Comments on: The Problem with Relative Humidity https://www.energyvanguard.com/blog/problem-with-relative-humidity/ Building science knowledge, HVAC design, & fun Sun, 23 May 2021 18:47:28 +0000 hourly 1 https://wordpress.org/?v=6.6.2 By: Matt Risinger https://www.energyvanguard.com/blog/problem-with-relative-humidity/#comment-9009 Sat, 01 Aug 2015 20:42:40 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-problem-with-relative-humidity#comment-9009 Do you have an app rec that
Do you have an app rec that shows these calls given inputs? Great article Allison. Matt

]]> By: David Butler https://www.energyvanguard.com/blog/problem-with-relative-humidity/#comment-9007 Sat, 01 Aug 2015 09:37:57 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-problem-with-relative-humidity#comment-9007 Relative humidity is useful
Relative humidity is useful when discussing indoor moisture because so much of what we worry about (comfort, mold) is specific to the RELATIVE humidity level.

But when we talk about the impacts of ventilation or infiltration, we must use dew point since outdoor temperature is usually different than indoor. Dew point represents the amount of moisture in the air, or absolute humidity.

Thermodynamic wet bulb (TWB) is a different method of measuring moisture, and is only equal to dew point at saturation (100% RH). That means that if you change the temperature of air without removing any moisture, the dew point remains the same but the wet bulb temperature will change. This becomes clear on a psychrometric chart that plots dry bulb, wet bulb, dew point and RH.

Wet bulb was adopted by the HVAC industry decades ago because it was the only moisture metric that could be directly measured, typically with a sling psychrometer. Also, wet bulb is more useful than dew point when sizing a cooling tower or evaporative cooler. Digital RH sensors have made sling psychrometers an artifact of the past, but it persists as a primary reference point in virtually all air conditioning and heat pump performance tables.

]]> By: Andrew L https://www.energyvanguard.com/blog/problem-with-relative-humidity/#comment-9005 Sat, 01 Aug 2015 00:02:37 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-problem-with-relative-humidity#comment-9005 Great article! We really
Great article! We really enjoy reading your posts.

Would you consider writing a blog post on these two topics in the future?

1. Deciding between at on-demand and conventional water heater. Some of the advancements of the newer on-demand units to fix some of the early problems they had with them…example buffer tanks.

2. 1 stage verses 2 stage furnaces. Deciding which AFUE or SEER to go with on HVAC equipment.

3. As a provider, what kind of an effect do you think that States moving to the 2012 IECC will have on the demand for the HERS Index rating? With the blower door being required (unless an amended version is adapted) do you think it will significantly increase the demand for HERS Index ratings or will builders using REScheck just order a blower door individually? Just curious on your take. I imagine as a provider you are working with Raters that are in that situation right now.

As an energy consultant, we get questions about 1 & 2 alot. I’ve done research on them, but I would be interested to hear your take.

Thanks

]]> By: Steve Larson https://www.energyvanguard.com/blog/problem-with-relative-humidity/#comment-9003 Fri, 31 Jul 2015 22:20:58 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-problem-with-relative-humidity#comment-9003 Your story today brings back
Your story today brings back a memory from the early 80s. I was then a firefighter with the Orlando Fire Dept. Management knew the rules applied for their benefit. I decided I needed to know the rules too, so I read the book too. There was a rule regarding outdoor training in Florida’s hot humid climate, when it could happen and when it could not. It used a wet bulb number, and listed how to obtain that number, right in the book. So I learned how to discover how that number was derived. So when they attemted to send us to ladder practice, in full bunker gear, I asked the training staff what the current Wet Bulb number was. They had no one who even knew what a wet bulb number was, let alone how to calculate it, or that it was in the rule book, so we were excused from that day’s activities. I was a favorite guy with my crew, the rest of the guys, and our union. I was not very popular with management, however. But I. Learned that lesson a while ago. They have re-written the rule to make it easier for the training staff, and physical training is now done during the winter months and classroom training is done during the summer. This has probably saved a few lives, thanks to someone learning the wet bulb calculation in 1983…thanks for the memory.

]]> By: Dennis Brachfeld https://www.energyvanguard.com/blog/problem-with-relative-humidity/#comment-9001 Fri, 31 Jul 2015 20:31:27 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-problem-with-relative-humidity#comment-9001 Yes, it is relative, thanks
Yes, it is relative, thanks for reminding us what we should relate too!

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