Energy Code Ace - 6. Exhaust Air Heat Recovery

SECTION 140.9 – PRESCRIPTIVE REQUIREMENTS FOR COVERED PROCESSES

(a) Prescriptive Requirements for Computer Rooms. Computer rooms with a power density greater than 20 W/ft² shall comply with this section.

1. Economizers. Each individual cooling system primarily serving computer rooms shall include either:

A. An integrated air economizer capable of providing partial cooling even when additional mechanical cooling is required and capable of providing 100 percent of the expected system cooling load at 65°F to 80.6°F supply air temperature at outside air temperatures of 65°F dry-bulb and below or 50°F wet-bulb and below, and be equipped with a fault detection and diagnostic system as specified by Section 120.2(i); or

B. An integrated water economizer capable of providing partial cooling even when additional mechanical cooling is required and capable of providing 100 percent of the expected system cooling load at 65°F to 80.6°F supply air temperature at outside air temperatures of 50°F dry-bulb and below or 45°F wet-bulb and below.

Exception 1 to Section 140.9(a)1: Individual computer rooms with an ITE design load under 5 tons (18 kW) in a building that does not have any economizers.

Exception 2 to Section 140.9(a)1: A computer room with an ITE design load less than 20 tons (70 kW) may be served by a second fan system without an economizer if it is also served by a fan system with an economizer that also serves other spaces within the building, provided that all of the following are

i. The economizer system is sized to meet the design cooling load of the computer room when the other spaces within the building are at 50 percent of their design load at outside air temperatures of 65°F dry-bulb and below or 50°F wet-bulb and below; and

ii. An economizer system that can stop service to other spaces in the building when those spaces are unoccupied and serve only the computer rooms.

2. Power Consumption of Fans. The total fan power at design conditions of each fan system shall not exceed 27 W/kBtuh of net sensible cooling capacity.

3. Air Containment. Computer rooms with air-cooled computers in racks and with a ITE design load exceeding 10 kW (2.8 tons) per room shall include air barriers such that there is no significant air path for computer discharge air to recirculate back to computer inlets without passing through a cooling system.

Exception 1 to Section 140.9(a)3: Expansions of existing computer rooms.

Exception 2 to Section 140.9(a)3: Computer racks with a design load less than 1 kW (0.28 tons) per rack.

Exception 3 to Section 140.9(a)3: Equivalent energy performance based on computational fluid dynamics or other analysis.

4. Alternating Current-Output Uninterruptible Power Supplies (UPS). Alternating current-output UPS systems serving a computer room shall meet or exceed minimum average efficiencies in Table 140.9-B. Minimum average efficiency for alternating current-output UPS shall meet or exceed calculation and testing requirements identified in ENERGY STAR Program Requirements for Uninterruptible Power Supplies (UPSs) – Eligibility Criteria Version 2.0.

Where:

P is the rated output power in watts (W).

E_MOD is an allowance of 0.004 for modular UPSs applicable in commercial 1,500-10,000 W range.

ln is the natural logarithm.

The requirement shall be rounded to the third decimal place for certification and reporting.

Exception to Section 140.9(a)4: Alternating current-output UPS that utilizes standardized NEMA 1-15P or NEMA 5-15P input plug, as specified in ANSI/NEMA WD-6-2016.

Table 140.9-B Alternating Current-Output Uninterruptible Power Supply Minimum Average Efficiency

AC Output	Voltage and Frequency Dependent	Voltage Independent	Voltage and Frequency Independent
P≤350 W	5.71 x 10^-5 x P + 0.962	5.71 x 10^-5 x P + 0.964	0.011 x ln(P) + 0.824
350 W<P≤1,500 W	0.982	0.984	0.011 x ln(P) + 0.824
1,500 W<P≤10,000 W	0.981 – E_MOD	0.980 – E_MOD	0.0145 x ln(P) +0.800 – E_MOD
P>10,000 W	0.970	0.940	0.0058 x ln(P) + 0.886

(b) Prescriptive requirements for commercial kitchens.

1. Kitchen exhaust systems.

A. Replacement air introduced directly into the hood cavity of kitchen exhaust hoods shall not exceed 10 percent of the hood exhaust airflow rate.

B. For kitchen/dining facilities having total Type I and Type II kitchen hood exhaust airflow rates greater than 5,000 cfm, each Type I hood shall have an exhaust rate that complies with Table 140.9-C. If a single hood or hood section is installed over appliances with different duty ratings, then the maximum allowable flow rate for the hood or hood section shall not exceed the Table 140.9-C values for the highest appliance duty rating under the hood or hood section. Refer to ASHRAE Standard 154-2011 for definitions of hood type, appliance duty and next exhaust flow rate.

