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Heat Recovery from Ventilation systems

Conservation of energy is not a matter of choice, but a matter of compulsion. One may afford to waste it, but one cannot waste it from a moral and economic point of view. Research in this field has been going on since many yeas, and new ways and means to conserve energy have been devised. One such popular method is recovery of heat from ventilation systems. This essay deals with various aspects of recovery of heat from ventilation systems, inclusive of the basic technical functioning, and its economic implications. This system is extremely useful in extreme atmospheres where heating and cooling of air is frequently required.

It is a necessary investment which gives the biggest return to the human being : good health. Air within our house, is hot and is exhausted. The air coming into the house is cool and clean. The incoming and the out going air cross each other in an enclosed module, and there is a exchange of heat. The outgoing air transmits the heat to the incoming air, and thus the in coming clean air is warmed up when it enters the premises. There two flows of air do not mix with each other but only exchange the heat. The module in which this exchange takes place is known as “heat recovery ventilator. ” Working principle of HRV.

( healthandenergy,com) The above figure demonstrates the working principle of a heat recovery system. 1. The stale air from kitchen, bathroom, laundry is collected by a set of ducts. 2. Fresh air is collected by another set of ducts from the outside environment. 3. The two flows of air, cross each other in the heat recovery ventilator. As a result, the heat is exchanges, the incoming air becomes warm and the out going stale air dissipates heat. This exchange takes place in the enclosed module and there is no mixing of air. 4. Up to 85 percent of energy is recaptured by the heat recovery ventilator. Filtered and

preconditioned air is circulated through ducts in various areas of the residence/building. In the summer months the process is just reversed. The incoming fresh and warm air dissipates energy within the HRV module and that is absorbed by the out going stale air. As a result the incoming air is always conditioned according the requirements. Why not open the windows? One may ask. Sure. It does provide ventilation, but it cannot clean the incoming air, nor can the rate at which it is coming in can be controlled. Most important of all, it does not provide recovery of heating or cooling energy to almost 85 percent.

In the current fashion of erecting tight buildings, lack of proper ventilation accumulates the stale air within the building. This stale air is very moist in most of the cases, and contains the exhaled carbon dioxide. If not driven out of the building, it can cause severe health hazards to those living within the house. So, even if the building is conditioned well, to save the energy costs, it does not have an adequate exchange of outflow of stale air with the incoming air. This signifies the importance and the utility of the HRV unit. It aids in giving air, which promotes

good health. An energy efficient air conditioning system does not have any control on the moisture built up within the closed environment of a house or a building. Each person, on an average puts back about 6 pounds of water, while performing various activities, including breathing, cleaning, washing and cooking. The American Lung association recommends two steps to uncomfortable and expensive ventilation and provides ventilation which is comfortable and safe. These steps are : 1. Use HRV to get fresh unpolluted air and remove the stale, humid polluted air, while saving on

the cost of energy. 2. All the leaks through which air, dust, insects or cold drafts are likely to enter the house. The humid air within the closed building is not only unsafe for living beings but for the structure of the building also. Moisture can cause damage to the wood, color, wallpapers and the walls of the building. The ultimate result is that the structure becomes weak and if the damage goes unchecked, it may crumble also. Moreover, the exhaled air in a tight home contains carbon dioxide, which is dangerous if not checked and thrown out of the building. Breathing air which

has high level of carbon dioxide, can cause chronic ailments like asthma and allergy. Breathing fresh air is vital for health, and HVR is the ideal solution for that. One of the outstanding feature of HVR is hat it equalizes the amount of air taken in and the amount thrown out, in quantitative terms. Unlike conventional exhausts which create partial vacuum within the building, HVR perfectly balances both the flows. Ordinary systems create partial vacuum which causes radons, one of the cause for lung cancer. The vapor which condenses in the cool basements gives birth to micro organisms that emit bad odor and

dangerous volatile organic compounds. In the continent of North America, the regions covered by Canada and artic ocean are categorized as those which require HRV installations. The southern tip of Canada, north and north east and west of the USA are categorized as those in which HRV is recommended. South and South East USA are categorized those which require energy recovery ventilators. While Heat recovery ventilators are required for cold regions where heating seasons are longer. Whereas ERVs are sued where climate is warm, more humid and has long cold seasons.

While deciding the sizing of the HRV, one has to do some simple calculation. Generally these are sized to ventilate the house at a minimum rate of 0. 35 air changes per hour. The size can be calculated by taking the square footage of the house, and multiplying it by the height to get the cubic volume. Divide this figure by 60 and multiply it by 0. 35. This gives the required size of the HRV. In North American continent, Canada has been aggressive in implementing the use of HRV. It has a national law on ventilation. There were 125,000 units sold in Canada in 1992. On the

other hand, USA is not that aggressive. Only three states have ventilation laws and not more than 15,000 units were sold in the corresponding year. (Heat Recovery Ventilators) A few important design considerations while installing a HRV are as follows: 1. The fresh air intake must be located away fro the laundry or furnace vents. 2. For each bedroom and each common area, a separate supply inlet must be installed. 3. A return outlet must be installed for each high moisture area like the kitchen or bathroom. 4. Return outlets must be within one foot from the ceiling and 10 ft away from an oven or a

cook top 5. The duct runs must be as short and as straight as possible. 6. All the ducts must be insulated and all the joints sealed. 7. A drain must be installed to catch a condensate. Generally a HRV cost ranges between $ 1000 to $ 2500, depending upon its size. This expenses are paid back when the benefits to the health and the savings on the electricity from the heat recovered are calculated. A typical HRV requires electricity to run the fan, and this cost may vary between 0. 40 to 1. 00 dollar per day. Manufacturers of HRV offer many optional features to their products also.

These are inclusive of: 1. Heat recovery with or without moisture transfer 2. Defrost control or pre heater system to prevent ice build up on recovery module 3. Single/multiple speed controls 4. Pollutant sensor controls 5. High efficiency air filters for incoming air. Regular minimal maintenance will prove beneficial in a long run. These steps include: 1. The air filters must be replaced every 3 months 2. The outside hoods must be cleaned every year 3. The energy recovery core needs to be cleaned every 6 months 4. The condensate drain and pans must be cleaned every 6 months. 5.

The fans need to be cleaned every 6 months and grills, and the duct work must be inspected every year. (Huelman Pat & Oslon Wanda) Conclusively it can be said that in the atmospheric conditions hat prevail across the continents of North America and Europe, heat recovery ventilators are a necessity. While it has several benefits, the biggest one is that it prevents one from getting trapped into chronic illness, like asthma or cancer. No technology can revive a patient completely from chronic illness, and seeing to the preventive characteristics of a heat recovery ventilator, it is a very powerful toolwhich can keep such types of illness, miles away. Fresh air is the biggest gift of HVR. It is one of the most intelligent, wise and necessary investment, which is instrumental in giving the greatest asset to its owner: good health.

References :

1. Heat recovery ventilators, Retrieved on 2 October 2007 from: < http://healthandenergy. com/heat_recovery_ventilators. htm > 2. Heulman Pat & Oslon Wanda, [2007] University of Minnesota, Common questions on heat recovery ventilators, retrieved on 2 October 2007 from: < http://www. extension. umn. edu/distribution/housingandclothing/DK7284. html >

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