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Humidification Rules Of Thumb

2011-07-08T08:35:00.000-04:00

Every industry has it's share of "rules of thumb". If you're involved in the air conditioning & refrigeration industry you probably associate 400 cubic feet of air per minute as the airflow required per ton of cooling. If you are in the gas combustion industry you may use 1000 BTU per cubic foot as a rule-of-thumb for the calorific value of natural gas. These numbers or "rules" are used by you in many of your day-to-day calculations as you size equipment, estimate loads, or bid equipment.

When dealing with humidification products, there are some rules of thumb that we would like to discuss with you. These "rules" could be a number, a dollar value, or just about anything. In no particular order, here are some from our list...

---> For each pound of water that is evaporated, 1000 BTU's of heat are taken from the air. This is that evaporative cooling effect that you may have heard about. Latent heat... etc... etc...

---> Electric steam humidifiers consume 333 Watts of energy per pound of steam generated. This number will vary slightly from manufacturer to manufacturer, but this is the number we use.

---> A 1°F temperature change can result in a 2-3% swing in relative humidity.

---> Each 100 pounds of steam generated by an electric steam generator cost $4.00. Of course, this number can vary depending on electrical cost, but this is a good starting place.

---> The maximum absolute humidity doubles for every 20 °F increase in temperature. Thus, the relative humidity will drop by a factor of 2 for each 20 °F increase in temperature.

Keep in mind, these are "rules of thumb". They are not exact and shouldn't be used in calculations that require superb precision. They should help provide quick perspective the next time you need to quickly calculate an energy cost or estimate the cooling effect for an evaporative system.

Basic Load Calculation

2011-06-17T09:33:00.000-04:00

Calculating a humidification load can range from simple to very complex... depending on the application. One very common application involves replacing moisture that is exhausted from the space due to ventilation requirements for IAQ. An air handling unit introducing outside air is usually installed in a situation like this. A certain amount of the total airflow through the air handler will be coming from outside. During the heating season, the outside air can be very dry so the affect on the humidity in the space is negative. This post will help you understand how ventilation rate, sensible heating, and humidification relate. A more comprehensive explanation of the load calculation with real life examples and THE MATH can be found by downloading and reading our Load Calculation Guide.

Our example building will be fairly small. It is a 5000 sqare foot office space. It has a single air handler that moves 3000 CFM. The unit introduces 20% outside air so we will have to add humidity in the winter to maintain the design condition of 72F and 40% relative humidity. Basically, we have 2400 CFM of air being recirculated and 600 CFM of outside air being added from outside. The way this works is below...

2400 CFM of air at 72F & 40% relative humidity
600 CFM of outside air at 0F & 50% relative humidity

This mixes and we arrive at this point...

3000 CFM of air at 57.6 F & 53.6% relative humidity

Obviously this air is too cold to introduce to the space during the heating season... so... we heat it.
Add 47,000 BTU's and we arrive at...

3000 CFM of air at 72F & 32.5% relative humidity

We want to humidify this air now to arrive at the design condition listed above.

If we add 17 pounds per hour we arrive at 72F & 40% relative humidity.

This is not meant to be an actual load calcuation. Many things have been assumed and others not considered at all. This is simply an example to illustrate the main points... ventilation, heating, and humidification. The Load Calcuation Guide availble in the resources section of website will shed additional light on how you can accomplish calculating actual loads for real life situations.

Herrdraulic High-pressure Humidification Systems

2011-06-01T14:07:00.000-04:00

Electric steam humidifiers are very common-place in today's market. They are simple, easy to implement, and just work. Why would any engineer consider using something else? The downside... they can be energy hogs.

If your application needs greater than 100 pounds per hour of humidification capacity, check your electric bill. An electric steam generator operating at 208 volts (3 phase) will draw over 90 amps. Electrical rates continue to rise, so engineers are being more careful by designing systems with energy conservation in mind.

Atomizing systems utilize heat already present in the air to evaporate the water into the airstream. Thus, there is no need for electrodes or heating elements. The result is a much lower electrical cost. In some cases, 100 times less. An electric steam generator can cost more than $4.00 to generate 100 pounds of steam per hour. An atomizing system (depending on the type) can generate the same capacity for only pennies.

The Herrmidifier Herrdraulic High-Pressure Humidification System utilizes an oil-free, stainless steel axial-piston pump to generate 1000 psi water. This high pressure is used to force water through tiny nozzles resulting in extremely fine, quick-evaporating particles of water. The variable speed pump and multi-stage valve plate allows for an increased turndown ratio; which allows for precise control of the humidity levels.

Remember, as your capacity needs increase, multiple electric units will cost you in the long run. An atomizing solution will conserve energy and keep your ongoing costs lower. Find out more about the Herrdraulic system by clicking over to the products section.

Authored by Steve Schneider, Herrmidifier Product Manager