As noted previously, Arborus has been researching low carbon space heating strategies for the Ontario building market, and will soon present a white paper on the subject at the SBE 2016 Conference in Toronto on September 19th and 20th of this year.
Arborus’ low carbon heating concept is based on using low carbon energy from the electricity grid to heat a commercial building in a heating-dominated climate. In Ontario, the lowest carbon option for heating commercial buildings using utility supplied energy is through the use of off-peak electricity. The average winter off-peak GHG intensity is in the range of 20 to 42 g/kWh as compared to 179 g/ekWh for combustion of natural gas.
The GHG impact from building heating can be easily reduced by close to 90% through better building design and the use of low carbon energy in off-peak hours from the electricity grid. In order to capitalize on this low carbon energy, the use of thermal energy storage is required. The proposed strategy utilizes water/mass storage in combination with the building mass to serve day-time heating needs.
Our test case is a two-storey commercial office building with a gross floor area of 2,200 square metres. By upgrading the envelope to R-30 walls, an R-40 roof, and high efficiency double-glazed R-2.6 windows (U = 0.38) – easily achieved at relatively low cost in today’s market – the peak heating load is reduced and thermal comfort is improved. Reducing the peak heating load allows low temperature water to be used for heating which greatly expands the available options for heating systems. For example, one can use in-floor radiant heating with water temperatures less than 49ºC. In a building heated with natural gas, this strategy allows condensing boilers to operate with much higher efficiency as a higher fraction of the water vapour in the exhaust gases condenses at lower water temperatures. More importantly, this reduction in the space heating load expands the practical range of heating technologies such as heat pumps, renewable sources such solar thermal, and refrigeration heat recovery. It also reduces the thermal storage capacity required to heat the building throughout the daytime hours.
By using radiant heat, we can also decouple the ventilating system from the heating system and use a dedicated outdoor air system (DOAS) to provide fresh air to the building. This decoupling significantly reduces the supply air flow rate from 9,500 to 1,300 litres per second and saves fan energy. Use of a DOAS also allows the building to control outdoor air delivery to meet demand, and provides higher ventilation effectiveness. This improves indoor air quality for building occupants while saving energy. An additional benefit of DOAS systems is that they allow heat recovery ventilating systems to operate at a much higher operating efficiency, further reducing the heating energy required to heat outdoor air before it is introduced into the building.
The proposed design strategies to improve the building’s heating and ventilating performance reduce GHG emissions by 57%, as compared to a “Code” building. The passive load reduction process minimizes the building’s heating requirements which further minimizes the amount of daily thermal energy storage required. Storage options are available which can store heat at night to be unlocked the following day to supply a large fraction of the heating energy required. Weather forecasting can be used to modulate storage to match the anticipated demand. Using thermal storage and switching from natural gas to off-peak electricity reduces GHGs by an additional 32.4% to nearly 90%.
The best energy saving strategies offer multiple benefits that go beyond energy savings and GHG reductions. Designing a building for low carbon heating offers significant benefits, including improved occupant comfort and satisfaction, better indoor air quality, and a corresponding potential for decreased absenteeism and higher productivity. These additional benefits deliver human health and financial benefits that go well beyond those realized by energy cost savings.
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