Helping Set The Benchmark In Sustainable Building
100 Bishopsgate, is a prestige building in the heart of the financial district of the City of London. Operated by Brookfield Properties, the development is a stunning all-glazed tower offering 37 floors of mixed use. Designed and constructed to meet the highest standard of efficiency, it has achieved an ‘Excellent’ BREEAM rating to maximise sustainability and reduce the carbon footprint over the lifetime of the building.
As part of this process Adveco worked with design authority Hilson Moran and consultants Michael J Lonsdale on provision of the building’s hot water. Adveco’s application design team was tasked with meeting the separate needs of Brookfield Properties and its tenants, with plant facilities that would be built around A.O. Smith BFC high-efficiency gas water heaters. In addition, a roof-top site would allow for the installation of a solar preheat system with dedicated water heaters.
The solar preheat system consists of roof-mounted solar collectors with integrated drain back for overheat protection. The collectors feed a 500 litre IT indirect water heater. Here the solar energy is accumulated, with the IT acting as a dedicated solar store providing preheat which then feeds a pair of BFC80 fully room-sealed condensing high-efficiency (97% gross) gas fired water heaters.
The solar system uses a smart differential temperature controller to manage the solar station pump. This controller activates the pump when the solar collector sensor temperature is higher than that of the solar preheat sensor. Heat is transferred from the collector to the preheat tank coil until the tank reaches its set-point reading, or if the solar intensity drops and the collector cools to the Preheat temperature.
Smart solar control also enables the exchange pump to be used to transfer heat from the solar preheat to the water heater in periods of low DHW usage. This balancing is critical if the solar thermal system is to operate efficiently without wasting generated energy. The solar control will sense if the preheat tank reaches 70°C and, if the monitored after-heater temperature is less (60-65°C), the exchange pump will be activated forcing preheated water to the BFCs. The pump turns off once the pre-heat temperature drops to 60°C. This ensures that the solar energy is used most advantageously, effectively turning the IT tank into a combined solar preheat, extending the pre-heat volume and allowing efficient use of solar energy. Without this balancing, the thermal losses could be equivalent to turning off half of the building’s solar thermal collectors.
The solar thermal system also offers ongoing monitoring for improved management with a volt free alarm contact on the BFCs for general fault indication on the BMS. Each roof mounted solar collector bank is also dedicated to one solar coil to allow uninterrupted drain back for stagnation protection. Should demand for DHW drop, solar thermal collectors can, unless drained, be prone to stagnation where the solar fluid overheats and takes on the consistency of tar within the collector. This requires a lengthy cleaning process and can causes considerable damage requiring costly repairs. At 100 Bishopsgate, when the preheat tank reaches 70°C, the solar pump stops, and the natural head of solar fluid flows in reverse back into the coil port and fills the drain back tank, emptying and protecting the solar collector.
At 181 metres in height, available roof space for solar thermal is ultimately limited in comparison to the total square footage of the building and the numbers of people occupying the building. To address periods of high DHW demand, where solar thermal cannot meet all the building’s requirements, Adveco designed, supplied and commissioned an application based on a series of A.O. Smith BFC Cyclone condensing gas water heaters.
Fully room-sealed, and with versatile flue options, this water heater can be placed almost anywhere, in this case in plant rooms located on the building’s lower floors. Perfect for the provision of large scale, near instantaneous hot water demands, the BFCs are fitted with an automatic gas/air premix burning system including burner modulation, which enables the BFC to be highly efficient (97% gross). Despite using natural gas, this level of efficiency helps support the buildings BREEAM rating. With the BFCs connected into the BMS, the building management team can monitor almost 50 parameters from temperatures in the appliance to burning hours, allowing for greater control and a more cost-effective option for delivering peak hour demands for hot water when compared to electrical energy.