Runaround Coil Heat Recovery

With all the talk about green house gases and oil dependency, energy efficiency and specifically, energy savings, is a top consideration these days.  One of the things that you don’t hear about too often is something called a “runaround” coil.  The system isn’t really limited to a coil but, instead describes a very simple  system for absorbing heat from one air stream and rejecting it to another.  Consider a large office building or hospital application where 100% outside air is conditioned, distributed to the individual spaces, and then completely exhausted.  A runaround system is nothing more than two heat transfer coils, one positioned in the inlet air stream ahead of the conditioning coils, and the other in the exhaust air stream.  The two coils are connected by piping in which water or a glycol solution is circulated by a centrifugal pump, hence the name “runaround”.  During the summer when outdoor air temperatures can reach into the 90s and 100s, the fluid in the runaround system absorbs heat from the outside air and in the process, cools it to a certain temperature.  The heat carried by the fluid is then circulated to the coil in the exhaust air stream where it is rejected to the air.  Heat rejection occurs because the exhaust air is at a temperature lower than that of  the fluid stream.  Significant energy savings occur when the cooling requirements of the building can be reduced.  For example, a building without a runaround system has a 100 ton load.  In order to meet the load, the cooling equipment has to cool outside air from 95 to 55 degrees.  Precooling of the outside air by 5 degrees (90 degrees) reduces the load on the cooling equipment to approximately 87 tons.  Dropping the cooling requirement by 13 tons can result in significant electrical energy cost savings.  Now, what happens if evaporative cooling is employed in the exhaust air stream? If an evaporative cooler is added upstream of the runaround coil, then the air stream can be cooled further resulting in an increased heat transfer rate from the fluid to the air stream, further reducing the cooling capacity requirements of the cooling equipment.   The use of a runaround coil is not a novel idea but one whose time is coming.

Air Conditioning in the Winter?

Whoever heard of air conditioning in the winter?  It’s cold outside and you need warm air, not cold to be comfortable, right? That certainly sounds reasonable.  After all, most people are using their furnaces at this time of  the year.  You might not be aware of it but, it is possible to create enough heat enough within an enclosure so as to require cooling instead of heating.  Most homes lose heat at a faster rate than can be replaced by supplemental sources (ovens, televisions, dryers, etc). As a result, some type of heating system has to be implemented in order to keep cold weather at bay.  However, in some office buildings, for example, the number of people and machines can easily produce enough heat to require space cooling in order to keep people comfortable.   Consider for example a 40 watt flourescent light bulb.  For each watt of power, the bulb produces 3.41 BTU/hr or 136.4 BTU/hr/bulb.  Most light fixtures are equipped with four bulbs. So, each fixture produces 545.6 BTU/hr. Imagine an office space equipped with 100 light fixtures. The total heat produced by all of  these fixtures is now at 54, 560 BTU/hr.  In terms of cooling, 1 ton of cooling is equal to 12,000 BTU/hr. The lights will require a cooling capacity of 4.5 tons. This doesn’t sound like  much but, when you start adding in other loads like people and computers, the heat output can be significant.

Ford and their Windstar Axle Problem

The Ford Motor Company has recently recalled 1998 to 2003 Winstar vehicles due to a problem with the rear axle. It seems that corrosion can attack the axle and cause it to break. When the axle breaks, the driver can lose control of the vehicle and crash. It seems to me that as long as Ford has been in business, the company has gained enough experience to know how to protect the vehicle, in general, and, the rear axle,  in particular, from the effects of corrosion.  It is well known that in climates where salt is used to melt ice, the resulting residue can corrode the undercarriage of vehicles not protected. So, how is it that a car manufacturer, who has been building cars for longer than most of us have alive, puts out a product that is not protected against a well known corrosive medium? Consider for a moment that the Windstar is the only vehicle in the Ford family of cars and trucks that is subject to this problem. Ther aren’t any other recalls for a Ford manufactured vehicle wth this problem. From Ford’s viewpoint, Ford believes that owners of Windstar vehicles who are experiencing rear axle problems are trying to get out of paying for expensive repairs by filing claims against Ford alledging a defective product. Why couldn’t the Windstar be defective?

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