IEQp1 Review Comments

The mechanical schedule shows each air-handling unit's performance values itemized, within a table. The schedule will typically include the design supply airflow, outdoor airflow, cooling coil parameters, and electrical data.

If the unit is constant volume, include that in your response. Also describe that the unit is a cooling only system. For most cooling only applications, ou can use an Ez of 1.0. It is when you have a heating condition that an Ez of 0.8 is sometimes necessary.

We've noted that a lot of recent reviews from GBCI result in the same set of comments, regardless of the actual design. GBCI wants the design team to validate that common design oversights have been avoided.

Fabiano, with regards to your question #4 - Zones are not the same as spaces. If you have a unit that serves 3 different spaces (an office, conference room and hallway) it is only a Multi-Zone system if each space has a separate zone control (eg thermostat connected to a vav box or reheat coil). Often constant volume units only have one thermal control zone.

The Ez 0.8 demand is recent. You do not learn about this until the review.

Heating generally occurs during startup periods and when occupancy is low. When heating occurs when occupancy it is higher it usually a result of outdoor air conditions being outside the ASHRAE 90.1 design conditions for the system.

Simply, HVAC systems are not designed to meet 100% of weather conditions.

Unfortunately, the USGBC's LEED Department, which writes and keeps changing the the review comment you got, insists that ASHRAE 62.1 consider 100% of the load hours while ASHRAE 90.1 does not require that. You will never convince them they have not considered how HVAC systems actually ventilate a space.

Okay, so now what? The only thing you can try, if you don't want to blindly claim 100% of heating hours using EZ 0.8, is determine an occupancy percentage when heating might occur in your building during normal operational hours. You can try assuming normal ASHRAE thermal design conditions (this would drop out the winter low extreme). Use the occupancy percentage in the EZ 0.8 calculations.

To be complete, you also have to analyze EZ 1.0 at 100% occupancy conditions. You then have to base the LEED requirements on the worst case, heating or cooling. Conference rooms, for example, should always bee dominated by cooling loads. heating should only occur when occupancy is low in such a room.

Doing it the way I described results in some HVAC systems being critical with EZ 1.0, and some with EZ 0.8. The end result depends on the occupancy type of the space.

What I described is the proper way to analyze ventilation rates; consider both heating and cooling, ignore start ups, ignore weather extremes, consider occupancy percentage. Someday, the USGBC will figured this out.

Fabiano,

If you find out the calculations result in the project not complying with ASHRAE 62.1, this is how you can fix it.

The ASHRAE 62.1 calculation tool, originally developed by Dennis Stanke, is a design tool. It is not a compliance tool, which is what the USGBC has turned it into.

ASHRAE has never provided documentation describing how to use the tool to design ventilation rates.

If you find a system that fails, it fails because the "critical zone" is under-ventilated. Within the system all other zones are not "critical zones," and are therefore over-ventilated with respect to the "critical zone."

If you system is adequately sized, which is almost always the case--engineers tend to be conservative with sizing--, you can "borrow" ventilation air from an over-ventilated space and use it to improve performance in the "critical" zone. The "critical zone" will likely move to a different space, depending on how much air you chose to borrow.

If your project is already built, then you need to conduct a new TAB for the affected zones you changed the ventilation rates.

Regardless of comments made, by others in this forum topic, submitting a TAB for the ventilation prerequisite is what should be provided to prove the rates were indeed changed after the design completion.

You should be able to submit only the new TAB for the revised zones only as you backup documentation. I did have a project, now certified Gold, where the reviewers challenged the entire calculation method done by the design engineer. I had to redo the entire calculations, and using the final TAB plus a supplemental TAB for zones the engineer did not properly ventilate. The owner had to redo TAB for about 10% of the zones. The overall system ventilation rate, and OA amount, remained as originally designed. Only the ventilation distribution changed.

This is one of the LEED review demand requirements the USGBC fails to document anywhere. There are many of these, and they change on a constant basis.

The LEED Reference Guide fails to describe how to analyze projects under heating and cooling modes of operation; it only shows cooling mode at the system level, rather than at the occupied zone level.

I got a review comment, after challenging the "heating" is the dominate ventilation mode, claim by the LEED reviewers, stating that the ASHRAE 62.1 User Manual said so. They did not base the claim on the actual standard, instead they used the User Manual. There is nothing in the User Manual stating heating is always the critical mode. In fact, the manual states cooling is usually the critical mode, and sometimes, heating.

From the ASHRAE 62.1-2007 User Manual.

