Energy and comfort transformations in multiresidential buildings

by nithya_caleb | December 11, 2018 11:39 am

by Olivier Matte, Ekaterina Tzekova, PhD, and Keith Burrows, LEED AP

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The Atmospheric Fund (TAF) and Ecosystem have partnered with Toronto Community Housing Corporation (TCH) to perform energy retrofits on seven multi-unit residential buildings (The Toronto Community Housing Corporation (TCH) manages more than 2100 buildings in Toronto. Founded in 1991, The Atmospheric Fund (TAF) invests in urban low-carbon solutions in the Greater Toronto and Hamilton Area to reduce carbon emissions and air pollution. Ecosystem is a fully integrated design and construction engineering firm specializing in buildings’ energy ecosystems.). These retrofits, which are part of the TowerWise program, have reduced annual utility bills by $492,000 and carbon emissions by more than 920 tCO₂eq per year, while addressing thermal comfort and ventilation issues for residents.

Maintaining housing affordability and indoor comfort while addressing high utility costs is an ongoing challenge for multiresidential building (MURB) owners. Through the TowerWise Retrofit Project, TCH saw a great opportunity to address these high utility costs (pre-retrofit energy use intensity was 284 to 318 ekWh/m²) as well as commonly experienced operational challenges such as year-round thermal comfort and poor ventilation.

Finding the right partners

TCH and TAF identified seven buildings within TCH’s portfolio that would benefit from deep energy retrofits. These sites were chosen based on their varied building form (low-, mid-, and high-rise) and occupant profiles (individuals, families, and seniors). Together, they contain more than 1200 units.

TAF and TCH issued a public request for proposal (RFP) in October 2014 with the goal of finding a design-build firm that could maximize project outcomes and utility cost savings. Rather than specifying desired equipment, systems, or services, TAF and TCH issued an outcomes-based RFP, providing bidders with the option of developing solutions to best achieve the desired project outcomes such as:

• improving tenant comfort by enhancing indoor environmental quality;
• decreasing greenhouse gas (GHG) emissions by 30 per cent;
• reducing energy consumption and utility costs by 20 per cent; and
• minimizing annual operations and maintenance costs.

The goal was to work closely with a firm that could effectively capture the needs of a range of stakeholders—including tenants, building superintendents, TCH Smart Buildings and Energy Management unit, and building operations/maintenance teams—using an integrated approach. Given the nature of this performance agreement, the bidders also needed to guarantee the expected utility cost savings and financial incentives, as well as monitor and verify the savings during the agreement period.

Maximizing outcomes

The winning firm, Ecosystem, a Canadian design-build company, began the project with an extensive energy audit of all the seven buildings. Next, the team undertook several design charrettes to discuss and prioritize the retrofit solutions. These meetings included a variety of project stakeholders (TAF, Ecosystem, TCH, energy management and facility maintenance teams, and building superintendents) and industry experts. The project team also took advantage of this integrated design process to collect energy and indoor environmental quality information to help prioritize the energy retrofit measures.

After a six-month analysis, the project team finalized the following energy retrofit measures:

• installing 3-L (0.8-gal) low-flow water closets;
• converting interior and exterior light fixtures to light-emitting diode (LED) luminaires;
• installing motion sensors in underground garage bays, garbage rooms, and mechanical rooms;
• cleaning radiators;
• installing condensing boilers with high modulation capability (a condensing boiler is a high-efficiency [typically over 90 per cent efficiency] boiler, most often producing hot water. It is designed to condense water vapour in the exhaust gases and, by doing so, it recovers the latent heat of vapourization, which would otherwise have been wasted);
• using gas absorption heat pumps for domestic hot water;
• cleaning of fresh air supply and return ducts;
• installing new makeup air units with heat recovery and variable frequency drives (a variable frequency drive [VFD] is an electronic component that controls AC motor speed and torque by varying the frequency and voltage of the electricity input. By doing so, a VFD allows for matching the motor energy consumption to the real-time needs in the building, so the motor does not have to run at 100 per cent speed all the time. A VFD is installed upstream of the motor’s electric input.);
• modulating booster pumps for domestic water; and
• installing new in-suite smart thermostats.

