Why do we need Make-Up Systems
1. Our homes have become extremely air tight with the result that fresh air replacement from outside via air seepage, can no longer be relied upon to bring in clean air. The result is that the air quality on our homes becomes very unhealthy. So in order to improve this air quality we need to find a way to bring in fresh clean air and evacuate or clean the stale air. This is achieved with make up air systems. You can liken the situation to living inside of a sealed plastic bag - without make up air - particularly in winter the air quality becomes very poor and unhealthy.
2. Now if you add a kitchen range hood that evacuates large amounts of air, the situation actually becomes far worse - we are exhausting the air from our sealed plastic bag example above and without any make up air bringing air back into the "plastic bag", the environment actually becomes depressurized - the pressure inside the bag rapidly becomes less than the pressure outside - the results can be catastrophic as our heating equipment such as fireplaces, hot water tanks and furnaces rely on balanced air pressure to exhaust the poisonous gases to the outside. When a home becomes depressurized these gases actually get drawn back into the environment with the lowest pressure - the "plastic bag" - our home.
So what do make-up air systems do. Very simply they are linked via pressure switches or electronic switching to suck air back into the home as it is exhausted and to constantly bring in a supply of fresh air. By way of example, when we use our range hood that is say exhausting 600cfm (cfm = cubic feet per minute - visualize a block of air that is 12"x12"x12" - that's 1cfm), now with a 600cfm range hood that is 600 of these blocks of air every minute leaving our "plastic bag" type home - under this situation the average home would attain a negative air pressure situation very very quickly and the dangerous gases from our appliances would invade the home and its occupants.
The make-up air system would be activated before this negative air situation has had chance to develop and would pull air back into the home to replace the exhausted air - make-up air system must of course also heat this air before bringing it back into the home in winter and cool it in summer.
So that very simply is how make-up air systems work and why we need them.
Below please find copy from the Uniongas website on make-up air:
http://www.uniongas.com/business/gastechnology/productsservices/iaq/iaqMakeupAir.asp
In most cases, the need for ventilation air is achieved by the addition of a make-up air unit(s). These units are essential to a building's mechanical operation and to the health and comfort of its occupants. By providing a controlled quantity of clean, conditioned ventilation air to common areas of the building, they:
•Reduce drafts, dust and dirt entering the building;
•Replace air exhausted by equipment such as kitchen or bathroom fans or process or industrial exhaust fans;
•Reduce odours.
A make-up air unit consists of a fan and a heat-exchanger component as well as filters and dampers. Gas-fired units are available in many sizes to meet building ventilation needs and are supplemented by a variety of control components (both temperature and air quality) and operating strategies. Control systems are important as they can be designed to handle 100% outdoor air or to mix outdoor air with re-circulated indoor air. Mixed air systems can be electronically controlled. Heating can be provided at fixed or variable heating rates and control strategies for these systems can also vary from simple manual systems to computerized options.
Depending on the application, make-up air units can be installed either on rooftops or indoors. High-rise buildings generally install their units on rooftops, where they are mounted on either a curb or metal roof frame, then connected with the building's electrical and duct work system. In walk-up apartments, units are often installed in utility or attic rooms and conventionally ducted to feed air to the corridors and common areas.
A variety of features are available that will enhance the performance of make-up air units, including:
•Heat reclaim coils or heat wheels, to recover waste heat;
•High efficiency filtration to maintain air quality and automated controls governing both temperature and air quality to minimize energy consumption - including capacity control utilizing two-stage or modulating gas valves that will match the unit's output with your building's needs.
Electric make-up air heaters can also be converted to natural gas by installing a heating coil in the duct, which is heated by hot water that is supplied by a gas-fired boiler.
