Control of health hazards in an air handler

Details Control of health hazards in an air handler Control of health hazards in an air handler

1998-10-14

2001-08-28

McKane, Elizabeth (Department: 1744)

Chemical apparatus and process disinfecting, deodorizing, preser

Process disinfecting, preserving, deodorizing, or sterilizing

Using direct contact with electrical or electromagnetic...

C422S121000, C062S078000, C096S224000

Reexamination Certificate

active

06280686

ABSTRACT:

NOTICE OF COPYRIGHTS AND TRADE DRESS
A portion of the disclosure of this patent document contains material which is subject to copyright protection. This patent document may show and/or describe matter which is or may become trade dress of the owner. The copyright and trade dress owner has no objection to the facsimile reproduction by any one of the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright and trade dress rights whatsoever.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to control of health hazards in air handlers and more particularly to eliminating organic matter in heat exchangers in cooling and heating systems.
2. Description of Related Art
One mature industry that is economically sensitive to costs is the heating, ventilation and air conditioning (HVAC) industry. Because of the competitive nature of both the construction and HVAC industries, HVAC systems must be inexpensive to install. Of a more global interest though, is the cost to operate and maintain HVAC systems. Often, a building owner will replace an aging HVAC system as the reduction in operating and maintenance costs can offset the retrofit cost, sometimes in a matter of months.
Broad social and energy policies also favor more efficient HVAC systems. In these days of electricity deregulation and conservation, it has become even more important to conserve energy consumption. Recently, entire electrical grids have shut down on very hot days in part because of the huge demand of HVAC systems running at extreme capacity. Furthermore, energy conservation translates directly into improved environmental conditions and decreased reliance upon foreign petroleum.
HVAC systems are typically comprised of fans and ductwork for moving air where needed. An HVAC system will include a cooling and heating section for, respectively, cooling and heating the air. In most HVAC systems, air is drawn in, filtered, cooled and dehumidified or heated and humidified, and then delivered to a room. The greatest portion of this air is drawn from the conditioned space for recirculation through the HVAC system. Considerable effort has been made to make these components more efficient
One of several recently used methods of saving energy in an HVAC system includes the use of variable frequency drives on any motor used in a HVAC system. Variable frequency drives can also be used to selectively increase air flow. When and if the system load decreases, this can be sensed and the motors in the HVAC system will be slowed to an equilibrium value to save motor energy consumption. Another method is to reduce the design amount of outdoor air to eliminate having to condition it. Another method is an economizer cycle that utilizes 100% outdoor air when its ambient temperature is suitable for cooling the space. Another method is to replace aging equipment with newer, more efficient and more powerful equipment.
One other factor impacting design and operation of HVAC systems is indoor air quality (IAQ). One major factor in IAQ today is the amount of outdoor air introduced into an otherwise sealed space serviced by an HVAC system. The HVAC industry has adapted standards for the introduction of outdoor air into spaces serviced by an otherwise closed HVAC system These include offices, residential, commercial, industrial and institutional spaces, as well as the interior of vehicles such as cars, buses, planes and ships. In addition to controlling indoor air for occupant comfort, the goal of HVAC systems is to provide air with reduced levels of particulates, gases and bioaerosols, be it for semiconductor, pharmaceutical or food processing facilities, hospitals, schools or offices and now the home.
Most ventilation systems today include a cooling section. The cooling section includes a type of heat exchanger typically referred to as a “cooling coil,” through which air is forced and cooled. This cooling coil operates thermodynamically to remove both sensible and latent heat from the forced air. Cooling coils typically are made using aluminum fins over refrigerant tubes which have been formed into a desired shape. Essentially the same coil arrangement is used in all cooling systems, whether in HVAC systems for occupied spaces, or for refrigerators and freezers.
A similar configuration is often used in heating sections, though the thermodynamic operation is opposite to that in a cooling section. The heat exchanger of a heating section often comprises a coil. Water (or some other fluid) of an elevated temperature passes through the coil to elevate the coil's temperature. The heating coil is fashioned in a manner to promote heat transfer from the water to the heating coil. The heating coil is further fashioned to promote heat transfer from the heating coil to air which is forced across and through the heating coil.
One important measurement of a heat exchanger is its heat transfer efficiency. A heat exchanger's efficiency is essentially its ability to absorb or impart heat to an airstream. The more heat that a heat exchanger can transfer per unit of time, the greater its efficiency.
A cooling system has an efficiency defined as:
K
r
=
Q
2
Q
1
-
Q
2
A heating system has an efficiency defined as:
K
h
=
Q
1
Q
1
-
Q
2
Where, for both heating and cooling systems:
K=efficiency (coefficient of performance)
Q
2
=amount of heat absorbed by heat exchanger
Q
1
=amount of heat rejected by heat exchanger
For typical cooling systems including a cooling coil and heating systems including a heating coil, the difference between the heat absorbed Q
2
and the heat rejected Q
1
is the amount of work W performed.
Another important measurement of a heat exchanger is its pressure drop. A heat exchanger's pressure drop is essentially the resistance of the heat exchanger to air flowing through it. Pressure drop increases as the result of a decrease in open area, decreased open area increases the interstitial velocity between the transfer plates reducing the time the air is in contact with the transfer medium.
Under the ideal gas law (PV=nRT), the temperature of the air actually increases slightly as it passes through a heat exchanger. However, in both heating systems and cooling systems, this temperature change is inconsequential.
As a normal consequence of the process of cooling air, several things occur. One is that vapor (latent heat) is removed from the air. As moisture, it collects on the coil fins and/or anything else nearby which is below dew point, including the ductwork. Typically, a drain pan is positioned below a cooling coil. The drain pan is considered an integral part of the heat exchanger. The collected moisture runs down the coils fins and into the drain pan under the force of gravity. Water that collects in the drain pan flows away through a drainpipe equipped with a trap.
Another is that organic matter impinges and collects on the cooling coil fins from the air passing over them. Though the fins of the cooling coil appear to be smooth, in fact, when viewed under a microscope, they can be seen to have an irregular and somewhat pitted surface. The organic matter can therefore adhere easily to the damp and rough surface of the cooling coil.
Another consequence is that the cooling section is dark and at off times, it will be warm. Though when operating it will be quite cold, the cooling section will have varying cycles of cooling. When not cooling, the cooling coils typically reach room temperature.
Similar effects are encountered with heating coils, though typically to a lesser degree than with cooling coils.
Altogether, these consequences produce an environment in which molds and bacteria can grow and thrive. Over time, a heat exchanger can become near fully encrusted with microorganism activity bound to an organic substrate. The spores and products of metabolism from a heat exchanger are easily entrained into the airstream.
The drain and drain pans also become a growth environment for mold and bact

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