Options for mechanical ventilation systems

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Options for mechanical ventilation systems


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air quality mechanical ventilation systems cmhc

September 28, 2011

By Paula Gasparro

In the September issue of CondoBusiness, we told you about how proper mechanical ventilation systems can enhance indoor air quality. Here are some system options that you can consider for your condo building if you are looking at a new development or retrofitting.

Some System Options:

Central Supply and Exhaust

Air is supplied to rooms in the suite from a central supply system directly ducted from the central supply. Air is exhausted from each suite with a central exhaust system. Air should be supplied directly to all rooms without exhaust capacity.

Advantages
• Can provide a minimum continuous airflow to all suites.
• Reduces suite depressurisation and minimises envelope air leakage.
• Heat recovery to pre-heat supply air can be provided from a central location.
• Can be supplemented with individual suite exhaust or a booster fan in a central shaft.
• Single point of maintenance.
• No supply air intake required for each apartment.
• Building operators can control ventilation rates and ensure that the building is properly ventilated.
• Less space required in apartments than for ensuite systems.

Disadvantages
• Supply air transferred from corridors (if not directly ducted) may not meet fire safety requirements.
• Supply air inlets may be sealed by occupants to reduce noise and drafts (if not directly ducted).
• Increased building stack effect due to increased coupling of floors.
• Loss of occupant control.
• Larger common space commitment (ie. mechanical rooms).
• Greater smoke, odour, noise and pest transfer is possible.

Individual Unit Exhaust - Central Supply Air

Dwelling units operate under continuous exhaust from individual dwelling unit systems. Fresh air is supplied through a central supply system - directly ducted from the central supply.

Advantages
• Can provide a minimum continuous airflow to all suites.
• Greater compartmentalisation of dwelling units.
• Exhaust rate controllable by occupants.
• No supply air intake required for each apartment.

Disadvantages
• No heat recovery of exhaust air possible.
• Difficult to balance.
• Loss of control by condo corporation
• Could pressurize the building and cause envelope problems.
• Supply air transferred from corridors (if not directly ducted) may not meet fire safety requirements.
• Supply air inlets may be sealed by occupants to reduce noise and drafts (if not directly ducted).

Individual Suite Balanced System

Air is supplied and exhausted from each dwelling unit with an individual unit heat recovery ventilation system (HRV), which recovers heat (or cold) from exhaust air flow to temper the incoming airflow.

Advantages

• Can provide a minimum continuous airflow to all suites.
• Heat recovery of exhaust air reduces energy consumption.
• Allows compartmentalisation of individual suite.
• Balanced air pressure in suites reduces airflow though exterior walls, vertical walls, vertical shafts, and from other suites and common areas.
• Easy to balance.
• Increased occupant control.
• Usage is billable to occupants.

Disadvantages

• Capital cost of Unit HRV.
• Requires balancing.
• Requires separate system for corridors.
• Many points of maintenance.
• Large number of motors consuming energy.

Retrofit opportunities

Ventilation systems in existing buildings often perform poorly compared to their original specifications. Retrofit opportunities to improve performance include:

1 Balancing airflows – Corridor pressurisation and central exhaust systems should be rebalanced to ensure that air supplies and exhaust rates are meeting their original specifications and are properly distributed throughout the building.

2 Installing ventilation supply to individual rooms –Central corridor pressurisation systems can be modified to supply ventilation air directly to individual suites. The only time that such a retrofit is possible is during major renovation.

3 HRV units can be installed in exterior walls of individual suites during renovation of each suite.

Paula Gasparro is the Manager, Business Development , Multi-Unit Mortgage Insurance at the CMHC. To take advantage of CMHC’s research on the Healthy High-Rise, or Mortgage Loan Insurance, contact her at 416-250-2731 or via e-mail at pgasparr@cmhc.ca.

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