< Previous20 Fall 2019 • Ontario Building Envelope Council Investigating Confused Spaces: A Case Study In most buildings, the separation between indoor and outdoor space is easy to iden- tify. A wall, floor, or ceiling makes a clear distinction between the warm, toasty indoors and the cold, blustery outdoors. If parts of the building envelope are missing or do not function, the distinction between indoors and outdoors can get fuzzy. This becomes a “con- fused space,” requiring some investigative analysis to understand whether it should be inside or outside. Confused spaces are often found in parking garages, crawl spaces, and attics—areas that can blur the line between indoors and outdoors. A CONFUSED SPACE The subject property had a confused ser- vice space in the P1 level ceiling of a parking garage in a high-rise condominium. The ser- vice space contains a multitude of plumbing and HVAC equipment for the swimming pool directly above, and the hot tub tank was visible from within this space. Fin tube radiators provided supplemental heating for this space. Insulation was installed on top of the ceiling tiles, which formed the bottom surface of the space. The ceiling tiles were vinyl-faced to provide a smooth white surface to the parking garage below. The service space contained ductwork for the pool dehumidifier that maintained the relative humidity of the room. The ductwork took air from the pool down to the dehumidi- fier equipment located on the P1 level and sent it back, still warm, but much drier. Waste heat from dehumidification was recovered and used to heat water in the pool tank. Fig- ure 1 on page 21 shows a section through the pool, service space, and parking garage. The client had a persistent and ongoing problem where, every winter, icicles would form on parts of the ceiling tiles and, with the arrival of spring, soaked ceiling tiles would fall to the garage floor. The tiles were replaced, and this happened again. Nobody understood why this was happening. The issue was the space was confused; it wasn’t really outside nor was it inside. MISSING AND CONFUSED BARRIERS It has been written that good building en- velope design requires continuous lines on a section through the exterior wall, with those lines representing each key layer of the envel- ope. As shown in Figure 1, these lines are: a thermal barrier preventing heat from moving from one side to another; an air barrier sep- arating inside and outside air; and a vapour barrier preventing water vapour (found in air) from moving from one side to another. In cold climates, the vapour barrier is typical- ly on the warm side of the wall. In this confused space, the lines were missing, discontinuous, or in the wrong spot. Although the concrete structure formed a good air and vapour barrier, it did not enclose the service space. The surface of the ceiling tiles in the garage were really the building envelope. They had fiberglass batt insulation that acted as a thermal barrier, they weren’t really an air barrier (owing to their numerous unsealed joints), and they acted as a vapour barrier—but on the wrong side of the wall. Ductwork ran through the service space, drawing warm, humid air from the pool room and sending it to the dehumidifier in the parking garage. The humid air from the pool leaked out of joints in the ductwork into the service space. At about 28oC, this humid air had a dewpoint of about 16oC. Any sur- face below 16oC that came into contact with this air would form condensation. The ceiling tiles in this space were ex- posed to the cold parking garage, which was often below freezing with the garage over- head door nearby. Condensation, frost, and then icicles formed on the tiles. The vinyl facing of the tiles trapped moisture and frost within the tiles themselves. The service space was confused because there was no way to keep this humid air sep- arate from the cold, dry parking garage. The air barrier and vapour barrier were both in the wrong location. DUCTWORK OUTSIDE THE CONDITIONED SPACE Much has been written about ductwork placement inside buildings. In the humid cli- mates of the southern U.S. states, it is com- mon to place ductwork out of the way, in hot attics that have a very high temperature and a very high dewpoint. In turn, this causes con- densation when the air conditioner operates. This was the same problem, but in re- verse. Running ductwork carrying warm air with a high dewpoint through a cold, dry space causes the same problem as running cold, dry air through a warm and humid space. Who would’ve thought? AIR BARRIER POSITIONING AND CONTINUITY Even those unversed in building science principles understand the importance of keeping the warm air inside—or sometimes, the hot air outside. A continuous air barrier, that line in the sections, is critical for a build- ing envelope to function correctly. More subtle is the location of the air bar- rier, particularly