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Getting a head start

Given a tight construction timeline of nine months, the project team leveraged the flexibility of an integrated project delivery approach and began with implementing the simplest measures such as water closet replacement and lighting. During this time, the design was fine-tuned for the more complex heating-related measures.

Work got underway in May 2016, with the installation of more than 1200 new high-efficiency, 3 L water closets. To assist with these installations as well as other in-suite measures, the project team engaged Building Up, a nonprofit social enterprise creating green employment opportunities for individuals experiencing barriers when entering careers in the building industry. This project employed more than 12 community members for an equivalent of 1650 person-hours. Overall, replacing the water closets has resulted in saving more than 53,600 m³ (1.9 million cf) of water (equivalent to a 27 per cent reduction) and $189,000 in utility savings over the first year of performance. Actual savings significantly exceeded projections because the new water closets are equipped with valves rather than flappers, a source of continuous water leakage with older models.

The lighting upgrades included a complete conversion to LED. Common areas, as well as underground garages and outdoor lighting, were changed in 2016. Rather than a one-for-one replacement, an improved fixture configuration resulted in better lighting uniformity in corridors.

To further reduce energy waste, motion sensors were installed in the underground garage at the two high-rise buildings, which resulted in an 88 per cent electricity consumption reduction. Improved quality and intensity of light, along with the automated “on/off” switching provided by the motion sensors, increased the feeling of security in the garage and in the outdoor areas.

Upgrading water heating equipment

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Changing boilers should never be seen as a simple, one-for-one replacement. In addition to installing highly efficient condensing boilers, these retrofits needed to ensure the equipment is within the condensing temperature range for the majority of time. The project team achieved this by improving radiator controls for residents, which helped reduce the overheating and resulted in fewer windows being opened during the winter. The piping was also modified to ensure the lowest possible return temperature to the boiler room. Reducing energy waste in the units and across the hot water network allowed for optimal sizing of the new heating equipment. The project team reduced the total heating capacity and installed condensing boilers with high modulation capacity to ensure the building supply was better aligned with actual demand. Figure 1 shows the pre- and post-retrofit heating capacity at each site.

At the two low-rise buildings, two new condensing boilers were installed, sized to handle most of the heating load, aside from the coldest days of the winter. In this case, one of the old boilers is enough to supply the remaining load. Two new air-source gas absorption heat pumps (GAHPs) were also installed to produce domestic hot water. They have been sized to provide about 60 per cent of the hot water load, ensuring a fairly constant operation. The new condensing boilers are designed to meet the remaining load.

The GAHP technology uses natural gas to drive the refrigeration cycle. They are more efficient than condensing boilers, achieving operational efficiency in excess of 100 per cent. In Toronto, GAHPs are significantly less expensive to operate than their electric heat pump counterparts.

The two GAHPs have performed well, with an average daily coefficient of performance (COP) of 1.14 for the period of November 2017 to May 2018, and an average COP of 1.24 for the warmer months of May and June. Although GAHP efficiency degrades in cold ambient temperatures (as with electric air-sourced heat pumps), daily COP values exceeded 1 throughout the winter. Compared to the original boilers at the site, the GAHPs saved approximately 3360 m³ (118,657 cf) of natural gas since November 2017, and TAF projects they will save 8400 m³ (296,643 cf) of gas and over 15 tCO₂eq of carbon emissions over a one-year period.

At one of the two high-rise buildings, two of the four existing boilers were replaced with new condensing boilers. One is mostly dedicated to domestic hot water heating, enabling it to maximize time spent within the condensing range. The second boiler is dedicated to space heating.

The other high-rise building did not need major equipment upgrade, but it underwent an extensive recommissioning process.

By September 2017, the central space heating boiler room at the mid-rise building site was undergoing major renovation. The two existing boilers were demolished and replaced by three new condensing boilers. These boilers required a new lining in the existing chimney. This required a crane to lift 33.5-m (110-ft) lining sections in the air, before sliding them down the existing chimney stack. This boiler room upgrade was the last one to be completed ahead of the December 2016 deadline.

Across all three sites, the condensing boilers were sourced from the same manufacturer to simplify ongoing maintenance.

Bring in the fresh air

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In October 2016, the project team focused their efforts on improving the ventilation systems for the mid- and low-rise sites, which, like most other multiresidential buildings, suffer from under-ventilation in the corridors.

