Wednesday, September 3, 2014

Engineers Push Back

I recently received a nice letter from an engineer in California who said she had heard me speak a few years ago about overhead heating and had been following my advice (and that in 62.1 and the Handbook) about limiting discharge delta-t to 15oF. She then went on to say how surprised she has been at the push back from engineers on this recommendation. Sadly, I had to tell her that my experience has been similar.

In my role as an ASHRAE Distinguished Lecturer and in making engineering sales calls with Krueger Reps, I see an average of 1000 engineers a year. I almost always manage to bring this topic up in conversations or lectures and nearly every time, there’s an engineer that tells me, “I’ve been doing this for XX years and no one has complained”.

Apparently, the concept of hot air rising (and cold air falling) isn’t a universally accepted paradigm when it comes to air distribution. This person (California engineer) mentioned that there is disbelief in my stated rule on heating a room, where “the hotter the air delivered at the ceiling, the longer it takes to heat a room.” Sorry folks, but it’s true - overly hot air dispensed at the ceiling will most certainly want to stick to it. The hotter it is, the longer it will stay stratified, which means the longer it will take to cool enough to blend with the air below in the occupant space.

Every forced air project with a heating coil likely has an equipment schedule. Somewhere on that schedule is a column headed ‘Leaving Air Temperature’. If any values in that column are 15°F greater than the designed zone temperature (usually between 73°F and 75°F), the code official has the right to ask how the engineer intends to comply with the Standard 62.1 requirement for increased ventilation air and if that requirement was included in the building load calculations. If you recall, ASHRAE Standard 62.1 requires an additional 20% outside air if heating from the ceiling with a ceiling return, as is the case in most commercial buildings. The 62.1 Ventilation Rate Procedure has been adopted by many, if not most building codes.

It’s also worth noting that any space with a discharge to room differential exceeding 15°F will not comply with the vertical stratification limitation of ASHRAE Standard 55, which is often included in many codes, if not a minimum in building design assumptions. Still, engineers are pushing back. It’s no wonder the level of discomfort in commercial spaces is as high as it is. But as they say, “who’s checking?”

Do you work in a stuffy building? Are you using a space heater year round? Tweet us @KruegerHVAC and share your comments with the HVAC engineering community. Let them know that regardless of #whoschecking, proper air distribution matters.

Authored by: Dan Int-Hout, Chief Engineer Krueger

Tuesday, July 22, 2014

Air Leakage

Not too long ago, I attended my first ASHRAE meeting as a member of the Board of Directors. My time at the meetings has, for the most part, been focused around participating in the Tech Council and being a board representative on RAC (at least for one year). It’s a busy job, but someone has to do it!

As for recent happenings, I have received quite a few questions about air leakage. Ironically, there has also been a push from the 90.1 committee for VAV box manufacturers to “come clean” about air leakage rates. Just to give some history, a couple years ago the AHRI section that covers VAV terminals was asked to come up with leakage numbers. Several manufacturers put numbers on the table for single duct and dual duct boxes, as a function of size and type of heat. This data was presented to those requesting it. They then asked, “So when will you start certifying the data?” The answer is never. Not only is the required test setup expensive to run, but there are a number of uncertainties involved. With regard to cost, if for some reason a test failed to be certified, the penalties are so expensive that it would most certainly warrant an increase in cost, which we know would not be received well by customers. (Then, to make matters worse, there is little payback for the slight reduction in leakage that would result for single or double duct units.) So, when we informed the interested parties that there would not be a certification program, their response – to our surprise – was “then, never mind”. However, there have been rumors that the DOE is pushing the 90.1 committee to bring it up again.