in confused spaces that are neither inside nor outside. In the case study, the air barrier didn’t enclose that warm duct- work within the building envelope. SELECTING MATERIAL FOR THE VAPOUR BARRIER ON THE WARM SIDE OF WALL Those same people who are unversed in building science have learned through home improvement shows the importance of FEATURE n n n By Daniel Martis, P.Eng., LEED® AP, Principal, Project Manager, Morrison Hershfield Ltd.Pushing the Envelope Canada 21 putting up that clear, plastic sheet, or vapour barrier, inside a wall before finishing. Not everybody understands why—just that you have to do it. In cold climates, warm, indoor air often has more water vapour in it than outdoor air does. The clear, plastic vapour barrier keeps that warm air inside, where it belongs. The rule follows that vapour barriers should be on the warm side of the assembly. More subtle is the fact that other materi- als can unintentionally act as a vapour bar- rier. Many materials beyond polyethylene are great vapour barriers. Most famous is vinyl wallpaper used on the interior side of walls in warm climates. In the case study, the vinyl facing of the ceiling tiles was a very good vapour barrier— but it was on the cold side of the wall. This captured water vapour migrating outward into the dry parking garage, forming icicles. USING XPS AS A VAPOUR RETARDER In the theme of using alternate materi- als, extruded polystyrene insulation (XPS) is a great vapour retarder once it’s more than about one inch thick. It also serves double duty as an insulating material. Being aware of all of the physical charac- teristics of a material was useful in develop- ing this repair strategy. MANAGING RELATIVE HUMIDITY FOR A VENTILATION SYSTEM AND ENTHALPY CONTROL Some building scientists might be famil- iar with the adage, “build tight and ventilate right.” It is easy to over- or under-ventilate an indoor space. The tricky part comes with using the correct amount of ventilation. We were concerned for ventilation of the confused space, particularly with air leakage from the ductwork. In the absence of venti- lation, the relative humidity in the confused space might still end up being too high at times. However, during the summer in a cold climate, ventilation becomes less important, as the outdoor air and the air in the pool space have almost the same temperature and dewpoint. The question then became, “How do we ventilate this properly?” The solution was using enthalpy control to ventilate only when the indoor and outdoor conditions required it. Mechanical engineers are, no doubt, familiar with enthalpy of air, while civil engineers may have tried to put it out of their mind. Enthalpy controllers are used to monitor and command a “free cooling” mode in roof- top HVAC units. When outdoor air has the right enthalpy (being the right combination of temperature and humidity), it can provide the cooling needed for an indoor space. In the cold climate of the case study, the enthalpy controller demanded ventilation for the service space only during the winter, when exhausting humid air. Making it up with cool, dry air from the parking garage helps to keep the relative humidity at a rea- sonable level. THE SOLUTION The solution for this confused space involved several things. First, joints in the ductwork were air-sealed to keep most of the humid air where it belonged, though some would still leak. We also constructed a wall inside the service space to better enclose the ductwork. The new wall used XPS insulation as an air barrier, vapour retarder, and ther- mal barrier to keep the ductwork separate from the cold ceiling tiles of the parking gar- age. Figure 2 (above) shows the new wall. THE TAKEAWAY Confused spaces present themselves when the separation between indoors and outdoors gets blurred. Often, this happens when there is a big difference between the indoor and outdoor temperature and the dewpoint for most of the year. Attics, crawl spaces, and service spaces are great locations to run building services, but in most climates, these services should remain inside of the building envelope. These spaces need a complete building envelope to make a clear distinction between indoors and outdoors. The greater the differ- ence in temperature and humidity, the great- er the risk of something going wrong. This is why swimming pools in cold climates can present the same challenge as hockey rinks in humid climates. Working with your building envelope consultant is key to ensuring these spaces work as intended. n Daniel Martis, P.Eng., LEED® AP, is a principal and project manager at Morrison Hershfield Ltd. He has 15 years of broad ex- perience in building envelope and concrete res- toration. His focus is on facilities assessment, management and capital planning, and build- ing repair and restoration, including repairs to structural concrete. n n n FEATURE Figure 2. The location