Tuesday, January 31, 2012

What a Load... Room Load, That Is!

I was in Chicago for a week at the ASHRAE winter meeting. One of my tasks, as a member of a Project Monitoring Committee, is to participate in an ASHRAE Research Project (RP). ASHRAE RP 1515 is a comprehensive study of energy and occupant satisfaction at the Yahoo campus in California. The study is being conducted as a joint exercise between Berkeley, Taylor Engineering, and a manufacturer. It should be completed before the San Antonio meeting this summer.

The data so far is very interesting. In both summer and winter (this is California, so it is a mild climate), interior loads are very low. Interior loads are pretty much independent of outside conditions. The system has VAV boxes and plaque diffusers. The assumption (going in) was that at these low loads there was a potential for poor diffuser performance. What was found was the opposite. The plaque diffuser operates well at low flows and there were (little if any) complaints of “dumping” (where cold supply air falls into the space). The complaints came at full flow when the diffusers collided; it was a bit drafty at the mid-point between diffusers.

The real surprise was how low the load in the space was. The design was the “traditional” 1 CFM/SF in the interior, with the boxes set for a 30% minimum, or 0.3 CFM/SF. It was discovered that the boxes were going into reheat at that low flow! They were reset to 10% minimum with a heating setpoint at 50% (per the latest 90.1 addendum on reheat). Analysis after the reset shows that they were averaging about 0.26 CFM/SF in these interior spaces. I assume that, being Yahoo, these spaces had at least a full complement of computers in the work stations, and likely dual monitors. Yet the loads were very low.

This confirms what I have been seeing for some time. The DuPage City courthouse, that I was an observer for back in 1991, had an interior load of 0.4 CFM/SF and had issues with diffuser performance at these low loads. Nonetheless, we are seeing designs based on much higher loads. 0.5 CFM/SF is about 11 BTUH/SF with 55ºF supply air. The Yahoo buildings are likely close to 4 BTUH/SF in the interior spaces. The load is also pretty well matched to the minimum ventilation rate.

It is apparent that we need to reevaluate the way we are calculating loads and operating buildings with these low loads. Humidity control, minimum ventilation rates, and minimum effective control for VAV boxes are all tied together. The same is true for other systems, especially chilled beams. At low loads, an oversized chilled beam (which reduces first costs) is just a very expensive diffuser. The same is true for VRV, fan coil and displacement ventilation systems. Failure to understand what is happening in today’s offices can result in wasted energy as all these systems start to go into reheat to maintain acceptable space temperatures. What a load!

Authored by: Dan Int-Hout, Chief Engineer Krueger

Thursday, January 26, 2012

40 FPM, Round 2

As I mentioned in the previous blog, there is an issue with a limit of 40 fpm in the occupied zone, a limit which is likely to always be exceeded somewhere. I proposed the following to the TC 5.3 (Space Air Distribution) handbook committee last week at ASHRAE. It was determined that it belongs in the Applications Handbook, which is a couple years away before needing revision.

We presented it to the Standard 55 committee, which determined it to be inappropriate to include in the Standard, but would be useful in the upcoming Design Guide (as yet unfunded). So, I’m posting it here for comments. I have sent it to the LEED IE TAC for inclusion in the LEED 2012 reference guide, now being put together. (Send comments to dint-hout@Krueger-hvac.com.)

Proposed prescriptive compliance path for overhead, well-mixed air distribution, at the design stage.

6.2.1 At a minimum, for compliance to ASHRAE Standard 55 requirements in Section 6.2, when using an overhead (well-mixed) air distribution system in an office environment, the following shall be considered a set of minimum design considerations:

6.2.1.1 An interior space with multiple diffusers shall be selected so that in cooling mode, the calculated Air Diffusion Performance Index, based on table 6, ASHRAE Fundamentals, Chapter 20, is at least 80% at all expected loads and flow rates. Achieving this requirement allows the designer to assume average room air speeds are less than 40 fpm, the room environment is thermally uniform, and the graphical or PMV methods of determining room setpoints may be allowed. It also assures compliance to the maximum room air stratification limit of 5.4F in the occupied zone.

6.2.1.2 In addition to the requirements of 6.2.1.1, an interior space in heating mode shall be supplied by a room to discharge temperature differential of no greater than 15F. This assures compliance to the maximum room air stratification limit of 5.4F in the occupied zone.

6.2.1.3 A perimeter space in heating mode shall be supplied with diffusers that result in the 150FPM throw making it to within 4.5ft of the floor along the perimeter wall, and having a room to discharge temperature differential of no greater than 15F. This assures compliance to the maximum room air stratification limit of 5.4F in the occupied zone.

6.2.1.4 A perimeter space in cooling mode with both perimeter and interior diffusers, such as an open office space, shall have a calculated ADPI for the collision zone between perimeter and interior diffusers of at least 80%, assuring no objectional drafts will be experienced by the occupants.

6.2.1.5 All diffusers shall be located so as to avoid obstructions that would cause the discharge jet from the diffuser being directed into the occupied space. This assures that no excessive air speeds will be encountered by the occupants, which would void the use of the PMV or Graphical methods to determine a proper room setpoint.

Authored by: Dan Int-Hout, Chief Engineer Krueger

Friday, January 13, 2012

The 40 FPM Quandry

We, as well as some of our competitors, have had engineers call and ask if we can guarantee that our air distribution system can guarantee to achieve less than 40 fpm at all points in the occupied zone, in order to meet LEED thermal comfort requirements. The fact is that no overhead system can guarantee meeting this requirement. The requirement comes from a statement in ASHRAE Standard 55 that the Graphical Method, "Figure 5.2.1.1 specifies the comfort zone for environments that meet the above criteria and where the air speeds are not greater than 0.20 m/s (40 ft/min)." The graphical method is the most used method in the standard, as it is the easiest.

