Monday, October 31, 2011

People Still Don't Get It!!

I spent last week in Boston calling on engineers with our rep there. As I always do, I asked the question “What does ASHRAE recommend as the maximum delta-t between room and discharge, when heating from the ceiling?” Out of 60 engineers in 7 engineering offices, only one individual knew the answer. Sadly, this has been the pattern for as long as I have been asking the question.

The answer is, of course, 15 degrees-F. Discharges greater than 90F in a 75F room (87 in a 72F room) are going to result in significant temperature stratification in the room. ASHRAE Standard 62.1 requires that when this delta-t is exceeded, the system must increase the minimum ventilation air to the space to account for the inevitable loss of ventilation to the room due to short circuiting into the return air plenum. In Mass., as in many states, this is code, as the Ventilation Rate Procedure of 62.1 is referenced in the 2009 International Mechanical Code, which has been adopted by the state.

More importantly, ASHRAE Standard 55 (Occupant Comfort) cannot be met with high discharge temperatures. The 55 Standard only allows 5.4F vertical temperature difference between 6in and 6ft. I have never witnessed a test where this requirement was met with greater than 15 degree supply-room differentials, and I have conducted over a thousand such tests over the past 35 years.

While not code, ASHRAE 55 should be a concern to everyone. Occupant salaries in many buildings are at least $200/square foot/year. A building that uses more than $2/square foot/year in energy is a poor performer. BOMA has continually stated that the number one reason for not renewing the lease in a high rise office building is “occupant dissatisfaction with the environment”. Considering how few engineers apparently understand the very basic idea that hot air rises, I suppose this is not surprising. We continue to see VAV box schedules with design discharge temperatures in excess of 120F.

I will continue to pound on “the rules” as I call on engineers around the country. The ASHRAE Journal article on overhead heating was recently reposted as a link in the HVAC news weekly e-mail, and a version can be found at http://www.krueger-hvac.com/lit/pdf/white_AJ_reheat.pdf.

Authored by: Dan Int-Hout, Chief Engineer Krueger

Friday, October 21, 2011

ASHRAE 113 & Standard 55

It has come to my attention that a number of engineers are requiring the use of ASHRAE Standard 113 to verify compliance to ASHRAE Standard 55. That is not likely to be a successful venture, as the 113 Standard is really intended as a laboratory method of test.

I was the original author of Standard 113, back in 1979. It was originally an appendix to an ASHRAE Technical paper on how to get repeatable measurements of room air motion in an office space mock up, written to prove compliance, or in this case, non-compliance, to a GSA specification. The tests conducted under the protocol which became Standard 113 proved that in fact it was not possible to meet the GSA specification with any air distribution system. The GSA subsequently modified the specification, and shortly after dropped the requirement entirely. It also proved that getting repeatable results required very expensive instrumentation, modifications to the controls of the space being measured, and the addition of simulated loads to maintain the steady-state conditions required for the measurements, which often took an hour or more. For a number of reasons, it is unlikely that one can conduct a true ASHRAE 113 test in an office space.

I was Chair of ASHRAE 55 Standards committee when the 2004 standard was released. Compliance paths have always been a goal, but have never been fully or properly defined, due to the inherent difficulties in measuring the highly variable and often non-steady state conditions that exist outside of laboratories. We are still working towards that end and are developing compliance paths for different types of air delivery systems. That is still a work in progress. They will not, however, include a requirement to conduct air distribution tests per ASHRAE 113.

The relationship between measures of room air motion and Standard 55 are not clearly spelled out in the literature. ADPI (Air Diffusion Performance Index) can be predicted from manufacturer’s throw data and an analysis of diffuser spacing from tables in Chapter 20 of the ASHRAE Fundamental’s Handbook. ASHRAE 113 data can, and has been used to calculate an ADPI under steady-state conditions. An ADPI of 80% or greater will ensure that there is less than the ASHRAE 55 vertical temperature stratification limit of 5.4 degrees F in the lower 6 feet of a space. That is only a small part of the Standard 55 requirements, however.

The likely steps to prove compliance to Standard 55 will involve temperature difference measurements only, as these are much more stable than velocity measurements, and can easily be taken in occupied spaces. Air speed measurements are so highly affected by local loads that any measures are unlikely to be repeatable or meaningful, in practice. There may be some meaningful data obtained at the midpoint between diffusers to look for jet collisions at high air flow rates, or under diffusers at low air flows looking for excessive drop (dumping). These would involve some visualization and single point measurements, a type of measurement not included in ASHRAE 113.

In short, the only practical way to place ASHRAE 113 in a specification is to require its use in a full scale mockup to verify the predicted ADPI from the ASHRAE handbook table calculations. This will likely be a very expensive test and should not be employed except for very large projects where the cost might be justified.

Authored by: Dan Int-Hout, Chief Engineer Krueger

Monday, October 10, 2011

Post Greenbuild Show

I spent last week in Toronto at the Greenbuild Product Show and Conference. We had a product booth again this year and showed examples of our Chilled Beam, Displacement, and Underfloor products, which are widely considered to be “green” products. In reality, of course, everything we make can be utilized in a “green” application. It’s all in the way they are used, of course. Once again, the product show was largely related to non-HVAC products, as it focuses on building materials and green software vendors.

I presented my portion of the panel talk “Can we have our cake and eat it too? Balancing Energy Efficiency and Occupant Comfort ” The room was packed with over 250 attendees. My portion was to present the history of bad decisions made in the name of energy conservation that resulted in poor occupant comfort (and no energy savings). The others on the panel discussed how we are getting occupant feedback on new projects, and proved that one can actually save energy with comfortable spaces. There were a number of interesting questions asked, and I believe we covered the subject well.

If you have been following my blog, you will know that I was concerned that the USGBC is putting Global Warming and energy use ahead of occupant needs, in their hierarchy of importance. Fortunately, I think we have convinced the Energy folks enough that they have finally agreed to increase the weighting for issues regarding comfort!

Authored by: Dan Int-Hout, Chief Engineer Krueger