Pre-retrofit testing revealed the fresh air supply rates were 43 per cent below capacity across the sites. Additionally, pre-retrofit surveys revealed 49 per cent of the residents were bothered by odours from neighbouring units on a daily basis.

At the low-rise site, the fresh air supply and return duct systems were cleaned, including the fire dampers in the bathrooms. Existing rooftop units were replaced by two new units with natural gas burners and energy recovery wheels capturing heat from the exhaust. The fans were also equipped with VFDs to modulate according to the occupancy schedule (An energy recovery wheel [or thermal wheel] is a porous heat and enthalpy recovery component in a ventilation system, which is half exposed to the exhaust air stream, while the other half is exposed to the fresh, outside incoming air stream. By continually rotating, the wheel captures some of the heat and humidity from the exhausted air and transfers it back to the fresh incoming air. In the winter, this reduces the cost of heating and humidifying the air, and in summer, it contributes to preserving the coolness in the building.).

At the high-rise buildings, only the supply ducts were cleaned, as there are no central exhaust ducts (kitchen and bathroom exhaust directly to the exterior). The absence of centralized exhaust ducts also influenced the selection of the new rooftop unit, which includes VFD on the supply fan. Cleaning at both of these sites resulted in indoor air quality (IAQ) improvements, noted by building site staff and residents. With the new makeup air units, fresh air supply now meets the requirements of the American National Standards Institute/The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ANSI/ASHRAE) 62.1, Ventilation for Acceptable Indoor Air Quality.

The reported frequency of unwanted odours has since significantly decreased: there was a 31 per cent decrease in odours from neighbouring units, 28 per cent from own cooking odours, and 20 per cent from outside odours.

LESSONS LEARNED

Key takeaways from the TowerWise Program in Ontario are: Projects need to clearly define the desired outcomes. It is critical to define the “what,” and not the “how.” Project partners must commit to the results and outcomes. Favour an integrated project delivery approach that allows relevant stakeholders to collaborate as early as possible in the planning/design process. A longer design phase can save time and money during the construction process. A whole building approach, targeting multiple measures across different systems, can maximize the expected outcomes. This is also a perfect opportunity to address capital repair/renewal priorities. When working with tenants, proper communication of the retrofit measures and their expected benefits can make it easier to implement in-suite measures. This engagement is also an opportunity to teach residents about energy saving behaviour that can also improve their comfort and satisfaction.

 

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Modulating the domestic water booster pumps to match the demand

Another energy conservation measure implemented was the installation of VFDs on domestic water booster pumps for the low- and mid-rise buildings. Previously, the pumps ran continuously, regardless of the domestic water demand from the units—thus wasting energy. Coupled with pressure sensors in the network, the VFDs now allow pumps to reduce their speed and energy consumption to perfectly match the actual pressure needs in the building.

Giving tenants control over comfort

Aside from the ongoing centralized control sequence optimization, one of the last measures implemented was the installation of smart thermostats in suites across four of the seven buildings. Each thermostat controls a new valve that was installed in each unit, controlling water flow to the radiators.

Pre-retrofit, the lack of heating control in each unit as well as oversized mechanical systems with poor modulation capability often resulted in high indoor temperatures, resulting in residents opening their windows even in winter.

Post-retrofit, the thermostats helped maximize space heating efficiency improvements by allowing residents to control their own interior temperatures. Resident surveys conducted in March 2018 showed a reported decrease of (39 per cent) windows opening during the winter, indicating this measure is improving tenant comfort and reducing energy waste. Additionally, interior temperatures in units decreased by approximately 2 C (3.7 F) on average, while extreme overheating (with units exceeding 28 C [84 F]) decreased by 31 per cent. Overall this thermostat measure has not only maximized the expected space heating savings, but also improved tenant comfort and satisfaction.

Having specific heating controls in these units also enables the decrease of the return hot water network temperatures. This helps to maximize the amount of time the new boilers are within the condensing range, ultimately increasing the overall efficiency of the heating network.

Extensive recommissioning

One of the two high-rise buildings recently received an upgrade of its heating and domestic boilers, but needed recommissioning to operate these systems effectively. Ecosystem optimized the boiler room controls logic to make sure the new boilers could condense whenever possible and pumps could be shut off when not needed. This ultimately improved the thermal comfort and the resident satisfaction.