Example 6-G:
Q: A ventilation system is designed so that the 150 fpm supply jet reaches to 4 ft above the floor with less than 15°F supply to room air temperature difference during steady-state heating conditions, but during morning warm-up, the temperature difference rises to 25°F. Does this large temperature system mean the zone ventilation effectiveness, Ez, must be assumed to be 0.8?
A: No, provided the warm-up cycle occurs before the space is occupied, as is generally the case. (Typically the outdoor air intakes are closed during warm-up so Ez is not relevant.)

Example 6-M—Finding Critical Zones in Multiple Zone Recirculating Systems. Read the A(nswer).

Example 6-N—Applying the Appendix A Method to VAV Systems:
Design cooling condition with the critical zone at its minimum expected airflow rate: This condition is often critical because the percentage of outdoor air needed for the system is at its smallest while the critical zone Zp or Zd value is at its highest...
Design heating condition: This condition can be critical since zones are typically at their minimum airflow rates and zone air distribution effectiveness can be low (e.g. 80%). Using the 62MZCalc spreadsheet, set the system and zone variables to the conditions they operate at when the system is on a design heating day at peak occupancy at steady-state.

In the above "Design Heating Condition" the peak occupancy means the number of occupants when heating is occurring on the "design" heating day. That is not necessarily 100% occupancy for transient use spaces, such as conference rooms, but can be the case at the start of a day before the building is warmed up by internal loads and people.

The reason you are now seeming this tied across to the Energy Analysis, is that someone who is consulting to the USGBC's LEED Department, decided that the way to prove heating is used in a building is to look at the energy results. If any heating load is shown therefore heating must be the dominate ventilation mode. This is not correct. Cooling can be the dominate mode, depending on occupancy percentages and space use.

The actual ASHRAE 62.1 User Manual contradicts the USGBC's standardized review response.

Fabiano,
What I understand from your post regarding the LEED reviewer's comments is that you included a heating system in your energy model just to comply with the requirement of ASHRAE 90.1. The LEED reviewer noticed that you included heating in your energy model and incorrectly concluded that your project actually intended to provide heating for those zones. Then the reviewer stated that should have calculated your ventilation for those zones using heating as your critical condition.

If that's what the case is, then simply write a response to the LEED reviewer explaining that these zones are cooling only and keep the Ev. at 1.0.

Hmmm, I have tried as Dylan suggested and had that rejected. The reviewers insisted that since there were heating loads in the energy analysis that Ez 08.8 must be used.

Dylan, have you found otherwise? Interestingly, the project the Ez 0.8 demand was made on was one where Glumac was the design engineer.

Hernando,
No one can guarantee a method will work every time with LEED. The reviewers are variable and the interpretations change often. That said, after many VRP calculations I've never had an issue with this before.

The reviewers comments stated:
"Although VRP calculations for cooling-only mode are acceptable, as noted in Preliminary comment #1, the mechanical schedules were not provided. The schedules are needed in order to confirm that the VRP calculations are appropriate for the ventilation system design,..."

It sounds to me like the Reviewer didn't have much information provided to them. As such they used the energy model data to determine what the systems were and how they operated. This is a pre-req, so you don't want to mess around with no getting this one. Perhaps you could send the reviewer the question before resubmitting.

Yes, Glumac and I got a reviewer who did not understand the credit.

The LEED review comment made was:
"ASHRAE 62.1-2004 Users Manual, page 6-16, states "The supply air temperature used in determining Ez for the zone calculation must be that which can be expected to occur when the space is occupied and which results in the lowest value of Ez." Therefore, the value for Ez is not the predominant condition but is the worst case scenario, and for this project should be 0.8.

Glumac provided an excellent ventilation submittal. VAV was assumed operating at minimum ventilation modes. The OA provided was more than double the amount required. Glumac used Ez 1.0 because they insisted they could get that approved.

Somehow, the reviewer managed to do a side calculation, using an unexplained method that showed the prerequisite was achieved by not the 30% greater credit.

It is not possible to change Ez from 1.0 to 0.8, have a system supply more than 100% additonal OA and show the prerequisite earned but not the 30% more credit. In fact, even if the Ez was 0.5, a system providing double the required OA will always meet the 30% requirement.

To this day, I have no idea how the reviewer managed to botch their math. Entering the system data into the ASHRAE tool would have confirmed the system meet the requirements, no matter how hard they tried to prove it did not comply. The only way for the reviewer to prove that would be to claim the provided OA was less than documented.