Wednesday, October 9, 2013

My ASHRAE Journal Articles

I now have 5 of the 6 promised articles published in ASHRAE Journal. The first 4 are posted in the newly redesigned Krueger website under the menu “Learn” > "White Papers" (http://www.krueger-hvac.com/public/learn/white%20papers).

#1 - The first article was about adjusting adjustable diffusers, primarily linear slots (which are seldom adjusted, it seems). In discussions since the publication of this article, I have learned that this is likely a major cause of occupant discomfort in office spaces, as it seems no one ever adjusts them. When slots blow down, they create significant stratification in the space; cold air settles to the floor without very much mixing; hot air rises and the thermostat thinks the room is satisfied, which is true only in a thin layer the same distance above the floor as the sensor. The resultant cold layer causes great discomfort for those occupants not wearing socks; leading to the ubiquitous 1500 watt heater. Perhaps, more importantly, the thermostat response is greatly slowed in this scenario, often 10 times slower than when properly mixed at the ceiling. Adjusting the diffuser then requires that it be rebalanced, which is best done at installation. A combination of instructions from the specifying engineer to the installing contractor is likely the best path to getting this done. 

#2 - The second article was on the tradeoff between energy and comfort. As I reported in my last blog, this one drew comments from a couple energy zealots who, apparently, are still not convinced that making people uncomfortable in order to save energy is counterproductive in terms of both energy and cost. I suspect that anyone who makes a living as an “energy consultant” has misplaced priorities. Worse, there doesn’t seem to be a market for “comfort consultants” to counter them – and there should be, as salaries are on the order of 100x energy costs in most buildings. If we are not careful, we will have buildings that qualify as “Net Zero Satisfaction Buildings (another article I wrote for ASHRAE last year (http://www.krueger-hvac.com/files/white%20papers/article_net_zero_acceptability.pdf).

#3 - The third article was on the validation of high turndown VAV systems, based on recent ASHRAE research conducted on several California buildings. Two significant results (in addition to others) were that loads are so low in a modern office interior zone that spaces are often sub cooled, and that operation at very low air flow rates, with good diffusers (plaque-type, in this case) provide excellent occupant responses. This opens the door for a number of energy saving strategies, including variable volume series fan powered terminal units and fan coils using ECM motors. In both cases, however, maintaining proper code required ventilation rates requires measured and controlled ventilation dampers. There will be an article on this subject in the ASHRAE Journal in the near future from another contributor (who beat me to the punch!).      

#4 - The fourth article was on the issue of area factors for balancing diffusers and discussing why we really can’t publish them anymore, as the choice of the instrument used to measure discharge velocity from a diffuser has become a significant variable in the calculation of the constant to convert velocity to air flow rate. The old stand-by, Alnor Velometer, is seldom used anymore, as the new digital anemometers can store and average data. Sadly, they all respond quite differently to the thin high velocity air jet that is created by today’s air outlets, so there is no single Ak for any device, rather, each device has a different factor. Our advice is to carefully measure the airflow rate for one diffuser/zone on a project and then determine the Ak for that diffuser and velometer.

#5 - The fifth article, which we haven’t yet posted because we haven’t yet received a web-friendly copy back from ASHRAE, is about the lack of validation data on calculations/predictions of a number of building variables, including air motion, energy, and acoustics. The result is that energy predictions often fall far from the mark; spaces are noisy and occupants feel drafts. None of the available building energy programs properly account for the energy consumption of either series or parallel fan powered terminal units, which typically overstates (grossly) the energy use of those with ECM motors. While the savings from variable flow ECM series fan boxes is obvious, one has to “make up” the calculations. Similar issues are found for displacement, underfloor, and chilled beam systems. A literature search will turn up almost no actual energy use data for any of these “energy savings” strategies. Calculation of acoustics for ducted devices is in much better shape, as AHRI 885 has been in place, with a spreadsheet, for a number of years. All that is required is octave band sound power for the devices in question, which has been certified for VAV boxes for many years via the AHRI 880 program. Other ducted devices can be tested to AHRI 260. LEED V4, out this month, will recommend AHRI 885 for proof of compliance with the 40dBA HVAC sound levels prerequisite in classrooms.   

I’ll be working on the 6th article, scheduled for December ASHRAE Journal over the next week. It will either be on water coil calculations for VAV boxes, or on the many “magnification factors” being used to define the performance of inlet probes on VAVC terminals. Stay tuned….

Authored by: Dan Int-Hout, Chief Engineer Krueger