter with respect to external (solar) conditions.

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Graph of summer temperatures on the outer and inner sides of the dynamic insulation

Air supply temperatures before and after the Energyflo™ cells (summer).
[Click Image to View]

At night time, when external conditions are less dominant, the temperature gain was found to be between 2 and 4°C. This is a significant uplift to the temperature of air passing through the cells and indicates that a significant proportion of the heat being lost to the atmosphere is captured and returned to the house.

We can look at the thermal performance of the overall DBB system by considering the outside ambient temperature and the temperature of the pre-tempered air in the main supply duct – i.e., the temperatures before the outdoor air reaches the DBB roof system and after it passes through the system and is gathered together in the main supply duct leading to the MVHR unit. The difference between the outside and the inside is , on average, above 10°C for the same week in June. It should be noted that the indoor temperature can be surpassed during peaks due to solar gain.

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Outdoor to in-duct temperatures indicating whole system performance during summer

Air supply temperatures before and after the DBB system (summer).
[Click image to enlarge]

The roof-mounted DBB system thus combines conduction heat loss recovery with daytime solar gain. The air feed to the cells flows into the space under the roof tiles, which are dark and therefore good radiant energy absorbers. Solar gain is a very useful feature to harness in the Scottish climate, allowing the DBB system to offset heat lost through the conventionally insulated walls of the house using the surplus solar gain from the roof. This allows the system to perform above expectations but there could be a risk of overheating in the event of an exceptionally hot summer, with periods when cooling may be required.

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Sponsors The University of Aberdeen EBP Cala Carbon Trust