of the new wall and ventilation equipment. Figure 1. A section showing the pool, dehumidifier, and suspending ceiling in a parking garage. Pushing the Envelope Canada 23 The serious consequences of climate change have led to a global need for a decrease in energy use and CO 2 emis- sions. In Canada, buildings account for ap- proximately 30 per cent of secondary energy use and 25 per cent of CO 2 emissions, mak- ing the building sector an important target for decreasing the impact of climate change.1 Canada has been a leader in low-energy building design since the 1970s; however, the exploration and implementation of these designs has lagged significantly. With the in- creasing need for buildings to perform better, research and application of innovative, low- energy building designs is a requirement of the modern day. The nested thermal envelope design (NTED) is a modern building design ap- proach developed by Dr. Kim Pressnail of the University of Toronto and Dr. Russell Richman of Ryerson University. The ap- proach builds upon early passive design principles and develops multiple double-en- velope building designs first pioneered in the 1970s.2,3 The NTED system consists of two thermal zones–the perimeter and core–acting independently in controlling heat, moisture, and air movement within a building. The core serves as the main living space, which is operated at desired living conditions year-round, and the perimeter is a second- ary living space that may be used and con- ditioned only when needed. Both zones can be operated at a common set-point temper- ature, called the standard mode. However, when a homeowner wants to maximize energy savings, the house can be operated in low-energy mode, in which only the core areas are occupied and conditioned. This mode reduces energy use by decreasing the thermal gradients across each envelope and the conditioned area of the house. One problem often faced by designers of low-energy buildings is controlling and using solar gains. To do this, the NTED sys- tem uses an inter-zonal heat pump, which transfers solar heat gains from the perimeter to the core during the winter and transfers heat from the core to the perimeter in the summer. This allows perimeter thermal con- ditions to be varied and energy recovered as needed. The NTED new-build is a low-energy residential home design developed by the lead author to model the energy perform- ance of a fully implemented NTED system in Toronto.4 It includes standard architectur- al features for a low-rise residential home, divided into core and perimeter spaces. The perimeter spaces consist of two areas: an air space and living space. The 150 mm ‘air space’ surrounding the north, east, and west walls of the main and second floor of the house (shown in Figure1, below) are used for service routing and to allow airflow by natur- al convection throughout the home. The basement level is entirely a per- imeter zone, where the mechanical equip- ment and storage space is located. The per- imeter living space on the main and second floors has a heavily glazed, south-facing area that collects solar heat. Where glazing is located along the air space area, there are two layers of windows provided: one set for the perimeter envelope and one for the core envelope. To limit carbon emis- sions due to energy use, the NTED design uses only electricity as the energy source for heating since, in Ontario, heating with electricity has a lower emission factor than heating with natural gas. Dividing a home into core and perimeter areas leads to the question, “What perimeter air temperature will result in the minimum heating energy use?” Minimum heating energy use occurs when heating energy is only supplied to the core and no additional heating energy is supplied to the perimeter. So, this minimum energy use will corres- pond to a perimeter operating temperature that will vary as the outdoor air temperature varies. The most efficient perimeter operating temperature is a function of the outdoor temperature and it is a function of the rela- tive overall thermal resistance and air tight- ness of the core and perimeter envelope. Therefore, each NTED house has a unique optimum perimeter operating temperature for a given outdoor air temperature based on its envelope. To remove weather as a vari- able, it is useful to define a quantity, which we will call the “operating ratio” (OR). The OR Analyzing the Energy Performance of a Nested Thermal Envelope Design New-Build Home n n n FEATURE By Anna Farbis, B.A.Sc., Project Coordinator, Pretium Engineering Inc. & Dr. Kim Pressnail, Associate Professor of Civil & Mineral Engineering, University of Toronto Figure 1. Floor plans of the NTED new-build.24 Fall 2019 • Ontario Building Envelope Council normalizes for the effects of weather and can be defined as follows in Equation 1: Where: • TC is the air temperature of the core; • TP is the air temperature