2019 NACM: Lab Exhaust Recommendations from CASE Team

[joesinger12]

Baseline fan system and fan power

1. Fan system a. If minimum required ventilation flow rate is > 10 ACH, same as proposed design b. If minimum required ventilation flow rate is <= 10 ACH, variable volume exhaust fan c. If exhaust fan/s are constant volume i. Model one HVAC exhaust fan as constant volume ii. Model zone exhaust fan to account for bypass air needed to maintain target exit airflow rate d. If exhaust fan/s are variable volume i. Model one HVAC exhaust fan as variable volume
2. Fan power a. If exhaust fan airflow is <= 10,000 CFM, use requirements in section 140.4(c) for supply and exhaust fan power i. See Table 1404.4-A Fan Power Limitation and Table 140.4-B Fan Power Limitation Pressure Drop Adjustment b. If exhaust fan airflow is > 10,000 CFM, use requirements in section 140.4(c) for supply fan power (w/o exhaust system pressure credits) and use requirements in section 140.9(c)3b for exhaust fan power i. For supply fan power, see Table 1404.4-A Fan Power Limitation and Table 140.4-B Fan Power Limitation Pressure Drop Adjustment, excluding credits for
   1. Fume hoods
   2. Exhaust airflow control devices
   3. Biosafety cabinets
   4. Ducted exhaust
   5. Exhaust filters ii. For exhaust fan power
   6. If there is air filtration, scrubbers, or other air treatment devices in exhaust stream, use 0.85 W/CFM
      2. If there is no air filtration, scrubbers, or other air treatment devices in exhaust stream, use 0.65 W/CFM
      3. Sash closing controls (refer to inputs and schedule definitions below) a. If lab spaces are constant volume, fume hoods have constant volume schedule b. If lab spaces are variable volume and deemed NOT fume hood intensive (according to Table 140.9-B), use manual sash control fume hood schedule c. If lab spaces are variable volume and deemed fume hood intensive (according to Table 140.9-B), use automatic sash control fume hood schedule

Proposed fan system and fan power

1. Fan system a. Use design fan system i. If exhaust fan/s are constant volume

   1. Model one HVAC exhaust fan as constant volume
   2. Model zone exhaust fan to account for bypass air needed to maintain target exit airflow rate ii. If exhaust fan/s are variable volume
   3. Model one HVAC exhaust fan as variable volume b. Fan staging for constant volume fans i. If fans are not staged
      1. Split airflow equally amongst all exhaust fans (model as 1 HVAC exhaust fan) ii. If fans are staged
      2. Exhaust all air from one exhaust fan until exhaust airflow rate exceeds target exit airflow rate, then turn next fan on; continue process until all exhaust fans are in use
   2. Fan power a. If no wind-responsive control or contaminant-responsive control i. Use design fan power b. If wind-responsive control or contaminant-responsive control i. If there is air filtration, scrubbers, or other air treatment devices in exhaust stream, use 0.85 W/CFM ii. If there is no air filtration, scrubbers, or other air treatment devices in exhaust stream, use 0.65 W/CFM
2. Sash closing controls (refer to inputs and schedule definitions below) a. If lab spaces are constant volume, fume hoods have constant volume schedule b. If lab spaces are variable volume and deemed NOT fume hood intensive (according to Table 140.9-B), use manual sash control fume hood schedule c. If lab spaces are variable volume and deemed fume hood intensive (according to Table 140.9-B), use automatic sash control fume hood schedule

For each constant volume lab space (room), the following inputs are needed:

1. Conditioned volume of the space (V)
2. Minimum ventilation ACH (ACH)

Error check, warn user if ACH < 4. Design exhaust CFM = ACH x V / 60 Hood schedule remains unchanged from pre-existing constant flow fraction schedule of 0.90.

