Balanced Ventilation - Essential for a Healthy & Energy Efficient Home

Humans take oxygen from the air they breathe and exhale CO2 and water vapour. This means that the occupants in a home with closed windows will very quickly change the normal balance of gases in the air, and the moisture content of the air will go up. A person sleeping in a closed bedroom may wake up feeling lethargic and perhaps even with a headache because of the lack of oxygen. Cooking, showers and baths, wet towels on heated towel, all add large quantities of water into the atmosphere. If the water in the air (humidity) is not addressed, the house will become damp, creating ideal conditions for mould and mildew, which greatly increase the risk of respiratory diseases such as asthma. Asthma is a significant problem in New Zealand with the risks being higher for babies and the elderly.

NZ Regulations require a minimum rate of 0.35 air changes per hour however, this should be regarded as the absolute minimum. To avoid energy loss, windows should be kept closed. There are other good reasons to have windows closed – for security, for control noise and to keep out dust and pests. To achieve the goal of fresh air and energy efficiency, a ventilation system is essential in a modern home.

The solution for a healthy and energy efficient home is a mechanical ventilation system which provides balanced ventilation with heat recovery. At the heart of the system is an Air Handling Unit (AHU), connected to suitably placed vents by ducting.

Balanced ventilation is achieved by having 2 identical fans, one for incoming air and one for outgoing air.

Heat recovery is achieved by passing air through a crossflow heat exchanger – the exiting air giving up its energy to the incoming air.

In the summer when the house may need to be cooled, the heat exchanger can be bypassed and the hot stale air exits without heating the incoming air.

There are multiple factors to be considered before selecting a balanced ventilation solution. The capacity of the AHU must match the size of the house and pressure loss and airflow calculations are required to ensure the system will deliver the required volume of air to each room. Vents need to be carefully located to ensure optimum airflow throughout the house. Ducting will be installed in a way to minimise pressure loss.

It is important that a homeowner understands what a balanced ventilation solution is designed to deliver – namely fresh air, with a minimum of energy loss. Fresh air is essential for a healthy home and a healthy living environment is the primary benefit of the system. To achieve this, the system needs to run continuously.

A balanced ventilation system is not intended to heat or cool the home. There are many factors that affect the temperature and therefore the comfort level of a house. Comfort is also a highly personal thing. Heat sources include the sun, cooking, body heat, as well as home heating solutions. Cooling solutions include shade from trees or curtains. Many homeowners will supplement the natural heating and cooling sources with a heat pump.

Although not designed as the heating/cooling source, a balanced ventilation solution will contribute positively to the heating or cooling of a house. In a heated house, ventilation results in dryer air (lower humidity) and dryer air feels warmer and is easier to warm. With the windows closed, heat from the passive energy sources will be retained within the house and most of that energy will be retained by the heat exchanger. On a sunny winter’s day, many houses may feel comfortable without any additional heat source. The circulation of air throughout the house will have the effect of transferring warmer air to the colder side of the house.

In a house that is being cooled, the heat exchanger will cool the warmer incoming fresh air. It is important to note that most heat pump wall units only cool recirculated inside air, so it is essential to run the ventilation system at the same time.