of the perim- eter; and • TO is the outside air temperature. It’s worth noting the formula for the OR bears a striking resemblance to the temper- ature index often used to describe window performance. That’s because the same con- cept that normalizes temperature differences for windows has been applied to a nested thermal envelope home. The perimeter air temperature is analogous to the surface tem- perature of the glass. The OR is a useful tool for deciding when there is excess heat in the perimeter. If there are excess solar gains, the perimeter can be cooled by means of an inter-zonal heat pump that can be used to pump excess solar heat into the core. This can be an efficient means of solar control, particularly since heat pumps operate most efficiently when air temperature differences are small. We can determine the OR for the NTED new-build. Recall that minimum heating energy use occurs when heat energy is only supplied to the core. If we neglect air leakage, then, at steady state, the heat flowing through the core envelope to the perimeter is equal to the heat flowing through the perimeter envelope to the outside. This is described by Equation 2: U CAC (T C – T P) = U PAP (T P – T O) Where: • TC, TP are the air temperature of the core and the perimeter, respectively; • TO is the outside air temperature; • UC, Up is the overall heat transmission coefficient for the core envelope and per- imeter envelope, respectively; and • AC, AP are the overall areas of the core envelope and perimeter envelope, re- spectively. Equation 2 can be rearranged to isolate the dependent variable, TP, substituted in Equation 1, and simplified to create Equa- tion 3, which defines the OR as a function of the overall heat transmission coefficients of the core and the perimeter: OR = U CAC U CAC + U PAP We can now find the sum of the prod- ucts of thermal conductance values and re- spective areas for each component in both the core and perimeter. These values are FEATURE n n n ZoneComponentUA (W/K)UA (W/K) Perimeter Perimeter Wall53.32 91.57 Basement Wall17.65 Basement Floor10.54 Perimeter Roof10.06 Core Core Wall41.96 67.26Core Floor9.88 Core Ceiling15.43 Table 1. Calculation of the overall thermal conductance for perimeter and core zones. Operating Ratio (OR) =T P – T O T C – T OPushing the Envelope Canada 25 shown in Table 1 (on the previous page) for the NTED home. The OR for the new-build can now be found by substituting the values shown in Table 1 into Equation 3. Using Equation 3 and the values provid- ed in Table 1, the NTED home was found to have an OR of 0.42. “Mathemagic” aside, this means that to minimize heating energy use, the perimeter should be operated so that approximately 40 per cent of the air temper- ature drop between the core and the outside occurs across the perimeter envelope. How- ever, there is a limit to how low the perimeter temperature should go. To reduce the risk of damage due to freezing materials, including plumbing pipes in the perimeter, a lower lim- it of 5oC was applied. In cases where the OR could lead to perimeter temperatures of low- er than 5oC, the set point temperature would be governed by this lower limit. HOT2000 Energy Modelling software was used to model the energy performance of the NTED new-build to determine the effectiveness of its design. This model fo- cused on heating energy usage, since this is the greatest energy demand for a house in Toronto. The Low-Energy Mode could not be modelled directly using HOT2000, since the software only allows one conditioned zone. There was also no way of simulating an inter-zonal heat pump. So, to model the NTED new-build using HOT2000, a few work-arounds had to be developed. The first step was determining the energy needed to heat the core zone only, without any benefit of solar heat gains. To do this, the base- line model was developed, which closely resem- bled the properties of the NTED new-build, excluding windows. This low-energy model assumed that, during the heating season, the perimeter was consistently kept at a setpoint temperature determined by the OR. As a re- sult, only the perimeter building envelope was modelled, and the core / perimeter interface was assumed to be entirely adiabatic. The second step was determining the energy needed to heat the core zone only, with the benefit of solar heat gains in the per- imeter. This was done by including the glaz- ing area, at the specifications of the original design, within the baseline model to form the solar gain model. Using an assumed core air temperature of 21oC in the winter and 24oC in the summer, along with monthly average outdoor tem- peratures in Toronto, the average perimeter set-point air temperature was calculated for each month. Both models were run 12 times with each monthly perimeter temperature, and the results were added for each model to determine an annual heating energy use with and without solar