For each variable volume lab space (room), the following inputs are needed:

1. Conditioned volume of the space (V)
2. Rated CFM of vertical sash fume hoods with automatic sash control (CFMva)
3. Rated CFM of vertical sash fume hoods with manual sash control (CFMvm)
4. Rated CFM of all other fume hoods (CFMo)
5. Minimum ventilation ACH occupied hours (ACHo)
6. Minimum ventilation ACH unoccupied hours (ACHu)

Error check, warn user if either ACH < 4.

Proposed Design Case Exhaust CFM: Occupied Hours Exhaust CFM = CFMo = Max{[ACHo x V / 60] , [(CFMvm + CFMo) x Pm,h + CFMva x Pa,h]} Unoccupied Hours Exhaust CFM = CFMu = Max{[ACHu x V / 60] , [(CFMvm + CFMo) x Pm,h + CFMva x Pa,h]}

Standard Design Case Exhaust CFM if deemed a fume hood intensive space: Occupied Hours Exhaust CFM = CFMo = Max{[ACHo x V / 60] , [CFMo x Pm,h + (CFMvm + CFMva) x Pa,h]} Unoccupied Hours Exhaust CFM = CFMu = Max{[ACHu x V / 60] , [CFMo x Pm,h + (CFMvm + CFMva) x Pa,h]}

Standard Design Case Exhaust CFM if deemed not a fume hood intensive space: Occupied Hours Exhaust CFM = CFMo = Max{[ACHo x V / 60] , [(CFMo + CFMvm + CFMva) x Pm,h]} Unoccupied Hours Exhaust CFM = CFMu = Max{[ACHu x V / 60] , [(CFMo + CFMvm + CFMva) x Pm,h]}

Reported by: joesinger12

Original Ticket: cbecc-com/tickets/2955

[joesinger12]

• assigned_to: Nikhil Kapur --> David Reddy

Original comment by: joesinger12

[joesinger12]

Separate Ventilation and Exhaust Tabs into two individual tabs for 2019

Original comment by: joesinger12

[joesinger12]

Notes from 2/27 call:

• Revise VentSpcFunc list to allow specification of non-educationl lab, which should not have a minimum required exhaust ventilation. DR to coordinate with with RHe on VentSpcFunc naming for labs.
• DR to review E+ 9.0 documentation to see if we can model exhaust fans following a fan curve
• CEC comfirmed that it is not necessary for the user entered minimum exhaust flow to be consistent with the simulated minimum exhaust flow, as determined by the prescribed variable exhaust flow fraction curves.
• Team decided that we should just adopt the CASE guidance and curves for how labs should be modeled. This includes:
  • Inputs for CFMva, CFMvm, CFMo
  • Clarify that hood length input is vertical + horizontal
  • Move exhaust inputs to a new Tab of Space dialog
• DR to follow-up with JM on a few clarifications, including the following:
  • CFMo is defined as "Rated exhaust CFM of all other fume hoods". Is CFMo also intended to include all other exhaust devices, such as snorkels, cabinets, etc? If not, should exhaust for all these other applications assumed to be constant?
  • Is it safe to assume the simulation should reflect that the HVAC system supply OA always balances, or is slightly positive, with the hourly exhaust flows? I see you've defined hourly exhaust flow to track the max the calculated exhaust or the minimum occupied/unoccupied ventilation rates. The schedules you've provided are for the exhaust flow, but based on this, I'd expect that these schedules would alos describe the VAV terminal min flows on the supply side as well.

Original comment by: joesinger12

[joesinger12]

Original comment by: joesinger12

[joesinger12]

Additional clarification:

For Variable Volume Exhaust, there are two options: VariableFlowConstantSpeedFan VariableFlowVariableSpeedFan

VFCS Fan assumes the zone exhaust flow varies, but the power (and therefore exhaust fan flow schedule) is the same as constant speed fan since power is still needed to move bypass air. However, in simulation, this schedule also drives the supply flow rate. Therefore, I think we need to use the variable flow schedule for the system supply min flow sched.

