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Whole-House Mechanical Ventilation Strategies

Give control of air-exchange to homeowners rather than to weather or wind speed

View the ToolBase TechSpecs- Whole-House Ventilation Systems PDF file for an overview of this technology.

Photo showing damper, control and transformer.

Aside from paying the mortgage, space heating and cooling costs can be the most expensive aspect of home ownership. A well-insulated, tightly-sealed building envelope (exterior walls, roof, and foundation systems) can prevent the escape of costly conditioned air, but may have unintended consequences for indoor air quality (IAQ). While drafty, uninsulated structures allow plenty of natural "infiltration", well insulated and sealed structures may allow the build up of contaminants such as bacteria, mold spores, cooking fumes, pollen and dust. In some climates, inside and outside humidity levels may cause mildew or excessive condensation problems.

There are a number of mechanical ventilation systems that give control of air-exchange to homeowners rather than to weather or wind speed, and that can be incorporated into new or existing homes. Decisions regarding the best ventilation strategy for a particular situation should always go hand-in-hand with consideration for energy efficiency.

Below is a discussion of several types of mechanical ventilation systems and controls including Honeywell Y8150A Fresh Air Ventilation System, NightBreeze, Heat Recovery Ventilators (HRVs), Energy Recovery Ventilators (ERVs), Airetrak Controls, and Fan Recycler. Descriptions of other strategies for whole house mechanical ventilation include central air purification/ventilation/dehumidification systems, passive solar ventilation air pre-heaters, and in-line fans.


Mechanical Ventilation Systems

Mechanical ventilation systems may range from very basic - for instance, an exhaust fan and a timer - to more sophisticated systems that may be ducted to multiple locations, pre-condition the incoming air, and/or be tied into other mechanical systems in the home. A system may be custom designed by combining various individual components or may consist of a "packaged" system supplied by one manufacturer. The systems that are described here represent three possible options of mechanically introducing fresh air into the home.

Honeywell Y8150A Fresh Air Ventilation System

The Honeywell Y8150 A is used in conjunction with central HVAC fan systems. It consists of a motorized damper, a transformer, and control that contains an "intelligent algorithm". The algorithm calculates the amount of ventilation needed based on particular settings for the home. The installer enters the square footage of the home, the number of bedrooms, and the amount of outdoor air being introduced when the air handler operates and the damper is open. The latter value is obtained by directly measuring the volume of air moving through the duct with a tool such as a pitot tube. The control then opens the motorized damper the appropriate amount of time to achieve the required volume of fresh air for the home.

The algorithm is based on the ASHRAE 62.2 Mechanical Ventilation Standard (February 2003). This standard calls for the following ventilation rates:

Floor Area
(square feet)

Number of Bedrooms

 

0-1

2-3

4-5

6-7

>7

<1500

30

45

60

75

90

1501-3000

45

60

75

90

105

3001-4500

60

75

90

105

120

4501-6000

75

90

105

120

135

6001-7500

90

105

120

135

150

>7500

105

120

135

150

165

For a four-bedroom 2,000 square foot home, this is 57.5 cubic feet per minute (cfm).

NightBreeze

Developed by the Davis Energy Group, NightBreeze is a system that integrates space heating, air conditioning, whole house ventilation, and filtration. It is ideal for mild cooling dominated climates with cool nights and warm days.

Components of the system include:

  • A built-in hot water coil that circulates hot water from the boiler or water heater.
  • A variable speed blower powered by an electronically commutated (ECM) motor that uses a fraction of the blower energy used by permanent split capacitor motors. The air handler can be used with heating equipment up to 100,000 Btuh and cooling equipment as large as 5 tons of cooling capacity.
  • An outside air damper that delivers up to 2100 CFM of outside air while also filtering the air and providing relief of indoor air to the attic or outdoors.
  • A control system that integrates heating, air conditioning, ventilation cooling, and fresh air ventilation functions and optimizes the amount of ventilation cooling required to maximize energy savings and offset AC use.

The NightBreeze unit pulls fresh outdoor air into the home and exhausts stale indoor air to the attic or to the outdoors. The fresh air is filtered prior to being delivered to the home at one or more locations.