gains. These values were subtracted to deter- mine the amount of heat energy generated through solar gains in the perimeter that could be transferred to the core. As a result, the perimeter is expected to stay at the tem- peratures defined by the OR, while the core benefits from the additional heating energy provided by the perimeter glazing area. Figure 3 (above) summarizes the energy modelling results for the NTED new-build, compared to the general requirements of the Passive House Standard. The results of the standard and low- energy modes provide the upper and low- er bounds of heating energy performance for the NTED house. It’s worth noting that under low-energy mode, the perimeter may often become a thermally uncomfortable space during winter and summer months, so the usable floor area should only encompass the core floor area for direct comparison to the Passive House standard. Under these circumstances, the space heating demand of the NTED new-build is 6.42 kWh/m2 annu- ally. This is less than half of the requirement to meet the Passive House Standard space heating demand (15 kWh/m2), achieved with comparable amounts of insulation. The objective of the NTED new build de- sign and energy model was to continue explor- ation into innovative design and construction methods for low-energy, single-family homes in cold climates. Through the concept of the operating ratio and an innovative modelling methodology, the energy performance of the NTED new-build, and consequently all NTED homes, could be determined. The hope is that the exceptional energy perform- ance of this design will lead to further explor- ation into the NTED concept and the reduc- tion in the construction of energy inefficient homes that are less durable and place a great- er burden on the environment. n Anna Farbis works as a project coordinator at Pretium Engineering Inc. She received her bachelor of applied science in engineering sci- ence in 2019 at the University of Toronto. She specialized in infrastructure engineering and completed an undergraduate thesis in low-en- ergy building design. Kim Pressnail is an associate professor of civil and mineral engineering at the University of Toronto. He teaches and researches building science at the University of Toronto. n n n FEATURE REFERENCES 1. Environment and Climate Change Canada, Canada’s Emission Trends 2014, Environ- ment Canada, June 2017. [Online]. 2. M. E. Rumeo, Evaluating the Field Per- formance of a Thermally-Retrofitted Historic Masonry Home Using a Nested Thermal Envelope Design, Master of Applied Science, University of Toronto, Toronto, ON, 2019. 3. K. D. Pressnail, R. Richman. A. M. Kirsch, An Innovative Approach to Low-Energy Building Performance Using Nested Thermal Envelopes, 12th Canadian Conference on Building Science and Technology, Montréal, Québec, Canada, 2009, vol. 2, pp. 393–404. 4. A.W. Farbis, The Gemini House New-Build: The Design and Energy Model of a Sin- gle-Family Home Using a Nested Thermal Envelope Design, Bachelor of Applied Science in Engineering Science, University of Toronto, Toronto, ON, 2019. Figure 3. Insulation levels required for average Passive House home vs. NTED home. Figure 2. Heating energy use intensity (kWh/m2) for Passive House home versus NTED home.26 Fall 2019 • Ontario Building Envelope Council The idea that high-rise multi-unit resi- dential buildings (MURBs) should be compartmentalized to minimize the impacts of stack effect and be equipped with balanced in-suite ventilation systems is not a new concept. Local building science literati have been talking about this for dec- ades, from the Canada Mortgage & Housing Corporation (CMHC) to the late venerable Gus Handegord and his disciples. That’s all well and good, but why would you do that if it costs more? As it turns out, you wouldn’t. At least not until recently and, even then, only in rare cases when there are ambitious indoor environmental quality goals. Or, if you happen to be designing a garden variety apartment building in Scandinavia for some reason. The existing stock of high-rise MURBs in Canada’s urban centres is substantial, with its own building boom generation entering re- tirement age, and you won’t find many—or any—that were built this way. Now, there’s a growing need to renew this building stock and a mounting interest in retrofitting the envelopes to improve overall performance and refresh the appearance. Because the en- velopes of these buildings are typically poorly insulated and leaky, this makes sense; you need an efficient envelope to reduce heat loss and infiltration. Unfortunately, what usually gets over- looked in major MURB retrofits is the venti- lation system, which is often highly ineffect- ive and can be made worse by an envelope retrofit. It might seem counterintuitive, but perhaps we should be compartmentalizing these buildings and decentralizing the venti- lation system before we