10/15/2015

Centralized Whole House Ventilation Systems versus Decentralized Spot Balanced Ventilation

When you are building or renovating a house, you want to install the best possible ventilation system to ensure the healthiest, most comfortable, and most energy efficient home. Investing in an ERV is a great way to ensure that your ventilation system won’t throw money away in the form of heated or cooled air. However, there are many types of ERVs. One major consideration when selecting an ERV is whether to choose a centralized or decentralized ventilation system.

Consideration 1: Ventilation Effectiveness

Centralized ventilation systems are generally the best at circulating air and maintaining neutral pressure throughout an entire home. A decentralized system that relies upon small ERVs to circulate air in specific rooms may still be effective at supplying fresh and exhausting stale air in those rooms. In homes where all rooms are used often, a centralized ventilation system usually makes more sense. In homes where rooms or areas are remote from the rest of the house (like above the garage for instance) or often unused and blocked off, decentralized ventilation may be preferable.

Consideration 2: Energy Efficiency

It is often necessary to install separate exhaust systems in rooms where a lot of moisture is produced when a decentralized ventilation system is used. There are ERV bath fans that can be installed, but these are generally not as efficient as centralized ERVs. Installing many single-room ERVs may work to obtain results comparable to a centralized ERV when it comes to ventilating the space, but the amount of heated or cooled air lost and the energy required to power the individualized units (watt/cfm) will often play in favor of a centralized solution.

Consideration 3: Noise Pollution

Many small ERVs will invariably make more noise than one centralized unit. Decentralized ventilation systems rely on fans that are installed in each area to exhaust stale air and pump fresh air into the home. Centralized systems utilize a centralized fan and ducts to distribute fresh air, dramatically cutting down on noise pollution. When a centralized fan is used, it is also possible to buffer the sound so that noise from the fan will not be heard in living areas.

Consideration 4: Penetration of Thermal Envelope

ERVs require a break in the thermal envelope of the building in order to both exhaust internal air and take in external air. Breaks in the thermal envelope naturally reduce the building’s ability to retain heated or cooled air and to keep out unconditioned air. By this reasoning, a centralized ventilation system reduces inefficiencies by only penetrating the building’s thermal envelop in two places (exhaust and intake) and makes it much easier to replace filters.

Consideration 5: Ease of System Control

Centralized ventilation systems can usually be controlled using one interface. This is much easier than going from room to room and altering settings on individual units. However, in some cases, it makes more sense to be able to adjust settings to cater to different needs in different spaces.

Consideration 6: “Cascade” Ventilation Effect

The “cascade” ventilation effect occurs when fresh air is piped into bedrooms and then moves through open living areas en route to exhaust fans. The cascade effect reduces the need for supplies in open living areas, thus reducing costs while maintaining adequate home ventilation. It is not possible to take advantage of the cascade effect when using a decentralized approach to ventilation.

Consideration 7: Installation Costs

Installation costs may be much more for a centralized ERV than for through-wall ERVs. When older homes are being renovated, it may be necessary to run new ductwork throughout the home in order to install a centralized system. In this case, it generally makes more sense to use a decentralized approach to ventilation. When building a new home, however, a centralized system is usually preferable.