Exception 1 to Section 140.9(b)1B: 75 percent of the total Type I and Type II exhaust replacement air is transfer air that would otherwise be exhausted.

Exception 2 to Section 140.9(b)1B: Existing hoods not being replaced as part of an addition or alteration.

TABLE 140.9-C - MAXIMUM NET EXHAUST FLOW RATE, CFM PER LINEAR FOOT OF HOOD LENGTH

Type of Hood	Light Duty Equipment	Medium Duty Equipment	Heavy Duty Equipment	Extra Heavy Duty Equipment
Wall-mounted Canopy	140	210	280	385
Single Island	280	350	420	490
Double Island	175	210	280	385
Eyebrow	175	175	Not Allowed	Not Allowed
Back shelf / Passover	210	210	280	Not Allowed

2. Kitchen ventilation.

A. Mechanically cooled or heated makeup air delivered to any space with a kitchen hood shall not exceed the greater of:

i. The supply flow required to meet the space heating and cooling load; or

ii. The hood exhaust flow minus the available transfer air from adjacent spaces. Available transfer air is that portion of outdoor ventilation air serving adjacent spaces not required to satisfy other exhaust needs, such as restrooms, not required to maintain pressurization of adjacent spaces, and that would otherwise be relieved from the building.

B. A kitchen/dining facility having a total Type I and Type II kitchen hood exhaust airflow rate greater than 5,000 cfm shall have one of the following:

i. At least 50 percent of all replacement air is transfer air that would otherwise be exhausted; or

ii. Demand ventilation system(s) on at least 75 percent of the exhaust air. Such systems shall:

a. Include controls necessary to modulate airflow in response to appliance operation and to maintain full capture and containment of smoke, effluent and combustion products during cooking and idle; and

b. Include failsafe controls that result in full flow upon cooking sensor failure; and

c. Include an adjustable timed override to allow occupants the ability to temporarily override the system to full flow; and

d. Be capable of reducing exhaust and replacement air system airflow rates to the larger of:

(i) 50 percent of the total design exhaust and replacement air system airflow rates; or
(ii) The ventilation rate required as specified by Section 120.1(c)3.

iii. Listed energy recovery devices with a sensible heat recovery effectiveness of not less than 40 percent on at least 50 percent of the total exhaust airflow; or

iv. A minimum of 75 percent of makeup air volume that is:

a. Unheated or heated to no more than 60°F; and

b. Uncooled or cooled without the use of mechanical cooling.

3. Kitchen exhaust system acceptance. Before an occupancy permit is granted for a commercial kitchen subject to Section 140.9(b), the following equipment and systems shall be certified as meeting the acceptance requirements for code compliance, as specified by the Reference Nonresidential Appendix NA7. A certificate of acceptance shall be submitted to the enforcement agency that certifies that the equipment and systems meet the acceptance requirements specified in NA7.11.

Exception to Section 140.9(b): healthcare facilities.

(c) Prescriptive requirements for laboratory and factory exhaust systems.

1. Airflow reduction requirements. Building laboratory exhaust systems shall be able to reduce zone exhaust and makeup airflow rates to the occupied and unoccupied minimum exhaust airflow rates based on demand and sensed occupancy as follows:

A. Occupied minimum exhaust airflow. When occupant sensing controls sense occupants in the space, the minimum exhaust and makeup airflow rates shall be the greater of:

User-defined airflow not to exceed 1.0 cfm/ft2 (equivalent to 6 air changes per hour for a 10-foot high ceiling), or
The regulated minimum occupied circulation rate documented to comply with code, accreditation, or facility environmental health and safety department requirements, or
The minimum needed to maintain occupied pressurization.

B. Unoccupied minimum exhaust airflow. Within 20 minutes of no occupancy being detected by any occupant sensors covering the space, the minimum exhaust and makeup airflow rates shall be the greater of:

User-defined airflow not to exceed 0.67 cfm/ft2 (equivalent to 4 air changes per hours for a 10-foot high ceiling), or
The regulated minimum unoccupied circulation rate documented to comply with code, accreditation, or facility environmental health and safety department requirements, or
The minimum needed to maintain unoccupied pressurization.

C. Applicable equipment and systems shall be certified as meeting the acceptance requirements for code compliance, as specified by the reference Nonresidential Appendix NA7.16. A certificate of acceptance shall be submitted to the enforcement agency that certifies that the equipment and systems meet the acceptance requirements specified in NA7.16.

Exception to Section 140.9(c)1: New zones on an existing constant volume exhaust system.