retrofit the envelope, or at least do them simultaneously. There are reasons behind this silly talk. Most high-rise MURBs use a pressurized corridor ventilation strategy. These systems use a rooftop make-up air unit (MAU) to blow air down a central trunk duct and into the corridors of each floor in the hopes it will pass through the door undercuts, ventilating the suites before continuing outside through the bathroom exhaust ducts and other cracks and openings in the envelope. This works quite well on paper, and it can work in real- ity, as long as: • The system is still balanced and operating as when it was originally commissioned; • The occupants haven’t sealed around their front doors for some reason and don’t open their windows or balcony doors; • The heating system isn’t on and causing a stack effect; and • It’s not windy outside. It’s a little finicky, sometimes. Convin- cing air to evenly distribute itself among the suites is like herding ghosts. If someone opens a window, the air tends to go through that suite, bypassing the others on the floor. Or, it might travel up the elevator shaft, skipping the suites altogether if that’s easier. This ventilation strategy relies on a positive pressure differential from the corridor to adjacent suites and from the suites to out- side to maintain the desired airflows. The air pressure distribution in the building is con- tinually disturbed by factors such as the stack effect, elevator operation, window operation, and wind pressures on the building’s exterior. The result is a highly variable and unpredict- able fresh air delivery rate to individual suites under constantly changing conditions, even during normal building operation, which negatively impacts indoor air quality. The dynamic pressure fields from wind and the stack effect can overpower the mechanical ventilation system, altering or even reversing airflow to suites. MAUs are commonly over- sized to overcome these confounding factors. Air will always take the path of least re- sistance, there may just be more of it going where it’s not designed to. In the heating season, the stack effect can draw polluted air up from the parking garage into suites on the lower floors. If someone decides to take up the newly legal practice of cannabis horti- culture (except for those in Manitoba and Quebec, where it’s not legal), the entire building above them is going to smell it. Not to mention, if they’re combusting it. If each suite is individually sub-metered for heating energy, tenants on the lower floors inevitably also pay to heat the upper floors. As warm air rises and pushes out the top half of the building, it’s replaced by cold air drawn into the lower suites, causing them to crank their heat while upper floors shut theirs off, or even open windows in an FEATURE n n n By Matt Carlsson, M.A.Sc., P.Eng., C.P.H.D, Building Science Consultant, Morrison Hershfield Ltd. A Retrospective Retrofit Perspective for Aging Multi-Unit Residential Buildings Stack Effect, GHGs, & Cannabis Smoke:Pushing the Envelope Canada 27 attempt to combat overheating—a phenom- enon building scientists refer to as “tragic irony.” Tenants on upper floors have little incen- tive to close their windows in the winter, as air is constantly flowing from the inside out, while lower floors are drafty. Since there is typically no central return duct, there is no opportunity for heat recovery; a pretty ineffi- cient system. It’s a very inexpensive solution, and elegant in its simplicity. Like a lemon bat- tery. Despite decades of evidence and plenty of research showing them to be ineffective, they continue to prevail as the dominant ventilation strategy for high-rise MURBs. VENTILATION DISTRIBUTION EFFECTIVENESS AND ENVELOPE RETROFITS An envelope retrofit that improves overall airtightness can have the unintended conse- quence of amplifying the deficiencies of pres- surized corridor ventilation systems. Because bathroom exhaust fans are operated inter- mittently—whereas the central ventilation system is usually a constant flow rate—the air will find other ways to exit the building. A 2013 CMHC study examining the effect of envelope retrofits on six MURBs showed that average air leakage rates through the ex- terior envelope were reduced by 31 per cent. This is good, of course, but if the envelope is made more airtight without a change in the ventilation strategy, the desired decrease in airflow through the envelope can also mean a corresponding and undesirable decrease in ventilation air reaching suites. Although air leakage can be a significant source of energy loss, envelope airtightness improvements without a change in ventilation strategy can degrade indoor air quality and encourage occupants to leave their windows open more, undermining the airtightness effort. CASE IN POINT Comprehensive airflow measurements and tracer gas testing following an exten- sive envelope retrofit of a 