Fan boxes, on the other hand, are a different matter. For starters, a both series and parallel fan boxes, for the most part, are under negative pressure, so leaks would be in the unit, not out. This is definitely the case for series boxes. For parallel boxes, half the unit is at a slight positive pressure, but it is probably no more than 0.5”, which is just enough to feed the downstream diffusers and ductwork, and possibly a water coil. The backdraft damper on parallel boxes, however, is seldom robust enough to effectively provide a tight seal. The ASHRAE/AHRI project evaluating series and parallel boxes at Texas A&M University found that a typical parallel box will leak between 10% and 15% at typical pressures. Of course, this could be significantly reduced, but as mentioned earlier it would add significantly to the cost of the unit and require an actuator and actuated damper. We have not (yet) seen any specifications calling for this degree of air tightness. The A&M report also stated that a parallel box would have to leak less than 7% to be more cost effective than a series box, from a total system standpoint.

So that’s where the industry is at this point with regard to air leakage. I expect that we will hear from the DOE in the future and that certain the rules will be tightened up, but sadly, the efforts are likely to generate little actual energy savings.

Authored by: Dan Int-Hout, Chief Engineer Krueger

Wednesday, May 7, 2014

Is it May already??

Sadly, ASHRAE still hasn’t published the letter to the Editor from our Engineering Manager on the Hospital OR article that made the cover of the Journal in February. (The one I wrote last year has received no comments.) The other articles I wrote have all been posted on our website under Learn > White Papers.

The big news is, of course, the purchase of Air Distribution Technologies (our parent company) by JCI (Johnson Controls). We have been assured that business will continue as always. The best part is that we are no longer being owned by a “holding company,” where our future was rather uncertain. We hope, of course, that the purchasing power and vast industry knowledge of our new owners will provide us with an array of new opportunities that will allow us to serve our customers better.

All that being said, I will continue towards my role as a member of ASHRAE’s board, effective after the summer meeting. I have been appointed to the Tech Council, where I will be able to see the ins and outs of technical activities. I was asked to prepare a short statement in response to the question “As ASHRAE moves ahead in developing a new strategic plan, what are the strengths of ASHRAE that we must not lose sight of?” I responded with the following, as printed in the April ASHRAE Insights.

“ASHRAE has a unique membership composed of manufacturers, academics, and design engineers. We need to make sure we take full advantage of the research capabilities and manufacturing expertise to provide the design community with the truly innovative, thoroughly tested, and affordable products and systems that meet our core goal: that of providing acceptable environments for the occupants of buildings that we heat, cool, and ventilate. In this way, we can ensure that healthy and comfortable folks continue to provide a record level of productivity in the workplace and at home. It would be an added bonus if we could, at the same time, minimize our impact on the environment by reducing energy use and minimizing unsustainable activities."

Authored by: Dan Int-Hout, Chief Engineer Krueger

Thursday, March 27, 2014

Krueger-HVAC Response to ASHRAE Journal Article on "Hospital OR Air Distribution"

In February, there was an ASHRAE Journal article on Hospital OR Air Distribution. After thoroughly reviewing it, we identified several technical flaws. It’s worth noting that the article I authored on the same subject was published in December 2013 (with quite different conclusions, I might add). Now with 11 articles having been accepted by the Journal as of recent, only a few are posted on our website, unfortunately. We will make them available as soon as we get approved copies from ASHRAE.

In response to the article, a letter to the editor was prepared by our Engineering Manager and will hopefully be published soon. Below is a quick summary of what was sent:

Summary of letter to the editor on “Improving Operating Room Contamination Control”

  1. The authors incorrectly state the four different ceiling air delivery scenarios meet ASHRAE Standard 170 guidelines for diffuser coverage over the patient table.
  2. The AC system doesn’t comply with the Space Ventilation requirements stated in section 7.1.a of ASHRAE Standard 170-2013.
  3. Based on the sizing of the AC system, one could also question the results for the MDA system.
  4. Splitting the MDA array completely across the table is one of the worst possible configurations for this type of system, especially since it happens right in the middle of the surgical table where it can induce contaminants rising from the patient.
  5. The author gives the room dimensions as 20 ft 5 in. W x 20 ft 7 in. L x 10 ft H for a room volume of 4,202 ft3 but uses a room volume of 4,800 ft3 to 4,822 ft3 for their ACH calculations.
  6. The author makes the statement – “The data also indicates that at equal size and airflow, a one or two ISO Class improvement was achieved between the MDA and SLD1 scenarios without additional energy consumption.” The data shows only a single ISO Class Improvement from ISO Class 8 for the MDA-30 to an ISO Class 7 for the SLD1-30 for systems complying with ASHRAE Standard 170-2013.

