BMS reConnect #43: VAV Box Temperature Stratification Problems
Also, a newsletter update, an Olympic suggestion, upcoming ASHRAE event, etc.
UPDATE
I try to be pretty disciplined in getting at least one of these out a month for the past few years. July was one of the first misses I’ve had since I started this. There’s been a lot going on behind the scenes, but I’m still not happy to have a miss. I will do better.
So the update to share is that the newsletter is in a bit of a transitional period. There may be a few more missed months along the way, but I intend to continue keeping the course while a few behind the scenes things shake out. Stay tuned for what comes next from your favorite intermittent internet publication at the nexus of building controls, energy performance, professional darts, and Z-list news. Cheers!
THE OLYMPICS
I’ll admit I wasn’t really feeling the Olympic Spirit a few weeks ago leading into the 33rd modern summer games in Paris, but I’ve come around. The family has been into the gymnastics and swimming, I’m pretty interested to watch some of the wrestling (starts in earnest today), and damn…did you see the finish to that steeplechase race the other day? Where the guy was making a move to land on the podium, clipped the last hurdle, fell, and got KO’d? Crazy! Hope that guy is okay.
But now I get to the main point: why on earth are DARTS not an Olympic sport? We’ve got badminton, table tennis, 3-on-3 basketball (WTF?), and—apparently, as I have just learned—breakdancing. There must be room for darts in this mix!
Besides…it would be good to give the Brits a few more opportunities to medal. Can’t you picture the scene with these finely tuned athletes on the podium of the world stage? I can:
VAV BOX TEMPERATURE STRATIFICATION
I had missed this article a few months ago, and it was quite a miss. Excellent read for anybody that is interested in matters of temperature control in variable air volume (VAV) box systems, especially in northern climates. My LinkedIn algorithm served this up again from 10 months ago, and I was glad it did.
Appearing in “Engineered Systems” in August 2023 by author Francisco Valentine, PE, “A Design Solution to Improve Heating Performance of Pressure-Independent Terminal Units” highlights a more-common-than-you’d-think problem in many pressure independent VAV systems: significant temperature stratification in rooms with exterior exposures such that temperatures near the floor and the temperatures near the ceiling can have up to a 30F delta. The study suggests inadequate throw from the registers at low flow conditions which leads to the clouding of warm air near the ceiling, preventing a thorough mixing of supply air with the room air. The issue is illustrated here, where air throw in cooling mode (under high flow conditions) adequately reaches the occupied zone, while air throw in heating mode (lower flow) never makes it to where the people are. That is a problem.
As it were, installing the same diffuser at every register does not take these concerns into consideration. The proposed solution to this is the incorporation of airflow control/diverting dampers coupled with more appropriately selected diffusers. In a nut shell, perimeter diffusers should be selected for heating mode performance:
The combination of more appropriately selected diffusers (identified at design stage with heating performance in mind) with a control strategy that forces more air to those diffusers when needed should yield a better mix of supply air and room air, leading to improved comfort in the occupied zone. Like this:
The article also provides an excellent all around overview of VAV systems for anybody new to the field or looking to learn a bit more. Highly recommended!
MEMES
This one made me think:
INDUSTRY EVENTS
Just came across a future event that looks excellent:
The technical agenda is here, with a few session highlights I will call out:
Lessons from New York City’s Building Decarbonization Policies for Other Global Cities
Decarbonization in Action: Metrics That Matter to CRE Portfolios
Lessons Learned from the Trenches: Delivering Resource-Efficient Decarbonization of Tall Buildings in NYC
Building Blocks of Thermal Energy Networks: Sharing Heat Between Neighboring Tall Buildings
Keeping Decarbonization Cool: Future of Refrigerants in Commercial Building HVAC Systems
Check Your Assumptions: How Our Defaults are Derailing Decarbonization
The Power of Partial: Electrification Strategies in Cold Climates
A lot of really good sessions here (with some friends speaking in a few). Kudos to ASHRAE for keeping up with the evolving policy landscape by putting this conference together. Love it or hate it, this decarbonization stuff is coming…great to have a resource like this available.
ACOUSTIC JAMS
Southern Cross has long been a favorite song of mine. I wanted to learn a bit more about its songwriting process and was surprised to learn it was not written by Stephen Stills, but rather re-written by him. Per the Wiki entry:
"Southern Cross" is based on the song "Seven League Boots" by Rick and Michael Curtis. Stills explained, "The Curtis Brothers brought a wonderful song called 'Seven League Boots,' but it drifted around too much. I rewrote a new set of words and added a different chorus, a story about a long boat trip I took after my divorce. It's about using the power of the universe to heal your wounds. Once again, I was given somebody's gem and cut and polished it."
Here’s the original, followed by the CSN classic. Enjoy!