13-storey, 37- unit, 5,176-metre-squared (gross floor area) MURB in Vancouver found as little as eight per cent of ventilation air was actually reach- ing suites, with the remaining lost mostly to elevator shafts, stairwells, and duct leakage. The energy used to heat the ventilation air accounted for over half the overall heating energy for the building; clearly, not an ef- ficient use of resources. This building was used as a case study to build two calibrated EnergyPlus baseline models using the meas- ured performance characteristics of the ori- ginal 1986 construction and the 2012 envel- ope retrofit (ENCL). The models were used to simulate a compartmentalization and in- suite ventilation system (C+ISV) retrofit and investigate the potential impact on energy use and greenhouse gas (GHG) emissions. Isolating the floors from one another through air sealing helps reduce the stack effect and issues associated with it. Sum- moning a conceptualization made famous by the aforementioned building science scholar, it’s like turning the building into 13 single-storey buildings stacked on top of each other. Now, suite ambient pressures can equalize with outside atmospheric pres- sure, reducing uncontrolled airflow through the envelope. With a leaky envelope in windy conditions, air pressure in the suites should still equalize quickly with the exterior ambient pressure, even though it might vary between the windward and leeward sides of the building. Of course, you can’t compart- mentalize the elevator shaft, so sealing the suite-to-corridor boundaries helps isolate the stack effect to the building’s core. Figure 1 (below) illustrates this concept. The central ventilation system flow rate could then be reduced significantly to the level required to serve only common corri- dors, resulting in a corresponding decrease in natural gas used to condition the outside air. Fresh air would be provided to each suite through a dedicated heat recovery ventila- tor (HRV). The HRV’s balanced intake and exhaust flows help prevent pressurization or depressurization of the suite and reduce uncontrolled air leakage. A decentralized ventilation system also enables demand-con- trol, so individual suites are not ventilated unnecessarily while unoccupied. DISCUSSION Both retrofit measures examined offer energy and GHG reductions through the de- crease in space heating energy demand com- pared to the original building construction. Increasing the thermal performance and airtightness of the building envelope through a complete envelope retrofit reduces air infil- tration and conductive losses through outside walls, reducing overall space heating energy. Since mechanical ventilation rates aren’t ad- justed in this scenario, heating energy savings are realized solely by the electric baseboard heaters in each suite. Since the electrical grid in this case is largely supplied by low-carbon resources, the reduction in electricity use for heating through an envelope retrofit alone has very little impact on the building’s overall GHG emissions. Cannabis Smoke: Figure 1. A schematic illustrating the impact on pressure distribution and stack-induced airflows of the air-sealing retrofit. Figure 2. Heating energy and greenhouse gas emissions reductions by retrofit strategy. n n n FEATURE28 Fall 2019 • Ontario Building Envelope Council In the proposed compartmentalization and in-suite HRV retrofit scenario, energy savings predominantly result from the addi- tion of heat recovery for mechanical ventila- tion and reduced infiltration from the stack effect. Since ventilation air is supplied directly to the suites, the central ventilation rate from the MAU can be significantly reduced to what is required for just corridors. Although over- all space heating energy savings are less with the proposed retrofit than with the envelope retrofit, GHG emissions reductions are great- er since the central MAU supply air is heated by burning natural gas. Figure 2, on the pre- vious page, summarizes the simulated heating energy and associated GHG emissions reduc- tions of each retrofit strategy. The ENCL retrofit, which mitigated conductive heat loss through the building envelope, resulted in the greatest reduction in space heating energy, decreasing by 55 per cent (617 MWh or 119 ekWh/m2). The C+ISV retrofit, which eliminated most of the natural gas combustion associated with conditioning ventilation air, resulted in the greatest GHG emissions savings, with a reduction of 70 per cent (43.9 t CO 2e, or 8.5 kg CO 2e/m 2 ). The greatest savings are found with both retrofit measures applied together, resulting in a space heating energy reduction of 78 per cent (869 MWh or 168 ekWh/m2), and lower associated GHG emissions by 83 per cent (52.1 t CO 2e, or 10.1 kg CO 2e/m 2 ). COLLATERAL BENEFITS Unrelated to energy or carbon savings, but of equal or greater importance, is the potential for improved indoor air