Switch Engineering was hired to redesign the boiler, hot water heating, and domestic hot water systems in a seniors residence built in 1982 managed by Vista Housing for Seniors. The project end goals were increased tenant comfort, better energy efficiency, and ease of maintenance. In the existing six-floor building, the boilers were two natural gas-fired SuperHot units that are less than 80% efficient due to their age. The domestic hot water heaters were also gas-fired, mid-efficient units.
Boilers operate in two ranges with temperature thresholds for condensing models and traditional models. The figure below shows that a traditional boiler can only ever reach about 88% operating efficiency at the appropriate inlet temperatures. However, using a condensing boiler can increase efficiency to approximately 95% efficiency. The figure below from ASHRAE displays these ranges.
Switch engineering suggested a cascading condensing boiler system to replace the existing gas-fired units at Casa Romana since the operating temperatures can support the high-efficiency models. The designed system has an efficiency of up to 94%. Since the boiler system is so efficient, we advised our client to install domestic water heaters that are in-direct fired through coils from the boiler hot water supply. We chose a dual coil system that increases recovery rates for performance and allows for a future solar water heating installation if the client decides to do so. The other opportunity to utilize the boiler efficiency is using a glycol loop to heat the building make-up air (MUA) unit, though this was not in the current project scope and budget. However, Switch Engineering ensured that it would be a smooth installation when the MUA is replaced. We specified a boiler manifold with the capacity for a 6th boiler so that when there is an increased heating demand for the glycol loop, the installation will not affect the existing system's operation.
Canadian Green Building Council (CaGBC) estimates that building energy consumption dedicated to space heating is 38%, and water heating is 8%. Space heating is the most significant energy end-use in buildings and therefore provides the biggest impact when performance is enhanced. First, a baseline was established for this building. The current annual energy use for space heating and water heating is 2,340 GJ using mid-efficient traditional gas-fired equipment at the end of life. With the new 94% efficient condensing boilers and in-direct coil water heaters, the new annual consumption for space heating and water heating projected at 1,870 GJ. This is equivalent to a reduction of 25.6 tonnes of CO2 released annually.
The energy savings and emission reductions are incredible. However, we realize that it also must make financial sense for our clients to implement high performing systems. There is a cost premium on the high quality German condensing boilers. The five condensing Viessmann boilers cost $66,148.00, not including any circulators or system accessories. Comparatively, two equivalent Super Hot Boilers is approximately $32,000.00 to meet capacities, not including circulators or accessories. The cost of natural gas is assumed to be $8.42/GJ as calculated using regression analysis to represent consumer cost from 2018 accurately. With an energy use reduction of 470 GJ annually, this equates to $3,957.00 in yearly savings.
Additionally, Switch Engineering advised our client to apply for Energy Efficiency Alberta's equipment rebates for systems like this. The models we have specified qualify for the rebates at an amount of $2,120.00 per boiler. This is a total return of $10,600.00 to offset the cost. Once the rebate is considered, the additional cost of upgrading to the high efficient system over the traditional one is $23,548.00. From energy savings alone, this is only a 6-year payback and extremely justified! A heating system upgrade often cannot be justified from energy cost savings alone. However, in cases like this, where equipment is at the end of life and must be replaced, the upgrade to high performing products is a great way to save and promote sustainability.
Operational ease and decreased maintenance result from high-efficiency technology; the control system and circulating equipment ensure that the systems are only running when there is a demand and use VFD pumps to conserve power. There is also increased redundancy with the cascading model. Not to mention the ability to have remote access to all the building controls through an internet connection.
Switch Engineering commits to sustainability in each project. We strive to go above and beyond to make efficiency attainable for all clients through innovative thinking.