Tuesday, May 10, 2011

Ventilation Control Systems

Today's energy efficient homes do a great job of keeping conditioned air in. But, the downside of a well air sealed and insulated home is that reduced stale air exhaust and air exchange with the outside can result in poor indoor air quality which may lead to occupant health and structure durability problems. Even air systems that are designed with a fresh air intake do not provide ventilation or exhaust when they are not operating.
Economical and affordable ventilation controls are ideal for use with exhaust or supply fans, air handlers, heat recovery ventilators, intermittent whole-house exhaust systems, or anywhere specific ventilation rates are desired. Mixing the house air with fresh outdoor air can reduce concentrations of moisture and contaminants indoors and recharge the indoor air’s oxygen content.
There are many types of ventilation controls that including the simplest devices - manually operated twist-timers. Some of the controls that are available to automatically operate mechanical ventilation systems that are integral to most homes are described here.
Programmable Microprocessor Exhaust Fan Controls
Microprocessor-based controls can balance ventilation with energy conservation because they can be programmed to operate intermittently. Different models allow for single or dual fan speed operation. For instance, a multi-speed exhaust fan might be operated by this type of control at low speed to provide ventilation and then boosted, via occupant use of the wall switch, to high speed when local high volume exhaust is desired for mist removal after a shower. These controls eliminate user error by automatically coordinating fan speed and cycle time based on the overall volume of air in the home and occupancy, while still allowing occupants access to a full-speed fan cycle. Controls can be paired with a quiet, energy-efficient fan so that occupants are not aware of the fan’s operation. Some units come with a battery backup that will hold the programmed setting during a power failure. Tamerack’s Airetrak™ is one example of a programmable microprocessor fan control.
Controllers for the Central Air Handler Fan
Central air handler fan controllers can be pre-programmed to engage the central system fan to periodically mix indoor air (when the system is not running) and to control a motorized damper in a fresh air supply duct that connects outside air with the system’s plenum. Controlling the system’s fan operation with a control that is independent of the thermostat avoids continually running the fan. The same control can be used to engage the fresh air intake duct damper. Otherwise, air intake dampers are often triggered when the system’s fan is in operation which can over-burden a system in extreme hot or cold climates. AirCycler™ is one such control.
Integrated Exhaust Fan and Microprocessor Control Systems
An integrated ventilation system, SmartSense®, is available as a kit that includes low sone exhaust fans and switches that can be installed in any room in a home. Once the system is in place and programmed, one switch becomes the master control and all others become slaves (via a phase coupler mounted near the circuit breaker panel.) The system can be operated with up to 10 slave switches. All switches can manually operate the local fan. The master can operate any given fan based on a pre-programmed ventilation level that factors in the manual use at each location.


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Attributes

These systems introduce fresh air and/or remove stale air at timed intervals

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Ease of Implementation

Ventilation controls are easy to include in the specifications of a new project. Like the thermostat, these controls are the domain of the HVAC contractor who should provide the design and equipment and co-ordinate the installation.
Controls or systems can also be employed in remodeling and retrofit projects.
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Initial Cost  
Controls cost between $50 and $100, dependent on features and manufacturer. Whole systems, which include two or three fans and switches, will cost more.
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Operational Cost  
The operational costs of any mechanical ventilation strategy will be dependent upon the fan characteristics operating schedule, and climate.
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U.S.Code Acceptance
Switches, controls, fans and motorized dampers or other electrical equipment should be UL listed.
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Field Evaluations
Warren Builders: Site 1. Albertville, Alabama
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Installation
New construction activities related to providing for ventilation controls can be performed during typical site visits for rough-in and final mechanical/electrical installations. Controls can be fit into a single gang electrical box. Controls require an electrical current source and a direct connection to the fan that will be operated, just like switches.
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Warranty
Manufacturer’s warranties vary between one and three years dependent on product and use. See manufacturer’s literature for complete details.
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Benefits/Costs
Ventilation controls can be programmed to fit specific occupancy patterns and indoor air volume so energy losses may be minimized while comfort is maximized. Dependent on the ventilation approach that is selected, controls can operate individual room fans or the central system’s fan to exhaust stale humid air or mix and circulate room air. Some controls can also operate a mechanical damper in fresh air ducts.
The ventilation methods described here are unbalanced, or exhaust- or supply-only methods. Exhaust-only ventilation removes stale humid air while relying on air leakage through the building envelope to provide the fresh air make-up. Exhaust-only ventilation may depressurize a house while the opposite is true in the case of a supply-only ventilation scheme. Balanced ventilation strategies are explained at the link below. These ventilation controls may be used for whole house balanced ventilation systems, as well.

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