quality as a result of the proposed retrofit. Compart- mentalization of the suites mitigates the transfer of airborne contaminants among suites, and the addition of dedicated HRVs allows for fresh air to be provided effectively to the suites at the full recommended design rate, which is difficult to achieve in reality through corridor pressurization. In addition to improved indoor air quality, the proposed C+ISV retrofit allows for demand control of ventilation rates at the individual suite level. Ventilation can be reduced or turned off dur- ing unoccupied hours of the day and / or days of the year, reducing unnecessary heat loss and fan energy. Reducing the stack effect also results in improved thermal resilience of high-rise MURBs in the event of power loss in heating and cooling seasons. During a power outage, a typical high-rise can become quickly un- inhabitable from heat loss, cooling capacity, and the rapid loss of conditioned air from the building due to the stack effect. Mitigating this effect through suite compartmentaliza- tion can reduce uncontrolled air flow from the building, allowing occupants to remain in place longer before interior temperatures force evacuation. Other benefits include re- duced sound transmission, improved odour control, and better smoke and fire control. CONCLUSION The impact of the proposed compart- mentalization and in-suite ventilation retrofit, if applied on its own to a high-rise MURB with a leaky and thermally ineffi- cient envelope, can reduce energy con- sumption by reducing infiltration caused by wind and the stack effect and positively impact mechanical ventilation distribution effectiveness, improving indoor air quality for residents. Because building envelope airtightness improvements can negatively impact ventilation air distribution to suites in buildings with pressurized corridor FEATURE n n nPushing the Envelope Canada 29 ventilation systems, the proposed retrofit should be applied in combination with, or before, any major envelope retrofit. Nationally, residential buildings ac- counted for 15 per cent of Canada’s overall GHG emissions in 2013, with space heating energy making up 64 per cent of the total residential sector output. The GHG emis- sions factor for electricity in British Columbia is relatively low, at 25 g CO 2e/kWh compared to the 2013 Canadian national average of 150 g CO 2e/kWh, so the benefits of the proposed retrofit should be more significant in most other provinces. The GHG reduction potential would also be amplified in the other provinces, as their climates are generally much colder than British Columbia’s, resulting in higher heating energy demand and greater stack effect pressures. Not to mention, a 13-stor- ey building barely qualifies as a high-rise these days and, the taller the building, the greater the stack effect. The proposed retrofit is an opportunity to contribute to municipal, provincial, and national GHG emissions reduction objectives across Can- ada, particularly in regions like the Great- er Toronto Area, with its cold winters, hot summers, abundance of tall MURBs, and relatively low-carbon grid electricity. n Matt Carlsson, M.A.Sc., P.Eng., C.P.H.D, is a building science consultant with Morrison Hershfield Ltd. and is a professional mechani- cal engineer in Ontario. He is a certified Passive House consultant and holds a master’s degree in building science. Carlsson’s professional experience includes mechanical commission- ing for data centres, residential HVAC system design, energy modelling, hygrothermal simula- tion, and carbon-neutral and deep energy retro- fit feasibility studies. n n n FEATURE REFERENCES 1. Canada Mortgage & Housing Corpor- ation, Ventilation Systems for Multi-unit Residential Buildings - Performance Re- quirements and Alternative Approach- es, February 2003 2. Carlsson, M.; Touchie, M.; & Richman R., Investigating the Potential Impact of a Compartmentalization and Ventilation System Retrofit Strategy on Energy Use in High-Rise Residential Buildings, Journal of Energy and Buildings, Volume 199, September 2019 3. Environment Canada (2015), National Inventory Report 1990-2013. Greenhouse Gas Sources and Sinks in Canada: Part 3, 1–85, http://doi.org/ISSN: 1719-0487 4. Handegord, G.O., A New Approach to Ventilation of High-Rise Apartments, Proceedings of the Eighth Conference on Building Science & Technology, Ontario Building Envelope Council, Toronto, Ontario, February 2001 5. NRCan (2017), Comprehensive Energy Use Database, Retrieved from http:// oee.nrcan.gc.ca/corporate/statistics/ neud/dpa/menus/trends/comprehen- sive_tables/list.cfm 6. Ricketts L. & Straube J., Corridor Pres- surization: It’s Out of Control, Pushing the Envelope Canada, Fall 2014 7. Wray, C.; Theaker, I.; & Moffatt, P., Field Testing to Characterize Suite Venti- lation in Recently Constructed Mid- and High-Rise Residential Buildings, CMHC Project Report. 1998Next >