Table of Content
- Types of Whole-House Ventilation Systems
- Installing A Whole House Fan
- Jorge and Paul's Adventure with HRV
- Evaluation of the Performance of Houses with and without Supplemental Dehumidification in a Hot-Humid Climate
- Improving Air Circulation in Baldwin County Homes
- Measure Guideline: Selecting Ventilation Systems for Existing Homes
- Mobile Field Kit
These typically include override switches to turn on exhaust fans when desired. A free tool used to calculate the required minimum flow rate of dwelling-unit ventilation. A report describing six mechanical ventilation strategies that were evaluated for their ability to control indoor humidity levels over 14-day periods with simulated occupancy. A calculation procedure to account for the differences in combining balanced and unbalanced ventilation systems with air infiltration. 7.5 If system utilizes the HVAC fan, then the specified fan type is ECM / ICM (4.7), or the controls will reduce the standalone ventilation run-time by accounting for hours when the HVAC system is heating or cooling.
Bathroom exhaust fans have been the standard ventilation practice for decades. Most often the fans are installed in bathroom ceilings with a small duct (typically 4-inch diameter) that carries air to an outdoor termination of some type. While many homes already have exhaust fans, many older fans do not perform at the desired or rated ventilation rates.
Types of Whole-House Ventilation Systems
For every cubic foot of air exhausted out of the building, a cubic foot of air has to come into the building from somewhere. Again, that "somewhere" is the many air leaks through the building envelope that connect the conditioned space to unconditioned spaces or directly to the outdoors. With this strategy, the outdoor air entering the building is not directly filtered or conditioned.
Refer to the manufacturer’s literature to ensure that the dampers are compatible with the controller. In addition to the motorized damper, a manual balancing damper in the outdoor air duct may help adjust the volume of outdoor air introduced into the system. There are a wide array of after-market boost switches and timers that work with many exhaust fans. Detailed descriptions of ventilation types are provided below for exhaust systems, central fan-integrated supply systems, HRVs, and ERVs. Ventilation systems, including exhaust-only systems and improperly balanced ERVs and HRVs, can depressurize a home, pulling more air from the home than is brought into the home.
Installing A Whole House Fan
Sensors and controls that trigger closure of outdoor air intakes during periods of high humidity are recommended in very humid climates. Similarly, sensors and controls that automatically trigger closure of outdoor air intakes or enable manual closure during periods of poor outdoor air quality, for example if wildfires are occurring nearby, are also recommended. Similarly, sensors and controls that automatically trigger closure of outdoor air intakes or enable manual closure during periods of poor outdoor air quality, for example, if wildfires are occurring nearby, are also recommended. ENERGY STAR-rated exhaust fans are recommended for most applications; the most obvious benefit of these fans is lower energy consumption. ENERGY STAR requirements for bathroom exhaust fans call for fans to deliver a minimum of 2.8 cfm/Watt.
Outside of hot, humid climates, selecting ERVs or HRVs is not as straightforward. Some manufacturers provide recommendations or even maps of the country showing which type of system is most appropriate, but the recommendations vary from manufacturer to manufacturer. One of the appealing features of CFIS systems is low maintenance, but this does not mean “no” maintenance. Regularly check the air intake to make sure it is free from debris (leaves, grass clippings, trash, bird nests, etc.).
Jorge and Paul's Adventure with HRV
Sometimes, it is desirable to operate the system for less time at a higher airflow rate. For example, when the fan used for ventilation is also used for heating or cooling, it can consume significant amounts of energy. Cycling the system to turn on for 20 minutes or less per hour is a good energy-saving strategy, particularly when it is combined with a smart controller that accounts for system runtime when the system is heating or cooling the dwelling. A smart controller set for 20 minutes per hour will only add system runtime if the system doesn’t operate for at least 20 minutes per hour to provide heating or cooling.
As with all ventilation systems, it’s important to measure the delivered airflows and make sure they meet specifications or requirements. Measuring flow rates at each register is the only practical way to check system balancing. In Florida, for example, air inside conditioned homes is generally cool and dry.
Evaluation of the Performance of Houses with and without Supplemental Dehumidification in a Hot-Humid Climate
The two ducts cross in a heat exchanger where heat is transferred heat from the warmer duct to the cooler duct. In the winter, heat from the outgoing air is transferred to the incoming cold air; in summer, heat from the incoming air is transferred to the cooler exhaust air. The incoming air can be evenly distributed throughout the house via the central air handler and duct system. The main difference between an HRV and an ERV is that an ERV is able to transfer moisture as well as heat from the more humid air to the drier air. Local exhaust ventilation, such as kitchen and bathroom exhaust fans, are typically intended to run intermittently to remove contaminants near where they are generated. Most of the HRVs and ERVs discussed here are ducted systems—i.e., two ducts run from the unit to the indoors and two ducts run from the unit to the outdoors.
Complex systems are not only more expensive to install, but they are generally more maintenance intensive and often consume more electric power. For most houses, attempting to recover all of the energy in the exhaust air will probably not be worth the additional cost. Only some HVAC contractors have enough technical expertise and experience to install them. A balanced ventilation system usually has two fans and two duct systems. Fresh air supply and exhaust vents can be installed in every room, but a typical balanced ventilation system is designed to supply fresh air to bedrooms and living rooms where occupants spend the most time.
Exhaust-only ventilation strategies use exhaust fans located in the bathroom, kitchen, laundry room, or some central location to pull moisture and contaminants out of the home. For more information on selecting and installing kitchen and bath fans for local and whole-house ventilation, see the Solution Center guides Bathroom Exhaust Fans and Kitchen Exhaust Fans. Energy recovery ventilators , function like HRVs but move to transfer both heat and moisture. Turning on the air handler when the ERV/HRV operates can solve this short-circuiting problem, but this increases electricity consumption dramatically and is not recommended.
Ducts should be sealed and the ducts running to and from the outdoors should be insulated. If the ERV or HRV is installed in unconditioned space (e.g., in a vented attic), the ducts carrying exhaust air and tempered outdoor air should also be insulated. In many older homes in colder climates, indoor air during the winter is often uncomfortably dry—so dry that many people use humidifiers. An ERV can help retain moisture within the home and potentially improve comfort. Make sure a duct can be run from the return plenum to the outdoor air intake location within the project’s scope.
This report discusses where, when, and how much ventilation is appropriate in a home, including some... If flow measurements do not match specifications or design targets, adjust the controls if appropriate. If the desired flow rates are hard to achieve, inspect the duct system, registers, and exterior terminations for obstructions. If controls have advanced features (e.g., timers, flow boosts, etc.), ensure that these functions are working properly. In very airtight homes in cold climates, especially smaller homes with lots of moisture generation, indoor air humidity can be uncomfortably high.
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