Ventilation cooling during the summer: On cool summer nights, the NightBreeze system brings in filtered outside air and flushes out warm, stale indoor air. Typically, the NightBreeze air handler operates whenever the outdoor temperature is at least 5° F cooler than the indoor temperature. A low limit temperature setting prevents the house from being overcooled during milder periods. If ventilation cooling is not sufficient to maintain indoor temperatures below the high limit setting, the system operates the air conditioning system if there is one.

The system also varies the airflow rate daily based on the historical record of indoor and outdoor temperatures. Indoor and outdoor temperatures are recorded daily. This history is used to predict temperatures for the following day, operating the fan at higher speeds if hotter weather is expected.

Ventilation heating during the winter: When the system is in heating mode, the outside air damper and fan operate once per hour to provide ventilation. The NightBreeze circulates water from your water heater or boiler through a coil that is similar to the radiator in a car. The air handler blows incoming fresh air across the coil and delivers warm air to the house. If the heating system operates at any time during a given hour, the damper opens long enough to deliver the pre-set average hourly ventilation rate. Again the fan speed will vary and the damper will remain open accordingly. If supply temperatures drop below about 100° F, the damper will close to prevent discomfort.

If the fresh air requirement is not fully satisfied while the central system is providing heating or if no heating is needed during the hour, the system will activate the fan and damper at the end of the hour. At outside temperatures below 45° F, the control will automatically activate the pump to temper incoming air. At temperatures below 35° F, ventilation is discontinued to prevent freezing.

Vacation mode: Vacation mode is used while away from home for an extended period. Minimum and maximum temperatures are programmed into the thermostat and the air conditioning, heating system, and ventilating system operate as needed to maintain indoor temperatures within these limits.

HRV/ERV

A heat recovery ventilator (HRV) can help make mechanical ventilation more cost effective by reclaiming energy from exhaust airflows. HRVs use heat exchangers to heat or cool incoming fresh air, recapturing 60 to 80 percent of the conditioned temperatures that would otherwise be lost. Models that exchange moisture between the two air streams are referred to as Energy Recovery Ventilators (ERVs). ERVs are especially recommended in climates where cooling loads place strong demands on HVAC systems. However, keep in mind that ERVs are not dehumidifiers. They transfer moisture from the humid air stream (incoming outdoor air in the summer) to the exhaust air stream. But, the dessicant wheels used in many ERVs become saturated fairly quickly and the moisture transfer mechanism becomes less effective with successive hot, humid periods. In some cases, ERVs may be suitable in climates with very cold winters. If indoor relative humidity tends to be too low, what available moisture there is in the indoor exhaust air stream is transferred to incoming outdoor air.

Click here for HRV/ERV -- In-Depth Information.


Ventilation Control systems

Today's energy-efficient homes do a great job of keeping conditioned air in. The downside is that reduced ventilation and air exchange with the outside can result in poor indoor air quality and possible health problems. Even air systems that are designed with fresh air intake do not provide ventilation or exhaust when they are not running. Economical and affordable ventilation control systems are ideal for use with exhaust fans, air handlers, heat recovery ventilators, intermittent whole-house exhaust systems, or anywhere specific ventilation rates are desired. Mixing the house air can increase energy efficiency, reduce moisture condensation problems, and increase indoor air quality.

Click here for Ventilation Control Systems -- In-Depth Information.


Energy Efficiency

Whole house mechanical ventilation systems can increase energy efficiency by controlling the amount of fresh air that enters a home. This allows the house to have a tightly sealed building envelope while still allowing an adequate amount of fresh air to enter. Some systems include a heat recovery device that captures the heat from the exhaust hair and uses it to pre-heat the incoming fresh air.

Environmental Performance

Mixing the house air can increase energy efficiency, reduce moisture condensation problems, and increase indoor air quality. A house without proper ventilation can have problems elimnating moisture and pollutants.


Easy

The ventilation control system can be incorporated with exhaust fans, air handlers, heating recovery ventilators, or intermittent whole-house exhaust systems.


Whole house mechanical ventilation strategies can range from basic systems to more complex, efficient heat-recovery systems. Adding a duct with a damper to modulate the amount of fresh air that enters a forced-air furnace would cost approximately $300. A more complex heat exchanger that extracts the heat from the exhaust air to preheat the incoming air can cost a couple thousand dollars.


Not Applicable


Honeywell Y8150A Fresh Air Ventilation System

There are no national regulatory issues related to the installation of the Y8150A. However, local requirements regarding mechanical ventilation may impact the sizing, design, and/or installation of the system.

