Evaluating a proposed retrofit measure for a multi-unit residential building which uses an air-source heat pump operating in an enclosed balcony space

To improve the energy performance of Toronto's post-war multi-unit residential buildings (MURBs), these buildings must be energy retrofitted. Here, a novel energy retrofit strategy employing air-source heat pumps (ASHPs) operating in enclosed balcony spaces is assessed. The enclosed balcony provides a thermal buffer zone (TBZ) which can improve the coefficient of performance of the ASHP compared to typical exterior operation by accessing captured solar gains. The estimated energy savings associated with implementing this retrofit strategy was determined using a hybrid modeling approach. A calibrated energy model of a 1968 MURB represented the base case energy consumption. Then, a supplementary algorithm, developed based on laboratory testing, was used to determine the quantity of energy that could be extracted from the TBZ and delivered to the north- and south-facing suites as well as to hot water storage. The modeling exercise yielded estimated whole-building energy and greenhouse gas emissions savings of 39% and 45%, respectively. Due to utility prices at the time of writing, the energy cost savings do not present a compelling financial case. However, the qualitative benefits of this retrofit strategy include suite-based control for occupants and the ability to sub-meter space heating energy use at the suite-level

Testing and simulation of a low-temperature air-source heat pump operating in a thermal buffer zone

Air-source heat pumps (ASHPs) are commonly used in temperate climates throughout Europe and Asia to provide energy efficient heating and cooling. However, ASHPs have not been widely adopted for heating in colder climates because the coefficient of performance (COP) is lower when outdoor temperatures are colder. While many researchers are working on improving the cold-temperature performance of ASHPs by altering the design of the equipment, this work examines an innovative way to improve performance by operating an existing ‘off-the-shelf’ ASHP within a thermal buffer zone. This paper shows that operating an ASHP in a thermal buffer zone (TBZ) created by an enclosed balcony space can improve the COP in cold temperatures. An ASHP operating in a TBZ was tested in a climate chamber where the performance was monitored under a variety of climatic conditions. The temperature drawdown of the TBZ and the associated impact on the COP were observed. The TBZ solar heat gain rates required to improve the COP were identified for a range of exterior temperatures. Then, a suite-based energy model was developed and calibrated to simulate the performance of the ASHP operating in the TBZ. The model provided a reasonable prediction of the ASHP performance below 10 °C

Using suite energy-use and interior condition data to improve energy modeling of a 1960s MURB

Energy modeling is a useful tool for evaluating the performance of contemplated building energy retrofit measures. Traditionally, energy models are developed using data collected from building floor plans and site visits and are then calibrated using utility bills. In the work presented here, an energy model for an existing multi-unit residential building (MURB) was developed using this traditional approach. Next, a refined approach was taken. Using data gathered from a suite-based monitoring program, input data uncertainties in the energy model were addressed. Data from one year of monitoring were assembled to characterize the actual building performance and to calibrate this refined energy model. In order to identify which parameters could be used to improve the model accuracy, the output of this refined model was compared to the output from the traditional modeling approach. It was found that the interior temperature measurements and the sub-metered suite electricity use were the most beneficial in refining the energy model. However, other data collected including window operation and differential air pressures were useful for determining how the building was operating. The use of a local weather file generated from a roof-top weather station has also been discussed

Correlating energy consumption with multi-unit residential building characteristics in the city of Toronto

Multi-unit residential buildings (MURBs) in City of Toronto, Canada, contain more than half of the dwellings in the City and are responsible for a significant proportion of the greenhouse gas (GHG) emissions associated with building energy-use in the residential sector. To efficiently reduce the impact of this sector, MURBs with the highest energy intensity need to be identified. Accordingly, this study examined correlations between building characteristics and energy use. A wide range of energy intensities were revealed and it was found that typology-specific energy-use trends could not be established. The energy intensity variability was attributed to differences in building operation and it was suggested that many buildings can realize improved energy performance by changing operating procedures. The building characteristics exhibiting the strongest correlations with energy use were fenestration ratio and boiler efficiency. However, the need for more uniform and complete building characteristic and energy use data was identified. This study concludes with recommendations to improve the quantity and quality of MURB energy-use data and building characteristics so that researchers can develop a more accurate and complete picture of the MURB energy-use in Toronto

Exceeding the Ontario Building Code for low-rise residential buildings: Economic and environmental implications

The residential sector accounts for approximately one fifth of Canada's secondary energy use and greenhouse gas emissions. Thus, addressing the energy efficiency of residential buildings has a significant role to play in reducing the nation's overall greenhouse gas emissions. The Ontario Building Code has recently been updated to reflect a more stringent energy performance standard. A home built to the prescribed minimum requirements will perform at a relatively high standard with respect to energy use when compared to homes built less than a decade ago. This paper explores three energy efficiency upgrade options which improve upon the energy efficiency of the 2012 Ontario Building Code. The “controlled ventilation” upgrade involved tightening up the building envelope and adding heat recovery to waste air streams, and two additional upgrade options were developed to meet the high performance targets of the R-2000 standard. While the upgrades explored did not show financial benefit for individual homeowners at current utility rates, if the benefits to society are considered, the upgrades are an economically efficient method of reducing greenhouse gas emissions owed to energy consumption. In addition to highlighting the need for a broader approach to the cost-benefit analyses associated with these types of upgrades, this finding also warrants a discussion about how to transform the current housing market so that energy efficient homes are more appropriately valued

Decoupling of building energy use and climate

Energy use intensity (EUI) and climate have a well documented correlation, which is generally applied in building energy management. Green buildings have sought to greatly reduce energy consumption and a number of examples are documented in the literature. A sample of high performance buildings constructed in a variety of global locations is analyzed here, and provides evidence that measures to reduce energy consumption have reduced EUI to the point where its correlation with heating degree days is no longer apparent. This result suggests that end-user behaviour is the next major hurdle in lowering the energy consumption of greener buildings