Man Is Awash

If the air in which man lives can be compared to the water of the ocean, cannot the additives to the air be compared to the salt in the water? Man cannot drink ocean water and he cannot breath some of the additives. He can tolerate and even enjoy the addition of salt in finite quantities to the food he eats but must concern himself with its effect on the other bodily functions.

Among the additives that are delivered into the air we breathe and that influence the manufacture of our products are items listed herein. Some of these are added by nature, some by the manufacturing processes and some by the changes of state required by man himself. The human body is obviously always in a state of energy conversion and such items as food are necessary to support that conversion.

The EPA (Environmental Protection Agency) is in the business of keeping these processes in balance. Its elaborate listings on its website have allowed us to glean certain data applicable to the 48 counties that we consider our trading area. The quantities listed are on a rounded tons per year basis and are emitted by some 1,219 sites listed on the website and within that 48 county constraint.
CO Carbon Monoxide 185,000 tons
NOX Nitrous Oxide 193,000 tons
VOC Volatile Organic Compounds 61,000 tons
SO2 Sulfur Dioxide 419,000 tons
NH3 Anhydrous Ammonia 14,000 tons
PM 2.5 Particulate Matter smaller than 2.5 micrometers 22,000 tons
PM 10 Particulate Matter smaller than 10 micrometers 21,000 tons

These 915,000 tons convert to 1,830,000,000 pounds; a large number to be diluted into the atmosphere in which we all live and manufacture our goods. No wonder the October, 2003 issue of the ASHRAE magazine states on its front cover “Preserving Film, Paper, Electronic Data” which addresses the control of pollutants to minimize such deterioration. Adding these pollutants to natures basics like radiation, moisture, heat (or lack of), vapor pressure and contaminants offers great opportunities to the members of the disicpline in which we all practice.

If removal and/or control of these elements is to take place, we must be prepared to use:
Mechanical Collection devices (filters)
Safe disposal of collected materials
Desiccants and Molecular Sieves
Change of state devices: Heat Exchangers, Refrigeration, Boilers
Scrubbers
Heat Reclaim mechanisms
Exhaust Systems
Fresh outdoor air makeup systems
Space Pressurization
Chemical neutralization
Bio Technology
Incineration

An approach to containment could be to outlaw their creation in any form. The cost-benefit ratio to man of this approach would be so low as to be unacceptable in most cases. The EPA approach is to set maximum allowable dissipation levels at each site, a technique that has a much better cost-benefit ratio and is more palatable by man.

That approach does not eliminate or reduce the need for management of their control in most manufacturing processes. The need in those areas is so great that even the use of outerspace is being researched. Many processes are so sensitive to even infinitessimally small quantities of contaminants that they become not possible without total containment or collection. Certainly the Pharmaceuticals fall in that category but there are others as well.

It seems to us that it is the members of our discipline that have a corner on the selection and application knowledge bank that allows for completion of these complex processes. Should not all of us become major contributors to the increased process sophisticaton and services to mankind?

Engineering Bulletin -Volume 2, Issue #5
by: Kenneth W. Wicks, M.E. – ASHRAE Fellow
and Robert Carpenter – Sales Engineer

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That’s Humidifying

A typical humidification need in the HVAC discipline may require the addition of moisture to maintain a space condition of perhaps 72° and 50% relative humidity when some 2,000 CFM of dry, winter, outdoor air is added to the space.

This results in the need to add some 65 pounds of water per hour using 22 kilowatts of electric power to convert the make up water to steam. The use of city water is acceptable when proper blow down techniques are applied.

A duct handling the 2,000 CFM may have a height of 24″ in which 7 steam distribution tubes on 3″ centers can be installed. This 65 pounds of steam per hour can readily be delivered through the 7 distribution tubes. The absorption into the air stream is rapid and excellent results are obtained.

