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Ventilation options in high-rise condos
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June, 2009

By Gord Cook

Developers, architects, engineers and operators of high-rise residential condominiums have been rethinking the conventional building air management systems. The goal is to optimize building energy costs and improve occupant satisfaction with respect to noise and odour transmission between suites and between common hallways and suites.

Since the mid-1960s, multi-unit residential buildings have been equipped with corridor ventilation systems and in-suite, or central, bathroom and kitchen exhaust to meet ventilation needs. The corridor air systems (typically roof mounted) were originally included to provide some measure of smoke control in hallways in the event of fire. They were designed to provide make-up air for in-suite exhaust appliances such as bathroom fans, range hoods and, more recently, clothes dryers. To accommodate this flow of air from hallway to suites, suite entry doors were undercut. This continuous pressurization of hallways also indirectly provided fresh air to suites and helped control odour transmission between suites.		  

Research by Canada Mortgage and Housing Corporation and others suggest that this conventional corridor ventilation strategy is neither effective nor efficient. These studies concluded that over 30 per cent of the corridor ventilation air never makes it into individual suites. This waste of ventilated air is very important, since ventilation and air leakage accounts for up to 50 per cent of the heating and cooling energy use in high-rise buildings.

The research also found that exterior building envelopes have gotten much tighter as the result of efforts to minimize water intrusion and individual suites are much tighter because of improvements in fire and smoke control measures. In recent years the addition of individual suite clothes dryers and larger range hoods has meant a greater depressurization of suites and a requirement for larger make-up air capacities. As well, occupants have increasing expectations for noise, odour, humidity and temperature control.

In light of this research, the most progressive and energy conscious designers and building owners are implementing two complimentary strategies. The first is to compartmentalize suites to make them even tighter. The second is modifying fresh air ventilation strategies to ensure fresh air is delivered directly to suites and incorporating energy recovery into the system design.
Weather-stripping of suite entry doors and enhancing the caulking and foaming that is already done for smoke and water intrusion is all that is needed to compartmentalize suites. This strategy can be employed in new and old buildings but is undoubtedly most effective in new building design. It is important to note that the compartmentalization must be done in conjunction with ventilation changes – it would be inappropriate (and in many cases contravene local codes or standards) to make suites tighter without adjusting the ventilation components.

The ventilation changes are significant and there are at least two strategies commonly used. The first is to use central (whole building) Energy Recovery Ventilation systems (ERVs) that pick up exhaust from suite washrooms through large central ducts and supply fresh, conditioned air directly to suites or at least to hallways. While some older buildings do have central exhaust shafts where exhaust fans could be removed and replaced with energy recovery units, this strategy is most applicable in new buildings.

 
The second strategy is to use individual suite ERVs. These are small stand alone units located in a closet or above a ceiling space in each suite. They exhaust air from the washrooms and potentially the kitchen and draw in fresh ventilated air from outside to be distributed throughout. The waste exhaust air energy is used to preheat or pre-cool the fresh air. Again, incorporating these units into new building designs would be most cost effective, but this strategy can be employed in existing building as well with the advent of new smaller, energy recovery systems designed specifically for high-rise buildings.
 
Of course, there are a number of design considerations for each of these strategies that can be used to optimize both installation and operating costs. Two of the most important issues are the ventilation rate and the control of suite and hallway pressures.
 
Canadian codes and standards make it clear that the ventilation rates for individual suites in high-rise buildings should match those described in residential sections of codes rather than be designed at commercial occupancy rates. This in itself provides an excellent opportunity for costs savings. Exhaust rates for residential bathrooms, for example, are at least half that used in commercial exhaust design. Applying proper, lower rates will allow engineers to dramatically downsize make-up air systems and heating and cooling capacities.
 
Due to both natural and mechanical forces, building pressures in high-rise applications vary constantly due to stack effects in winter (warm air rising, cold air falling), wind and the operation of various exhaust and supply air fans. The complicated pressure differences between suites throughout a building caused by stack effect and exhaust fan operation can be the equivalent of a 60 kph wind and have many implications on operation and occupant satisfaction. For example, exhaust flow rate from dryers and range hoods varies from floor to floor and these devices often don’t work to their design capacity. As well, pressure differences between suites may result in unusual odour flow patterns.
 
Managing the effects of these pressures is much easier to handle in tighter buildings. It reduces the amount of air required to manage pressures, it avoids unwanted air leakage through building envelopes and is the most significant energy saving strategy in most buildings. Tight buildings with balanced ventilation systems should be the goal of all designers and building owners. Ideally, individual suites would be very tight, with weather-stripped entry doors and a well detailed envelope air barrier. Then each suite could have a balanced ventilation supply and exhaust system.
 
There are great opportunities for new ventilation strategies in high-rise residential buildings. Designers and building owners can benefit from the years of research that have been done. Learning from important industry research allows for more cost effective, energy efficient, healthy buildings that help meet the ever increasing expectations of condominium owners.
 		  
 
 
 
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