NightBreeze Air Handler

There are no national regulatory issues related to the installation of the NightBreeze ventilation system. However, local requirements regarding mechanical ventilation may impact the sizing, design, and/or installation of the system.


Not Applicable


Honeywell Y8150A Fresh Air Ventilation System

Typically, the damper is installed in a 6" duct that runs from the outdoors to the return side of the air handler on the central heating and cooling system. The control opens the damper to introduce fresh air when the air handler operates to satisfy a space heating or cooling call from the thermostat. Once the damper has been open the appropriate length of time to satisfy the calculated requirement for ventilation, the damper will no longer open during regular heating or cooling periods. Alternatively, if there have not been sufficient heating or cooling calls to introduce adequate fresh air, the control will open the damper and activate the air handler. The control resets and begins counting every 24 hours.

NightBreeze Air Handler

The NightBreeze is typically installed in an attic where the outside air damper can most easily be located over a return air register in the ceiling of the living space. This register should be easily accessible to facilitate regular replacement of the filter. The damper exhausts indoor air to the attic and is also ducted to a louver or roof vent where fresh air is drawn in. In the event that some areas of the home might be isolated from the return air register by closed doors, transfer grilles are recommended.

The NightBreeze air handler may be located anywhere but should be as close as possible to the damper to minimize pressure and thermal losses. It is also advantageous to have the air handler centrally positioned in relation to the supply registers. The air handler incorporates a variable speed blower, a hot water heating coil, a circulating pump, and system controls. Because of the wide variation in flow and pressure requirements for different installations, a circulating pump is not included in the NightBreeze system and must be purchased separately. A pump relay is provided in the NightBreeze parts kit.

The heating coil can be connected to either the potable water supply or a closed-loop pressurized system used for space heating. By circulating hot water through this coil during the winter, the incoming outdoor air is warmed before it is delivered to the home. ¾" copper or Pex tubing may be used if the equivalent length of piping between the water heater or boiler and air handler is less than or equal to 50'. 1" piping should be used if the equivalent length is greater than 50'. The NightBreeze manufacturers recommend installing an air vent to remove air from the piping as needed and valves, unions, and a drain to facilitate flushing the piping and possible service needs. The piping should be insulated and freeze protection provided if necessary.

For summer cooling, coils from 1½ to 5 tons may be added to the NightBreeze Air Handler. Because the NightBreeze usually requires higher flow rates for ventilation cooling than for air conditioning, cooling coils should be oversized by at least one ton to minimize pressure drop while the system is ventilating.

Recommendations regarding duct sizing and minimum free vent area for registers and fresh air intake are given in the NightBreeze Installation Manual. Recommended air flow rate is 0.6 CFM per square foot of conditioned floor area. It is recommended that branch ducts and registers be sized using a maximum external static pressure of 0.3" w.c.

Controls provided with the NightBreeze include a thermostat, an outdoor temperature sensor, and an electronic control module that is installed in the air handler. The thermostat allows for cooling, heating, and vacation modes as well as short-term override settings and manual fan operation. The outdoor temperature sensor should be located out of direct sunlight and away from areas where hot air may collect such as above the roof or adjacent to a west wall. The thermostat should be located on an interior wall near the return and on the second floor in a two-story home.


Not Applicable


Honeywell Y8150A Fresh Air Ventilation System

The Honeywell Y8150A ventilation system is a low-cost means of automatically introducing fresh air into your home using your existing central heating or cooling system. The recommended amount of fresh air is calculated based on the size of your home and number of occupants. The system also tracks and controls the amount of fresh air that is introduced in order to avoid over- or under-ventilation. These features contribute to an energy-efficient means of bringing fresh air into a tightly sealed home.

The retail cost of the Y8150A is $275. This includes the motorized damper, the control, and the transformer.

NightBreeze Air Handler

The NightBreeze ventilation system is a good ventilation cooling strategy in moderate climates. It provides a means of automatically introducing fresh air in a controlled manner and reduces compressor cooling energy use and expense. The interface with the central space heating and cooling system insures that indoor temperatures are maintained within the specified comfort range. The variable speed air handler also helps assure energy efficient operation.

Disclaimer: The information on the system, product or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter by the NAHB Research Center. There are no warranties, either expressed or implied, regarding the accuracy or completeness of this information. Full reproduction, without modification, is permissible.