In January 2010 Envirogroup completed a design-built installation of the largest residential apartment DHW solar system in NZ.
Devon Park Apartments in Auckland consists of 57 apartment units within a 13-storey tower with adjoining 2-level townhouses. In 2007 Envirogroup designed and installed a replacement for the property’s old, inefficient and failing centralised, gas-fired domestic hot water system. When the opportunity arose to apply for an EECA fund, we conveyed our concept to this body corporate of complementing this system with solar hot water panels.
Our business case highlighted not just the more direct and tangible benefits expectable from a renewable energy-saving system like solar hot water but also the fact that a successful outcome would provide an ideal case study to advocate solar installations in many other residential buildings of similar type and size .
The system proposed consisted of 27 high efficiency evacuated tube solar panels with a total collectors’ area of more than 90 m2;
considering that in a residential installation the total area of the roof panels is typically between 2.5 and 4 m2, the system was comparable in performance to 20-30 single domestic installation but at a considerably less cost with no duplication of many other solar components except the solar panels.
The project received 50% funds from the EECA Innovation Fund Scheme and we were required to install, commission, monitor and report monthly on the system performance as part of the contractual agreement.
Initial analyses were based on a combination of gas & electricity accounts, newly installed hot water meter and electricity meter to the pool heat pump as well as data collected via the SolaData monitoring software.
During the first three months of full load operation our analysis showed an average 11% reduction in gas consumption (fig. 1) due to the solar contribution with a slightly decreasing trend (from 12% to 10%) as we approached the winter season but this was in line with seasonal expectations.
After the initial energy consumption calculations two of the four continuous flow gas water heaters were turned off to duty cycle the units and take advantage of the solar gain while at the same time help extending the life of the equipment by 50%. This decision was supported by the evidence that two units were coping well with the building demand during summer conditions and although in winter we noted that the units were working slightly harder to maintain the DHW temperature, there was sufficient buffering and DHW capacity to maintain adequate supply so the 4-unit operation was not resumed.
The gas savings over the monitored year reached a peak of 31% in July,
which we attributed to a combination of increased solar radiation (confirmed by NIWA data) and a concurrent (though apparently unexplained) reduction in hot water demand. In summer 2011 the savings recorded were 29% of the 2009 baseline consumption.
As per electricity, the absence of historical consumption data for the pool heat pump meant that we could only estimate savings based on power bills and simulation software calibrated on known pool data and sound engineering assumptions.
The initial results showed an electricity reduction of 11% and although data referred to many and diverse electricity end users (common area lights and lifts for example) we knew that the only change in circumstances was the solar contribution to the pool heat pump. This same trend was observed in the following summer months when the pool was operational again after winter shut down.