Ventilation heat recovery.

Heat Recovery Ventilation

THE CONCEPT OF VHR

We breathe by inhaling air and utilising the oxygen content and exhaling the waste. We all work in conditioned offices, shops, factories and pay little attention to our homes and the quality of air we breathe in there.
Buildings need to breathe in a similar fashion to us to maintain a fresh and habitable state. We open windows to “air” our houses and refresh them.
We lose heat by this method and effectively throw our hard earned euros out the window as we have had to pay dearly for the privilege of heating our homes.
A certain amount of air changes in any habitable building are required to maintain this freshness of air. This means that an amount of air needs to be taken in and the same quantity extracted out. The problem is that most of the time the external air is at the incorrect temperature for our consumption and can be costly to heat or cool to our desired temperature.
The solution to this problem is to use the heat or cold from the air being exhausted to temper the incoming fresh air.
As this is a process of recovering heat from the outgoing air, it is called Ventilation Heat Recovery.

HOW IT WORKS

It works by passing the two air-streams , the incoming and the outgoing , close by each other in a heat exchanger without actually mixing the two. This enables the incoming fresh air to be heated or cooled by the outgoing exhausted air.

The system is in effect an AHU ( Air Handling Unit ) in your attic / roof space with air ducts running to / from it to every room in your house. The AHU has a no. of key elements to it. It has 2no fans , one for exhaust and one for fresh air intake / supply. It also has the heat exchanger where the two different air-streams will travel through , with the air to be exhausted heating / cooling the supply air. The AHU also has filters to clean the air and remove impurities before it is consumed.

WHY HEAT RECOVERY

In the current days of global warming and serious environmental issues we are all urged to conserve energy by as many methods as we can. We can all contribute to this by making our homes as energy efficient as possible. It is increasingly more important that we strive to stray away from oil based energy products. ( Oil is due to hit all time high and natural resources of same depleting all the time ).

Ventilation Heat Recovery utilises tiny amounts of electricity to power the fans in the AHU , ( comparable to running 2 no 75W light bulbs ) so we would claim , given the efficency of the unit, a significant reduction in your annual energy bills.

Ultimately this means you are recovering heat from your outgoing air and heating up your incoming fresh air so your heating thermostat doesn’t allow the boiler to “kick in” as frequently.

This type of concept is not new and has been used by our friends in Scandinavia and Canada for decades but is becoming increasingly popular in mainland Europe in the last ten years or so.

Like all technologies, improvements have been made to design year upon year and the current efficiencies are almost doubled in the recent years.

The system we use boasts an efficiency of 92% in certain conditions. This means the fresh air supplied through your AHU is almost at the same temperature as the air being exhausted irrespective of how cold or hot the external temperature is.

The Ventilation Heat Recovery system is not designed to replace any heating or cooling system in the domestic environment but to compliment them and increase the total energy efficiency of our homes.

Installation

The AHU is located in the attic and the network of ducts / pipes are installed in various diameters of PVC piping. See previous diagrams for simplification of installation. All terminations of ducts in rooms are a ventilation grille. Through this grille the air is either extracted or supplied depending on the room.