While this article is a good starting point for generating dialog on hospital OR environments, the study itself is flawed and looks to be more of a marketing/promotional piece for manufacturers of SLD systems.

The results are at odds with both the testing conducted by Krueger in the 1980’s with actual patients and with the Egyptian study I referenced in the ASHRAE Journal article (“Air Distribution in the OR”, December, 2013). This is to say, we are convinced that a properly designed air curtain system will provide the safest form of air distribution in a hospital setting.

BTW - Stay tuned to the Krueger website for exciting clean room developments soon to be released!

Thursday, February 20, 2014

ASHRAE Articles Authored by Dan Int-Hout (Update)

Now that we are settled after the January ASHRAE meeting, I have some interesting news to report. I have been named a Director At Large (DAL) for ASHRAE. I’ll be traveling to Atlanta at the end of January for training and then I’ll be able to report on what my duties will be. I will of course be attending all meetings of the Board of Directors, either in Atlanta at annual meetings or on-line. I am very excited about being able to use my experience as an ASHRAE member for 40 years to help the Society move forward. My tenure will be for three years, starting officially in June.

I now have 10 articles submitted or published in the ASHRAE Journal. I reported earlier on the first set, here are the summaries:

June 2013 - Slots are Adjustable
July 2013 - Comfort vs. Energy
August 2013 - VAV Research Validates Low Airflow Comfort
September 2013 - Balancing Factors

I reported on some of the details of these in a blog in September last year.

New are:

October 2013 - You Have to Prove It
Validation of computer models is necessary to prove that the input assumptions, and the math used is valid. All too often we are seeing estimates that just don’t pan out in practice.

December 2013 - Hospital Operating Room Air Distribution
I reported on the understandings of how air curtain systems in Hospital OR’s have been proven to be an effective way of reducing infection rates, the current article in the February issue notwithstanding.

January 2014 - Reheat Coil Issues and Answers
Hot water coils are being designed with cooler entering water than in the past and it is causing some selection issues. I discuss minimum flows, and issues with electric heaters as well.

February 2014 - High Bay Air Distribution
Providing temperature control and comfort in locations with high ceilings is always a challenge. I have provided some easy ways to estimate the effect of buoyancy on delivered air flows.

March 2014 - High Performance Air Distribution Systems
An ASHRAE multiple discipline task group (MTG) is looking at how to design air distribution systems for maximum efficiency and sustainability. I have offered the spin on the terminal end of things.

April 2014 (Just submitted) – Compliance to Standard 55 (Comfort)
Compliance with Standard 55 (Comfort) can appear to be complicated. I have offered a bit of history on the calculation methods and have shown an easy path to compliance.

Authored by: Dan Int-Hout, Chief Engineer Krueger

Wednesday, January 15, 2014

Cold Calls – “Our Electric Coils Aren’t Working”

With the record cold that has gripped the country, the last thing one wants to hear is that the heat isn't coming on! So, we looked into the issue and have found that in most cases, this complaint stems from the design engineer not understanding some basic facts regarding the proper use of a VAV reheat air terminal device.

The typical complaint we get on electric heat is that it doesn't come on because the airflow safety switch isn't “making”. There are several issues that need to be understood:

1. Energizing: With today’s DDC systems, there is always low voltage available and electric heat is energized through electronic relays. In the past, these were typically wire wound electromagnetic coil relay devices, triggered and powered by low voltage current. As of recent, we are employing solid state relays, which although more expensive, are silent. With older pneumatic systems, the circuitry was all high voltage, which sometimes caused issue with arcing across the contacts in the safety “sail switches”.