Original comment by: joesinger12

[joesinger12]

We checked how the Fan:ZoneExhaust object power varies with flow. As we had guessed, it is linear. Therefore, variable flow exhaust, at least as we have modeled it, will not follow the fan power law that one might expect.

Original comment by: joesinger12

[joesinger12]

New Schedule for CFMo to be added in fall. JA to follow up with CASE team on the actual schedule.

Original comment by: joesinger12

[joesinger12]

Q1: CFMo is defined as "Rated exhaust CFM of all other fume hoods". Is CFMo also intended to include all other exhaust devices, such as snorkels, cabinets, etc? If not, should exhaust for all these other applications be assumed to be constant?

Reply: Yes. CFMo is intended to include all other exhaust devices, such as snorkels, cabinets etc. Exhaust for all these other applications in the standard design should be the same as in the proposed design. I recommend using the manual control profile for these "other" exhaust devices. In general the profile is relatively constant.

Optional Capability: However you might consider including a checkbox and data entry that allows the proposed design to have lower flowrates at night and weekends (exhaust system pressure dropped to reflect different minimum ACH), the same would also be applied to the standards case. It would have a second order effect on the automatic sash controls. The primary reason for doing this is so the ACM provide the capability to match a design option that is commonly applied. Not critical for this measure but provides user confidence that the ACM represents the design.

Original comment by: joesinger12

[joesinger12]

Q2: Is it safe to assume the simulation should reflect that the HVAC system supply OA always balances, or is slightly positive, with the hourly exhaust flows? I see you've defined hourly exhaust flow to track the max calculated exhaust or the minimum occupied/unoccupied ventilation rates. The formulas you've provided clarify the hourly exhaust flow, but based on this, I'd expect that these schedules would also dictate the VAV terminal min flows on the supply side as well. Reply: Typical design practice is that the lab is depressurized from the surrounding area so there is not leakage into hallways or other spaces. Typical practice is to have 10% less outside air being brought into the space than the exhaust flowrate so the space is depressurized and drawing in air from leakage from other spaces etc. Thus there is typically around 10% "transfer air" regardless of whether there being an actual transfer ducts but rather leakage under doors and infiltration from surrounding spaces and from outside. Thus HVAC system supply air flow should always be less than or equal to exhaust flow. There should be an error or warning if the simulation ever has more outside airflow than exhaust airflow. We will look into typical construction practices in regards to a specified transfer air ducts or whether this is mostly accomplished through lab depressurization and air leakage between zones.

There was a fairly significant effort in the prescriptive standards to clarify the requirements for transfer air requirements. Primary areas where the transfer air requirements have a significant impact are those space where exhaust air flows are large this would include: • Kitchens • Laboratories • Other areas listed in Table 120.1-B – Minimum Exhaust Rates Thus we recommend that the rule sets that the NR ACM team are developing for transfer air that laboratory transfer air rules be scrutinized as this is a key area which most times will use as much transfer air as is available from nearby zones.

Original comment by: joesinger12

[joesinger12]

As mentioned earlier these are our key recommendations for ACM improvements to laboratory HVAC rulesets:

1. System mapping of smaller labs uses VAV systems with 20% min flow and not SZVAV with 50% min flow. Single zone systems with only 50% turndown are rarely used for labs. This should be matched to building size with large buildings using chilled water systems (System 6 VAVS) and smaller buildings using DX VAV (System 5 PVAV).
2. Lab hood flow hourly schedules from Appendix 5.4B _Schedules-T-24N.xlsx should match the flow schedules that were used to the develop the High Efficiency Fume Hoods in Laboratory Spaces CASE report. NORESCO modified these profiles based on trying to match energy savings but they did not use minimum ACH rates - this incorrectly skewed the results towards using lower profile values.
3. The ACM ruleset should reflect that even if the proposed design is greater than 10 ACH, if the exhaust system is VAV then automatic sash closure controls are modeled in the standard design on fume hoods with vertical sashes in spaces that qualify as Fume Hood Intensive Laboratories.
4. In the earlier draft of the ACM, the standard design has minimum exhaust flow or ventilation rates that are the greater of the proposed design and a fixed ACM. The programmer of compliance software cannot know what the health and safety requirements are for all labs. These minimum flowrates are something determined by the designer in conjunction with regulatory authorities. These minimum flowrates are health and safety requirements, we recommend that the ACM not model the greater of the proposed design and a fixed ACH for the standard design. Instead the standard design min ACM should be equal to the proposed design min ACM.
5. ACM should clarify that the length of all fume hoods (and not just those with vertical sashes) are included in the calculation of Fume Hood Intensive Laboratories.

Original comment by: joesinger12

[joesinger12]

Re: Q2 (transfer air rules), this feature won't implemented for RC release.

Original comment by: joesinger12

[joesinger12]

Re: VentSpcFunc updates:

From DR 4/2 to NORESCO/CEC:

I'm updating the VentSpcFunc list based on the clarification that according to the code, education labs have a minimum exhaust rate, but 'Other' labs don't (i.e. a lab in a start-up biotech).

Per our recent discussions, the assumption is standard = proposed design ventilation and exhaust rates. The only rule that we will enforce is that educational labs have a minimum of 1 cfm/SF of exhaust, per Table 120.1-B. Please confirm.

Also, reviewing Table 120.1-A, it seems odd that there is an entry for both "Science laboratories " and "University/college laboratories", despite they have the same ventilation required value. In CBECC-Com, we have SpcFunc "Scientific Laboratory Area", and VentSpcFunction options of "Education - Science laboratories" and "Education - University/college laboratories", both of which are assumed to require the exhaust specified as "Educational science laboratories" included in Table 120.1-B. It redundant to have both. For CBECC-Com, do we want to collapse this into one VentSpcFunc selection: "Education - Science Laboratories"? It's OK if we want to leave them separate, but if we are making other changes to labs, I thought I'd ask.

Either way, I need to add an additional VentSpcFunc for non-educational scientific labs. I was thinking 'Misc - Science laboratories'. Please let me know if you have any other preferences.

Response from RH 4/3: I agree that there is no minimum exhaust rate in the standard, or in 62.1, for labs other than Educational Science Laboratories. So you will include a minimum exhaust rate as well as a minimum ventilation rate for both “Science laboratories” and “University/college laboratories”? I think that is the right approach.

I agree that it is odd that 62.1 includes two space types which seem so similar and have identical requirements. I looked back at old versions of the Standard to see if they had different requirements in some older version, but what I found was that 62.1-2004 included only “Science laboratories” and that “University/college laboratories” were added to the 2007 version for some reason. (I’ll note that the 2007 version was prepared during I time when I was not on the committee but on Standards Committee instead, so don’t blame me.) I agree the two space functions are redundant, but I think it may result in confusion if the space types in CBECC don’t match up with those in the standard, so I would recommend leaving both in CBECC-Com.

I think adding a “Misc – Science laboratories” VentSpcFunc will be problematic, because there is no such vent function in the standard. Designers must pick a ventilation Occupancy Category from Table 120.1-A or 120.1-B, so we can only offer selections from those tables. In this case, I think that under the SpcFunc of “Scientific Laboratory Area” we should allow selection of the VentSpcFunc “Misc – All others.” This will trigger a minimal ventilation requirement, but allow them to specify a larger ventilation rate in accordance with the design. This combination of SpcFunc and VentSpcFunc should then be modeled in the baseline with ventilation that matches the proposed.

Response from DR 4/3: OK, this works for me Roger, thanks for your input. And in answer to your question, Yes, since we will maintain them both, the software will enforce a minimum exhaust rate (1.0 cfm/SF) as well as a minimum ventilation rate (o.15 CFM/SF) for both “Science laboratories” and “University/college laboratories”.