Now take this same example and apply it to a food processing oven that requires the same 2,000 CFM of cold, dry, outdoor air delivered at 50% relative humidity but the temperature must be 200° and the water must be absolutely pure.

The project now requires some 2,400 pounds per hour of reverse osmosis water delivered to the same 2,000 CFM in the same 24″ high duct. The reverse osmosis system must treat 5 GPM of city water by passing it through a softener, then through odor removing charcoal and finally through several pads of osmosis filtration. The inlet air must be filtered through high efficiency particulate filters.

The pure water is now ready to have its state changed from water to steam, requiring some 800 kilowatts of energy. Such a high level of electrical power is too costly to purchase and is unacceptable to management. Where electrical steam generation was fine for the HVAC application, natural gas becomes the energy choice to make.

The high steam output requirement dictates the use of gas fired units supplying the steam to forty two distribution tubes still in the 24″ duct height and 3″ on center constraints. The forty two tubes would be in six banks of seven tubes each with the banks in series air flow.

An application of this sort requires an ability to respond to the changes of the year round seasons and constant weather front activity. In the HVAC electrical system, the use of SCR control allowed for 100% modulation of the steam generation and full response to changes in load. In the oven process system, the convenience of full SCR modulation is lost and gas turn down ratios become the control method of choice. A 3 to 1 turn down ratio in a single unit is rather insensitive while the 18 to 1 ratio available when three double burner units are used is far more desirable.

The control concern that becomes apparent occurs when the gas fired units have stepped down to the lowest level (150 lbs/hr) and cycle off. It is at this point that a 150 lb/hr humidifier cycles on and is modulated between 150 lbs/hr and zero pounds per hour using the silenium control rectifier. This method allows for predictable control through the wide range from 2,400 pounds/hr to zero pounds per hour.

The need for many distribution tubes in a 24″ duct height requires the use of several rows of seven tubes each in air flow series. Each row of seven can be fed from one generator and excellent response to load change can be obtained.

The fact that preheating of the inlet outdoor air to 200° and humidity sensing at the 200° and 50% level is required must not be ignored.

Obviously this process system requirement is a far cry from the simple HVAC humidification system and concern for the details is most important.

Engineering Bulletin -Volume 2, Issue #4
by: Kenneth W. Wicks, M.E. – ASHRAE Fellow

04-08-03

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Try Optimizing

There is money to be saved!! The selection of system components using optimizing techniques and abandoning the practice of using “Rules of Thumb” will often accomplish meaningful savings with increased system efficiencies.

Most of you have heard of or even practiced:

400 CFM per Ton
Temperature diffusion range should be 20 °
Specify 45 °to 55 ° water
Chilled water is better than DX
No DX below 45 degree° suction temperature
High fin density reduces the number of rows required
Coils throw water above 600 fpm

All often untrue!!!!

400 CFM per Ton -
A properly plotted psychrometric chart will prove that the 400 CFM per ton assumption is only valid when a certain ratio of internal sensible heat load to internal latent heat load exists. Processes that cause moisture to dissipate into the conditioned space result in lower ratios and the CFM per ton is reduced. In addition, higher outdoor air quantities increase the total tonnage while at the same time reduce the required CFM per total ton.

Temperature diffusion range should be 20 ° -
The diffusion range (temperature difference between the room and the air temperature delivered to the room) may be increased and the total CFM required reduced when the air temperature leaving the cooling coil is a close to saturation as possible. The depth of the coil in the direction of air flow determines this approach to saturation.

Specify 45 ° to 55 ° water -
The chilling of water to 45 ° requires more HP per ton than does the chilling of water to say 50 °. The water flow quantity and costs are reduced. Total optimization might reduce the compressor size by as much as one model size. Additional savings are realized when circulating pump, pipe sizes and insulation are reduced and lesser power requirements are present.

