Humidification and Dew point control
Humidification and Dew point control
(OP)
I have been asked to look at conditioning a number of large rooms and also to humidify tham.
The rooms need 100% fresh air (Smoking areas--night club/casino etc)
The airflow rates are varied but I have four plants in excess of 12m3/sec.(one is nearer 17m3/sec)
What is the best way to humidy these areas. I guess spray washer (Electric hum will be massive)
If spray washer, is dew point control easy to implement and do i need a special 'dew point' sensor or is this simply a standard dry bulb sensor?
The rooms need 100% fresh air (Smoking areas--night club/casino etc)
The airflow rates are varied but I have four plants in excess of 12m3/sec.(one is nearer 17m3/sec)
What is the best way to humidy these areas. I guess spray washer (Electric hum will be massive)
If spray washer, is dew point control easy to implement and do i need a special 'dew point' sensor or is this simply a standard dry bulb sensor?
Friar Tuck of Sherwood





RE: Humidification and Dew point control
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Spray wash is probably a good choice. It would have the possible side benefit of removing some of the smoke and allowing you to use less that 100% OA.
RE: Humidification and Dew point control
what are your oudoor air design conditions?
RE: Humidification and Dew point control
PS Dew point control...is it easy to achieve or am i complicating things. What about gas fired humidifiers?
Friar Tuck of Sherwood
RE: Humidification and Dew point control
Anything that adds humidity via steam also adds sensible load which needs to be countered by the refrigeration system. Kind of an energy pig.
RE: Humidification and Dew point control
I recommend that you obtain some input from a trusted BMS contractor at the design stage; the control system could make or break such a project.
RE: Humidification and Dew point control
I would advise plotting the process on a psychrometric chart and see how much extra moisture addition is required. I don't have a Psychrometric chart at hand now but I feel the summer conditions can be maintained by just cooling down the air and thus increasing RH. Air, in winter condition, to be heated up first and then moisture added for efficient process.
I feel a humidistat is just fine and can control within an accuracy of +/-2%.
What are the required room conditions?
Regards,
RE: Humidification and Dew point control
RE: Humidification and Dew point control
I was thinking if I used a spray type washer that the process follows the wet bulb line and would therefore reduce the chiller load.
If you consider air at -8C outside, this could be heated to say 21C, then spray washed which would cool it and humidify it (Saving energy, since I would need compressed air to atomise the water and not steam from an electric source or stean boiler plant)
When you use a system like this, you have to try and get the right spray washer 'off coil' conditions by varying the pre-heat and washer spray rate (I think thats how you do it anyway).
Its HOW you actually measure the off coil which gives it it's name 'dew point control'. I always thought a standard dry bulb sensor was used in the ahu for this purpose, but a humidity sensor was used as a limit device to stop over humidification (in both the supply duct (and one in the room for final control??)
Friar Tuck of Sherwood
RE: Humidification and Dew point control
With 28C and 50% inlet conditions, 22C and 50% can't be acheived with humidifaction alone. You can land up near 22C and 60 to 65%RH, which seems to be good. What you plan for winter condition is perfect. Just preheat it and then air wash it.
When we deal with AHUs, DP at coil is always maintained constant and so you can control the required parameters with only DBT. I would rather go with a DBT for reheat and then an RH sensor for humidity control.
www.armstrong-intl.com provides you an excellent and free handbook + selection software for humidifiers if you register.
Regards,
RE: Humidification and Dew point control
RE: Humidification and Dew point control
Humidifiers using the adiabatic process exchange sensible heat of air with the latent heat of water to accomplish evaporation. The result is a drop in air temperature while the total heat (enthalpy) remains the same. In other words, moisture is added to the air at the expense (or benefit) of a drop in air temperature.
Representing the adiabatic group in this comparison is the ultrasonic atomizing humidifier. This system generates a fine mist through high-frequency vibration of an electrically powered transducer. It was selected because of its very high operating efficiency. Recent models have demonstrated atomization of water droplets down to 1 micron, which improves absorption capability. The U.S. Department of Energy published a Federal Technology Alert on these systems, which can be obtained at (www.eren.doe.gov/femp/prodtech).
The total read is at http://w
RE: Humidification and Dew point control
HVAC68
RE: Humidification and Dew point control
RE: Humidification and Dew point control
RE: Humidification and Dew point control
RE: Humidification and Dew point control
Issue 1 is that I'm skeptical of the need for a 50% RH during winter. In summer, it's okay to ask for such a dehumdification value from your air handlers if the duty calls, but a 50% RH in winter in the UK and many northern sectors feels like Pea Soup. You might not realize this until you walk into the space from the non-humidified, surrouding 69°F, 10% RH space. To me, it's ludicrous to ask this of a high volume make-up air systems serving cocktail lounges...
Let's re-check the needs first, hopefully from an authority who understands the psych chart. If you're asked to do something nuts from the client, talk them in off the balcony before obliging.
-CB