2. Safety: UL specifications (and logic) require that the electric heat not operate unless there is sufficient air flow across the coils. After the main relay that energizes the electric coils, there is an airflow proving device and an overheat “high limit” device and on Single Duct units, there is a manually re-settable high temperature thermal cutout.

3. Airflow Proving: The air proving device used in all Krueger boxes is a “sail switch”, which is actually a combination of a membrane and micro-switch. This is used as a differential pressure assembly with only the high side connected to a pickup in the air stream. The low side is typically open to the control enclosure. On some airflow switches, there is no connection tap on the low side. If the switch is installed in a relatively air tight enclosure, this can be a problem, so Krueger has elected to only use higher cost switches with a low side tap so we can reference the differential pressure outside the cabinet if desired.

4. Air Flow Pickup: The single point pickup probe is located at the point of highest airflow in the heater assembly. The single tube pickup is actually a “total pressure”, rather than a velocity pressure device, which would require two tubes.

5. The mechanics of this type of sail switch precludes a tight operating range specification, with the one Krueger uses having an 0.05” stated response, but with an accuracy of +/- 0.02”. We find that most operate (make) at about 0.03”. The published minimum airflows in the Krueger catalog develop less than 0.01” velocity pressure at the probe location, so Krueger requires that there be at least 0.03” downstream pressure in the airflow path to the room to get the necessary total pressure to engage the airflow switch.

So, knowing the “rules”, we can now look at the issues they raise. If a single duct VAV box is set to have heat come on at minimum VAV box airflow settings, it is very unlikely that downstream pressure will be as high as 0.03. If it were, and if the box is set at the typical 25% of cooling maximum air flow, the downstream pressure would 16 times higher at maximum flow! For a typical single duct VAV box electric heater, this is about 0.4”. Few systems are set to operate with downstream pressures this high.

This is compounded by the damper position in the VAV box. Even though we require a longer box when using electric heat, we still see a higher velocity pressure at the pickup location at partially closed damper positions than when the damper is fully open. With dynamic air handler system pressures being set so that at least one box has a fully open damper (as required in some codes), it is possible that a perimeter heating VAV box may have a fully open damper, but then it may not “make” even at the Krueger stated minimums. A balancing damper set to provide some back pressure may be required in some extreme cases.

In most cases, it shouldn't be a problem, that is, if the engineer is following good practice (and most codes) and limiting discharge temperatures to 90°F. This will usually require heating airflows to be higher than 25% of cooling maximums to meet the heating load requirements. DDC controllers make having a “dual minimum” as simple as just setting it up. (Older pneumatic systems require complex plumbing to achieve dual minimum control). The ASHRAE 90.1 energy standard, typically referenced in codes, now allows for reheat up to 50% of design cooling air flows if one starts at 20% and limits discharge temperatures and uses VAV heating. Of course, Krueger’s LineaHeat electric heat was designed with this as a standard feature should one add a temperature probe located downstream of the heater.

So in summary, a VAV box with electric heat will operate properly when the heating airflows are high enough to provide sufficient total pressure at the heater. This can usually be accomplished with sufficient airflow to meet the 90°F discharge limitation. If lower airflows are required, providing some static pressure resistance downstream may be needed.

Authored by: Dan Int-Hout, Chief Engineer Krueger

Wednesday, January 8, 2014

Top Ten HVAC Predictions for 2014

1. LEED V4, released last fall, includes a reference to either AHRI 885 or the ASHRAE Handbooks to prove compliance to acoustical requirements. The handbooks are missing a critical path table for the sound transmitted from a plenum noise source into a space. The incoming chair of TC 2.1 has indicated he will get the missing ceiling table included in the Handbooks. I predict he will fail in this effort for at least three years and that the 885 handbooks will be the only easy path to compliance. (One can hire an acoustician, of course, and TC 2.6 is populated with them).

2. Installed linear diffusers will still fail to have pattern controllers set prior to balancing. If adjusted after balancing, rebalancing is required. It is the design engineer’s responsibility to provide the adjustment information. The installing contractor should be designated as the one responsible for setting the pattern deflectors.