Chilled water is better than DX -
The use of chilled water systems in lieu of direct expansion systems is commonly misunderstood. When a common refrigerant supply must serve multiple evaporators, the control and distribution complexities justify the selection of chilled water (or glycol). When only one or two evaporators must be served, the use of a direct expansion system is often justified. The increased efficiency of using only one heat exchange instead of two, the reduced compressor HP requirements and the elimination of circulating pumps can be quite advantageous. The historic claim that DX cannot be easily controlled or modulated has long since been overcome and eliminated as a concern.

No DX below 45 degree° suction temperature -
The use of evaporator temperature regulation has eliminated the concern for freezing of condensate on coil tubes and between coil fins. The optimized use of coil depth and fin density allows for safe use of leaving air temperatures as low as 35° F.

High fin density reduces the number of rows required -
Only in the cases where dehumidification does not occur and condensate does not gather between the fins should high fin densities be used. When the space between fins becomes narrow enough for drops of water to touch an adjacent fin surface, the added capillary attraction increases the quantity of water being held up in the coil. This increased water quantity reduces space for air flow and increases the net air velocity between fins. In addition, it reduces the ability of the coil to transfer heat in those areas that are blocked by water. It becomes apparent that water will be “thrown” into the air stream at lower velocities while static resistance to air flow is increased.
Our tests at the National Bureau of Standards indicated that when the air flow was stopped, twice as much water drained from a 12 fin per inch coil than did from an 8 fin per inch coil after both had been operating under similar psychrometric conditions.

Coils throw water above 600 fpm -
It is false thinking to believe that there is a common air face velocity above which dehumidifying coils will throw water from their face. More critical is the fin density and the face height above the drain pan. A coil with a high face dimension allows more water to run down its fins than does a coil with a lesser face height. The more water that collects between fins means that the water tends to be pushed from the coil face at lower velocities. The shorter the face height and the longer the finned length, the higher the face velocity that can be tolerated. This explains the need for intermediate drain pans.

Engineering Bulletin -Volume 2, Issue #4
by: Kenneth W. Wicks -ASHRAE Fellow
10-07-02

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“AC versus EC”

It seems that most of society thinks of “Environmental Control” as “Air Conditioning”. That is all that one hears around the bridge table or sees in advertising. What a misnomer!

“Air Conditioning” is really a refrigerating process used to keep humans cool enough so that the temperature level around them is satisfactory. We design systems for perhaps 75° F and 50% RH and then control the temperature with a thermostat. This entirely disregards the 50% RH requirement.

We can get away with this because the human body can tolerate rather wide swings in vapor pressure without complaint. Vapor pressure is the pressure at which water molecules bounce off the surfaces in which they are contained. Envision a child’s balloon that has been blown up using human breath. It contains both dry air and water vapor. Each are creating different pressures on the inner surface of the balloon and causing it to change shape. The water molecules bounce off the surface and are either absorbed or adsorbed into any material that is hygroscopic.

Air Conditioning systems normally must deliver rather large quantities of air to the occupied space (perhaps six space changes per hour) versus the lower quantity of new outdoor air required for human occupancy (perhaps 15 CFM per person). This means that only small percentages of outdoor air (10/20 percent) are required. The constant change in seasons and movement of fronts generally is what changes the levels of absolute humidity and dry bulb temperatures. The lower the percentage of outdoor air blended into a system, the less influence it has on the space psychrometrics.

In many procedures, the material being processed is hygroscopic enough to change color, shape, dimensions, odor and/or density. Many manufacturing techniques fail when changes occur resulting in costly rejections. In these instances “Air Conditioning” techniques become inadequate and true “Environmental Control” becomes necessary.

True EC is designed to draw circles of both temperature and absolute humidity for 24 hours a day, year round, on the chart recorder without the saw tooth control that results from component cycling. True modulating control is mandatory.

When large quantities of outdoor air are required, the cooling, heating, dehumidifying and humidifying devices must respond, without cycling, to loads that vary from zero to one hundred percent. This will happen as rapidly as overnight, during which time the refrigeration system must not be allowed to cycle on and off with load variations.