The end of the project placed emphasis on providing proper training to the facilities maintenance team as well as the buildings’ superintendents. The comprehensive training program was tailored to address each group’s particular considerations. A reference manual, complete with all the final specs and drawings, operation and maintenance procedures, required replacement parts to stock, and equipment guarantees was provided for each site.

Achieved outcomes

This project has achieved more than $492,000 in utility cost savings over the first performance year—22 per cent greater than the expected savings. This is mostly due to higher-than-expected water and electricity savings. Ecosystem also designed the project to maximize financial incentives, which reached $332,000.

Water consumption was reduced by 53.6-million L (14.2 million gal) over the last year (a 27 per cent reduction), while electricity consumption was reduced by 1190 MWh (a 64 per cent reduction for common areas), and natural gas consumption by 370,000 m³ (13 million cf), a 22 per cent reduction. Further, carbon emissions have been reduced by 920 tCO₂eq per year (a 26 per cent reduction).

Thanks to an integrated approach to the project, TCH was able to operate the buildings throughout the implementation process. With the design-build firm accountable for providing comfortable indoor environmental conditions, proper control of the systems was performed throughout the entire construction period. These efforts were also maintained during the measurement and verification process, enabling the team to keep optimizing the systems after project completion, and exceed expected results.

INTEGRATED PROJECT DELIVERY APPROACH

[6] A whole building, integrated project delivery approach was key in achieving the goals of the TowerWise project. This outcomes-based approach allows the design-build firm to spend more time in the detailed study phase, seeking more information from both the building and the people operating it, to come up with the best optimized solutions for meeting the client’s desired outcomes. For the low-rise buildings, this translated in building improvements covering most of the HVAC systems, including the addition of new, properly sized space heating boilers and domestic hot water gas absorption heat pumps, new air handling unit (AHU) with heat recovery and variable frequency drivers (VFDs), conversion to light-emitting diode (LED) light fixtures, new valves on radiators along with electronic thermostats, optimized control sequencing, and new high efficiency water closets

Engaging residents

Aside from the technical challenges posed by such a project, co-ordination with residents required additional skills and flexibility. Proper communication was key to ensure residents were on board with the in-suite measures. Communication initiatives informed tenants about the upcoming improvements as well as the benefits that could be realized. Lobby posters, easy to understand measure notices, and translated materials were all used to educate residents about the type of work happening in their buildings as well as the comfort improvements they could expect. A key engagement piece focused on the in-suite smart thermostats where residents were taught not only how to use the thermostat, but also energy saving behaviour that will improve their comfort.

[7]Olivier Matte is development manager at Ecosystem. After receiving a bachelor of mechanical engineering degree in 1999, Matte joined the Ecosystem team in 2003 as a project development engineer. An excellent communicator, Matte is responsible for staff training and occupant awareness. To date, Matte has trained staff in four colleges, 17 school boards, and 24 hospitals. He has also created and co-ordinated 18 awareness campaigns for Ecosystem’s health and education clients, reaching nearly 35,000 people. Matte also educates the market about energy efficiency solutions by contributing to articles and videos. He can be reached by e-mail at olivier.matte@ecosystem.ca[8].

[9]Ekaterina Tzekova, PhD, is the low carbon buildings manager at The Atmospheric Fund (TAF), overseeing the energy efficiency demonstration work. Tzekova has published widely on topics related to sustainability, building energy performance, material durability, and indoor environmental comfort. She is a voting member on the National Research Council’s (NRC’s) Canadian Commission on Construction Material. Tzekova can be reached at etzekova@taf.ca[10].

[11]Keith Burrows, LEED AP, is the energy and indoor environmental quality (IEQ) research co-ordinator at The Atmospheric Fund (TAF), responsible for analyzing building performance and indoor environmental quality data for the TowerWise retrofit program. Burrows holds master’s degrees in computer science from Boston University and sustainable design studies from Boston Architectural College. He can be reached at kburrows@taf.ca[12].

Source URL: https://www.constructioncanada.net/energy-and-comfort-transformations-in-multiresidential-buildings/

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