CIET's Ask Us Anything series is a free monthly Q&A session with industry experts.
The Better Building Operations session featured Michel Parent, CIET Trainer and CMVP Expert.
If you missed this Ask Us Anything, here is a key topic that was discussed during the session.
First thing first. I've been asked sometimes: what is a more efficient humidifier? There's no such thing.
Humidifiers have to boil water in some form and that will always cost the same amount, or take the same amount of kWh or Btus. Obviously, if it's gas, you have an efficient, whereas if it's electric, it's 100% efficient.
The best practice when you look at minimizing or optimizing your humidification - we're talking about making sure your sensors are correct; that your set points are realistic; and if you use outside air economizer, realize that it will cost you in humidity costs. So if you have the possibility of using a water side economizer, rather than an air side economizer, it will significantly reduce your humidification cost.
The more outside air you bring in in the winter, the more humidity you have to input into your airstream, so the more costly. So when we're dealing with minimizing humidification cost, proper sensors, calibration is critical. Proper set points that are not too high - you might have heard that during the pandemic you should maintain 40-60%. I would invite you to be very careful about that. It has a lot of building envelope issues if you do this, in many cases.
Public Health Ontario actually published a position paper not too long ago where they say that there is no proof that 40-60% relative humidity in the building has any impact on pandemic- or COVID-related questions. So I would say: make sure you select a set point that is sustained without condensation. Then make sure your sensors are properly calibrated.
When you do dehumidification, it's the same thing. When you dehumidify, it will be done through your cooling system. So you won't necessarily save by changing how you humidify. It's really the set points, and the sensor you're using. If you dehumidify, that's usually limited to a few types of buildings where active dehumidification is present. You've tried to reuse the condenser heat to reheat. When you dehumidify, you have to subcool the air, which means it's too cold to send into the building. You could reheat that air because you need to reheat it with natural gas or electricity; it's very wasteful.
If you have a DX system or any type of heat recovery chiller or anything like that, when you need to reheat your air, as much as possible, use condenser heat, which would recirculate, which would actually recycle the heat that you use to dehumidify.
That's one thing where you have to be very careful about dehumidification: trying to reuse that heat that has been rejected from the dehumidification process
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