In another section of the 55 Standard; however, it states "the designer shall decide the proper averaging for air speed for use in the Graphical Method (5.2.3.1)". One method (in fact the only method) of estimating room air speeds is to use the ADPI methodology described in the ASHRAE Fundamentals Handbook, chapter 20. If the ADPI is calculated to be at least 80%, the average room air speed can be assured to be less than 40fpm. In fact, it is usually no higher than 30 fpm. This relationship will be included in an addition to the Handbook in the near future.

In addition, an ADPI >80% will also assure that there is less than the maximum 5.4F vertical temperature stratification in the occupied zone, another Standard 55 requirement. Thus, if the engineer chooses to use ADPI as the method of estimating air speed, he will be allowed to use the graphical method of determining design temperatures and assuring compliance to the stratification requirement as well.

Krueger has the best, and easiest, ADPI selection methods in the industry, including ADPI selection graphs in the catalog and an easy to use ADPI calculator and printable graph output in K-Select. We also provide the only available Standard 55 Graphical Method computer program as a free download on our website. (http://www.krueger-hvac.com/tools/comfort.asp)

Authored by: Dan Int-Hout, Chief Engineer Krueger

Monday, January 9, 2012

Top 10 Predictions for 2012

1. LEED 2012 will be released in the fall, and it will result in a number of changes in the way building HVAC systems are designed, both for energy savings and acoustics.

2. The ASA Classroom acoustics recommendation (essentially NC=26, ANSI 12.60) will become a default requirement for new classroom design. The LEED prerequisite will require that either the ASHRAE handbook, or AHRI 885 will be designated as a primary method of estimating sound levels in schools and other places as well; engineers will discover that the 885 spreadsheet is a much easier approach.

3. ASHRAE Thermal Comfort Standard (55-2010) will include mandatory language only for the calculations employed. A set of default compliance paths will be developed and put out for public review.

4. The updated ASHRAE UFAD Design Guide will come out of committee at the summer meeting.

5. Displacement Ventilation will continue to see significant use in classrooms, due to its low sound generation.

6. Chilled Beams will continue to be used by innovative engineers. While I hope to see some validation of the energy consumption savings, I predict we won’t.

7. BOMA will continue to state that the number 1 reason for not renewing the lease in high rise buildings is “occupant dissatisfaction with the building environment” (ie: comfort). I still see new designs with designed discharge temperatures for overhead systems in excess of 100°F, which leads to significant stratification.

8. The market for HVAC components will again be relatively flat with local ups and downs.

9. VAV overhead air distribution will continue to be (by far) the most used system in new buildings. ADPI will be endorsed by the ASHRAE Fundamentals as a method of predicting both thermal uniformity (complying with the vertical stratification requirement of standard 55), and that the average room air speed is less than 40fpm, allowing the graphical and PMV calculations of Standard 55.

10. Sadly, the Cowboys will continue to disappoint their fans.

Authored by: Dan Int-Hout, Chief Engineer Krueger

Tuesday, January 3, 2012

2011 Prediction Recap

It’s time for the 2011 recap. So how did I do with my January 2011 top 10 predictions?

1. LEED 2012 will be approved, pretty much as it is in its first public review.
Final public review will be out in a couple of months. I give this a 9 score.

2. The ASA Classroom acoustics recommendation (essentially NC=26, ANSI 12.60) will become a requirement in many local codes and may be a part of the next IBC. It will also be a requirement of the ADA governing bodies, forcing a redesign of many school HVAC systems.
Still on track. AHRI 885 is designated as a primary method of estimating sound levels in schools and other places as well, in LEED 2012. I give this a 9 score.

3. Over my objections, the ASHRAE Thermal Comfort Standard (55-2010) will be rewritten into code language. I predict this will result in gross misuse and misinterpretation of the requirements and will make lots of money for trial lawyers. (I hope I’m wrong on this one.)
The Standard is being revised (by addenda) to make calculations mandatory, with an informative appendix containing recommendations. I give this a 5 score.

4. With any luck, we will get a rewritten ASHRAE UFAD Design Guide out of committee at the summer meeting. The current manual has been pulled from the ASHRAE bookstore following complaints, most noticeably from the GSA, over lack of discussion of the potential negative issues with this design concept.
Final first draft has been posted and is hoped to be voted on in Chicago. I give this a score of 8.

5. Displacement Ventilation will see significant use in classrooms (it’s quiet, see item #2 above).
This trend continues. This is a 10.

6. Chilled Beams will continue to be the “darling” of innovative engineers. We will not see validation of the calculated energy savings from this relatively new technology. That will not, however, prevent estimates of significant energy savings, resulting in LEED points.
Still no peer reviewed data on energy savings with this technology. Developing AHRI and ASHRAE test methods should put to rest some unfounded performance claims. This is a 10.

7. For the umpteenth year in a row, BOMA will state that the number 1 reason for not renewing the lease in high rise buildings is “occupant dissatisfaction with the building environment” (ie: comfort). See item #3 above.
BOMA confirms that 2010 was another year in which occupants are not happy with their environment. This gets a 10.

8. The market for HVAC components will continue to be relatively flat with local ups and downs.
Pricing was a challenge in 2011, and will continue in 2012. I give this a 10.

9. VAV overhead air distribution will continue to be (by far) the most used system in new buildings.
Most designs continue with the tried and true overhead VAV designs. This is a 10.

10. The Cowboys will continue to disappoint their fans.
Fortunately, we won’t have to watch them for another 6 months. I give this a BIG 10.

Total score: 91. (out of a possible 100).

Let’s see if I can do as well in my predictions for 2012. Top 10 for 2012 next week!

Authored by: Dan Int-Hout, Chief Engineer Krueger