3. ASHRAE Thermal Comfort Standard (55-2013) has been modified to include Normative (mandatory) and Informative sections so that it can be referenced directly in codes. ADPI will be included by reference to the ASHRAE Handbooks, which will be updated to show the relationship between air distribution and thermal comfort.

4. There will still be no new published, peer reviewed, energy savings data for any of the “energy saving” systems (VRF, displacement, underfloor, or chilled beams), but engineers will continue to claim energy savings compared to overhead systems, to get LEED or Energy Star ratings.

5. The AHRI / ASHRAE study on whole system energy use of fan powered boxes will start to be integrated into the Energy Plus and possibly Trane Trace and Carrier HAP energy models under an AHRI research program.

6. The number 1 reason for not renewing the lease in high rise buildings will continue to be “occupant dissatisfaction with the building environment” (ie: comfort). It has been so for the past 20 years, so this is likely a ‘gimmee’. One can hope I miss this one.

7. The market for HVAC components will again be up about 5% with pent-up demand slowly coming back.

8. VAV overhead air distribution will continue to be (by far) the most used system in new buildings. As loads decrease, it will become more apparent that the ventilation load in the interior is the predominant building load. ASHRAE RP 1515 will open a lot of eyes. The report from the ASHRAE MTG on Advanced Air Distribution will be circulated showing paths to optimize system design.

9. While many VAV box schedules will continue to show design discharge temperatures in excess of 90°F, a number of Engineers will finally get it. (ps: Hot air rises!)

10. Sadly, I predict that the Cowboys will continue to wallow in the mud of disappointment.

Authored by: Dan Int-Hout, Chief Engineer Krueger

Thursday, January 2, 2014

Scoring on My Top Ten HVAC Predictions for 2013

1. LEED 2013 will be released in the fall, and it will include a reference to AHRI 885 to prove compliance to acoustical requirements. Done - 10 points

2. Balancers will continue to ignore the need to adjust linear diffusers before balancing. If adjusted after balancing, rebalancing is required. This is the design engineer’s responsibility, of course, so they need to require adjustment is they specify adjustable slots. I predict this will be ignored. (It’ll be an easy 10 points). Yup - 10 points

3. ASHRAE Thermal Comfort Standard (55-2010) will be modified to include Normative (mandatory) and Informative sections so that it can be referenced directly in codes. This is already partly accomplished. ADPI will be included in ASHRAE standard 55 as a means of predicting compliance. In progress - 7 points

4. The updated ASHRAE UFAD Design Guide will be published in 2013. Done - 10 points

5. We will see no published, peer reviewed, energy savings data for any of the “new” systems (displacement, underfloor, or chilled beams), but engineers will continue to claim energy savings compared to overhead systems, to get LEED or Energy Star ratings. Sadly, still no published validation - 10 points

6. BOMA will continue to state that the #1 reason for not renewing the lease in high rise buildings is “occupant dissatisfaction with the building environment” (ie: comfort). (It has been for the past 20 years, this is likely a ‘gimmee’.) Still the top reason - 10 points

7. The market for HVAC components will again be relatively flat with local ups and downs. Still flat - 10 points

8. VAV overhead air distribution will continue to be (by far) the most used system in new buildings. As loads decrease, it will become more apparent that the ventilation load in the interior is the predominant building load. ASHRAE RP 1515 will open a lot of eyes. Yup - 10 points.

9. The majority of VAV box schedules will continue to show design discharge temperatures in excess of 90F, in spite of the ASHRAE handbook stating this will guarantee non-compliance to Standard 55’s vertical temperature stratification limitation, and without compensating increases in ventilation, as required by Standard 62.1 (and code in most states). Again, this is sadly true - 10 points

10. Sadly, the Cowboys will continue to disappoint their fans. (Again) I’m tempted to give this bonus points, but I’m in a giving mood – 10 points.

97 Points total. Nostradamus has nothing!

(It’s easy to score high if you grade your own predictions….)

Authored by: Dan Int-Hout, Chief Engineer Krueger