HRV+vs.+ERV




 * Every tight home needs a mechanical ventilation system- three most common choices are exhaust-only, central fan integrated supply and balanced ventilation
 * Balanced ventilation- either ERV (energy-recovery ventilator) or HRV (heat-recovery ventilator) is the preferred system for passive, green buildings
 * Balanced systems are often the most expensive to install, but over time have the lowest operating costs of any ventilation system
 * **HRV**- pulls out fresh air while simultaneously exhausting stale are from the home
 * In most cases, fresh air is delivered to bedrooms and living room and stale air removed from bathroom, laundry room and kitchen
 * Both fresh and stale air streams run through HRV
 * Core of the appliance allows for some heat from the warmer air stream (stale air in winter, fresh air in summer) to be exchanged with the cooler air stream
 * Basically: it recovers some of the heat that would’ve been exhausted
 * DOES NOT mix the two air streams
 * **ERV**- does everything that an HRV does
 * **//THE DIFFERENCE://** the ERV also allows for some of the **//moisture//** to be interchanged between the humid and dryer streams (humid stream is often stale in winter, fresh in summer)
 * Transfer of moisture = enthalpy transfer, occurs with very little mixture of the two air streams (stale and fresh)
 * Cross-contamination for the UltimateAir RecoupAerator (one of the best available ERVs) is around 9.6%
 * **//BIG IDEA://** HRVs provide most of the benefits that an ERV does, but does not have humidity exchange
 * Lowering humidity is intended to prevent moisture damage to a house, however this only occurs naturally with normal ventilation systems when the outside air is cooler (less moist,) warmer outside air actually makes inside of house more humid


 * Ventilation in hot vs. cold climates
 * Warm climates: When HRV/ERV ventilates an air-conditioned house (important requirement- heat exchange doesn’t work in house without AC), the cool exhaust air helps to suck heat out of incoming (aka warm) fresh air. ERV also removes most (not all) of moisture from fresh air. Better choice for warm climate: **//ERV//**. This is because while both will introduce more moist air (because of outside contact) for AC to deal with, energy load is less with an ERV.
 * Cool climates: Depends on how large house is, how many inhabitants/lifestyle, and how tight envelope is.
 * In a small, tight-enveloped, energy-efficient house of less than 2,200 square feet in a cold climate (our SD house in Vermont, for example): houses maintain 30 or 35% relative humidity, therefore don’t need ERV
 * BOTTOM LINE
 * Small, tight house in cold climate: **//HRV- this could apply to our SD house if placed back in Vermont//**
 * Large house in cold climate: **//ERV//**
 * Hot, humid climate: **//ERV//** will be more energy efficient than HRV
 * Recommended models: UltimateAir RecoupAerator 200DX ERV, Venmar EKO 1.5 HRV
 * In order to ensure best efficiency, must install proper duct work

Source: []

Complicated study on energy efficiency of various ventilation systems in different scenarios : []