All of this EC requires components that normally do not appear in AC systems. Such items are:
Evaporator temperature modulation
Compressor unloading without shut off
Hot gas bypass
Double suction risers
SCR electric power modulation
Desiccant dehumidification
Humidifier modulation
Multiple compressors
Redundancy
Optimization
Electronic control
Modulating humidistats
Specific air distribution
Special filtration
Corrosion resistance

Let it be said that such systems should be called “Environmental Control” rather than “Air Conditioning”. The attitudes that systems should cost so much per square foot or per ton are obsolete. Such “rules of thumb” must be abandoned.

Engineering Bulletin -Volume 2, Issue #3
by: Kenneth W. Wicks, M.E.
ASHRAE Fellow
8-08-02

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Controlling Clean Room Temperature

 

THE CHALLENGE:

The clean room does not care whether outdoor conditions are cold or warm, damp or dry, clean or dirty, windy or calm. Seasons change, weather fronts roll through, exhaust hoods cycle on and off but production under constant environmental conditions must go on. In order to control a class 1,000 clean room on a 24/7 year round basis at a constant dry bulb temperature of 70 degrees and maintain the relative humidity at 55 degrees is a psychometric challenge of major proportions. Direct expansion refrigeration and indirect gas fired heating will be used as the basis for design.

THE SOLUTION:

High efficiency filtration is used with indirect fired outdoor air heating that feeds treated outdoor air to a modulation direct expansion cooling system. A smaller quantity of treated outdoor air is blended with a much larger recirculating air quantity (320 air changes per hour). A cooling load varying from zero to one hundred percent with an air quantity as low as 125 CFM per ton must be employed. Modulated humidification and reheat are necessary.

A DDC control system must cause the components to respond such that temperature and humidity circles are drawn on the chart recorder. The combination represents true “environmental control” and should not be confused with “air conditioning”. Heating and humidifying must not be allowed to cycle on and off but rather must modulate. In order for direct expansion type cooling to handle widely varying loads and still not cycle off, lowside and highside capacities must remain equal at all times. Carefully selected refrigeration devices are essential. Such sophisticated techniques are required for industrial processes but seldom for the maintenance of human comfort.

Engineering Bulletin -Volume 2, Issue #2
by: Robert Carpenter, Application Engineer
6-18-02

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Electrical Safety

A defogging project in a seafood packing plant brought us in direct contact with a situation where one could not see his hand in front of his face when the lids of the pressure vessels were opened and steam escaped. Production was seriously slowed until the fog abated. Our humidity control system with heated ventilation air and humidistats on the ceiling beams did the job to the owners total satisfaction. At his instruction and to save energy, we were asked to adjust the humidistat set point to a higher level.

In a seafood plant, the floors are usually wet from the washing process. In our presence, the plant maintenance manager ordered an 18 year old helper to go up and reset the humidistats. In order to reach them, he recruited a fork lift operator to raise him up to the beam level after placing an empty pallet across the forks on which he could stand.

The helper carried a drop light with him that he had plugged into a 115 volt wall outlet. While the plant superintendent, maintenance manager and I watched, the operator lifted the helper toward the beam when the wire of the drop light became too short and pulled the light from his grasp. When it hit the cement floor, the bulb shattered.

The lift operator promptly reversed direction and lowered the helper down to the floor. He stepped off the pallet on to the wet floor and proceeded to walk over to the light on the floor. He picked it up, opened the cage and touched the still electrified filament of the bulb while trying to unscrew the bulb from its socket. He was unable to let go and was electrocuted in the seconds it took us to pull the plug from the wall.

OSHA closed the plant the same day and fined the owner for not having trained the new maintenance employee in proper safety practices.

Engineering Bulletin -Volume 2, Issue #1
by: Kenneth W. Wicks – ASHRAE Fellow

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