Response from RJ 4/3: Works for me too.

Original comment by: joesinger12

[joesinger12]

• status: New --> Fixed

Original comment by: joesinger12

[joesinger12]

Major updates for thsi ticket committed @ r5854 & r5855 of 2019-1-0_RC-DRDev branch

Still to confirm:

• KITCH (system 13) requirements. Updates reflect NACM language suggested to CEC:

Dedicated single-zone makeup air unit (MAU) with dedicated exhaust fan. If the building is VAVS per Table 3, the cooling source is chilled water and the heating source is hot water. Otherwise, cooling source is DX and heating source is a gas furnace.

• System/exhaust air flow tracking for labs
• Fumehood intensive lab criteria based on density of proposed system, not zone or building

Original comment by: joesinger12

[joesinger12]

• status: Fixed --> Started
• Version: CBECC-Com 2019 RV --> CBECC 2022

Original comment by: joesinger12

[joesinger12]

Based on user questions about lab rules, it was found that when building lab exhaust met criteria for 140.9(c)3B (lab exhaust flow > 10000 CFM), the fan power adjustment to 0.85 W/cfm was occurring if FullyDuctedExh, ExhFilters, BiosftyCabExh PD credits were checked. CEC clarified that the power should only be triggered if ExhFilters credit is non-zero.

Original comment by: joesinger12

[joesinger12]

• Version: CBECC 2022 --> CBECC-Com 2019.1.3 SP1
• Milestone: Com2019.1.0 --> Com2019.2.0

Original comment by: joesinger12

[joesinger12]

Fix for baseline lab exhaust fan power discrepency described above:

Revision: 6743 Author: davidreddy Date: Thursday, September 23, 2021 10:30:31 PM Message: Ticket 2955: Fix baseline lab exhaust fan power when 140.9(c)3 applies. Previously, when building lab exhaust met criteria for 140.9(c)3 (lab exhaust flow > 10000 CFM), the fan power adjustment to 0.85 W/cfm was occurring if FullyDuctedExh, ExhFilters, BiosftyCabExh PD credits were checked. CEC clarified that the power should only be triggered if ExhFilters credit is non-zero. This commit fixes that. Screens updated to not show FullyDuctedExh & BiosftyCabExh PD credits when Bldg:LabExhFlow > 10000 Also:

• Update exhaust fan rules to address issue of small discrepancy between baseline intended target and actual simulated fan power when the baseline exhaust fan power is defined in terms of W/cfm.
• Fix minor rule eval and CHECK rule bugs in recent A2AHR updates merged in by JP

• Merge recent 2019 screen updates into 2022 screens

  Modified : /branches/CBECC-Com_EnergyPlus94/RulesetDev/Rulesets/T24N/Rules/HVACSecondary-Fan-Exhaust-T24N.rule Modified : /branches/CBECC-Com_EnergyPlus94/RulesetDev/Rulesets/T24N/Rules/HVACSecondary-Fan-General.rule Modified : /branches/CBECC-Com_EnergyPlus94/RulesetDev/Rulesets/T24N/Rules/HVACSecondary-Fan-Pressure Credits-T24N.rule Modified : /branches/CBECC-Com_EnergyPlus94/RulesetDev/Rulesets/T24N/Rules/HVACSecondary-HeatRecovery.rule Modified : /branches/CBECC-Com_EnergyPlus94/RulesetDev/Rulesets/T24N/T24N Screens.txt Modified : /branches/CBECC-Com_EnergyPlus94/RulesetDev/Rulesets/T24N/T24N_2022 Screens.txt

Original comment by: joesinger12

[joesinger12]

• Milestone: Com2019.2.0 --> ComDevIssue

Original comment by: joesinger12

[joesinger12]

• Milestone: ComDevIssue --> CBECC2022DevIssues

Original comment by: joesinger12