2. Exhaust System Transfer Air. Conditioned supply air delivered to any space with mechanical exhaust shall comply with the requirements of Section 140.4(o).

3. Fan System Power Consumption. All newly installed fan exhaust systems serving a laboratory or factory with a design exhaust fan system airflow rate greater than 10,000 cfm shall meet Subsection A and either B, C, or D. Exhaust air in laboratories or factories includes all indoor air and gases removed by the exhaust system including exhaust air from fume hoods, hazardous exhaust flows, or other manifolded exhaust streams. Exhaust fan system airflow rate is the total of the airflow rates entering the exhaust fans which includes exhaust air and bypass air but does not include entrained or induced airflow downstream of the exhaust fans:

A. Systems serving laboratory spaces shall meet all discharge requirements in ANSI Z9.5-2022 Section 6.4.

B. The exhaust fan system electrical input power (Fan kWdesign,system) determined per Section 140.4(c)1B at the fan system design airflow does not exceed Fan kWbudget as calculated per Section 140.4(c)1A.

C. The exhaust fan system power shall not exceed 0.85 watts per cfm of exhaust fan system airflow for systems with air filtration, scrubbers, or other air treatment devices. For all other exhaust fan systems the system power shall not exceed 0.65 watts per cfm of exhaust fan system airflow. Exhaust fan system power equals the sum of the power of all fans in the exhaust system that are required to operate at normal occupied design conditions in order to exhaust air from the conditioned space to the outdoors.

D. Exhaust system shall comply with all of the following:

The sum of the occupied minimum circulation rates of the spaces served by the fan system shall be less than 60 percent of the exhaust fan system design airflow rate.
The design exhaust fan system power shall not exceed 1.3 watts per cfm of exhaust fan system airflow when operating under full load design conditions.
The system shall include variable speed controls so that exhaust system fans shall draw no more than 40 percent of the design fan power when the exhaust fan system airflow is 60 percent of the design airflow rate.
The exhaust fan system airflow rate shall not exceed the larger of:
1. The sum of the space exhaust airflow rates served by the system, or
2. The minimum acceptable exhaust fan system airflow rate.
The minimum acceptable exhaust airflow rate, using the procedures and system definitions included in ANSI Z9.5 (2022) Appendix 3, shall be one of the following:
1. Less than 60 percent of the exhaust fan system design airflow rate (simple turndown control system), or
2. Dynamically reset based on measured wind speed and/or wind direction and assumes worst case emissions rate and shall be less than 60 percent of the exhaust fan system design airflow rate for at least 70 percent of the hours during a typical meteorological year (TY) for the site (wind responsive control system), or
3. Dynamically reset based on measured contaminant concentration and shall be less than 60 percent of the exhaust fan system design airflow rate when measured contaminants in the exhaust system plenum are below the threshold contaminant concentration value (monitored control system).
Exhaust system design and control results in calculated outdoor contaminant concentrations in compliance with applicable federal, state, or local regulations.
Applicable equipment and systems shall be certified as meeting the acceptance requirements for code compliance, as specified by the Reference Nonresidential Appendix NA7.16. A certificate of acceptance shall be submitted to the enforcement agency that certifies that the equipment and systems meet the acceptance requirements specified in NA7.16.

4. Fume Hood Automatic Sash Closure. Variable air volume laboratory fume hoods with vertical only sashes located in fume hood intensive laboratories, as described in Table 140.9-D, shall have an automatic sash closure system that complies with the following:

A. The automatic sash closure system shall be capable of the following:

i. The automatic sash closure system shall have a dedicated zone presence sensor that detects people in the area near the fume hood sash and automatically closes the sash within 5 minutes of no detection.

ii. The automatic sash closure system shall have controls to prevent the sash from automatic closing when a force of no more than 10 lbs is detected.

iii. The automatic sash closure system shall be equipped with an obstruction sensor that prevents the sash from automatic closing with obstructions in the sash opening. Obstruction sensor shall be capable of sensing transparent materials such as laboratory glassware.

iv. The automatic sash closure system shall be capable of being configured in a manual open mode where once the sash is closed, detection of people in the area near the fume hood by the zone presence sensor does not open the fume hood sash.

B. Fume Hood Automatic Sash Closure Acceptance. Before an occupancy permit is granted for the fume hoods subject to 140.9(c)4, the equipment and systems shall be certified as meeting the Acceptance Requirement for Code Compliance as specified by the Reference Nonresidential Appendix NA7. A Certificate of Acceptance shall be submitted to the enforcement agency that certifies that the equipment and systems meet the acceptance requirements specified in NA7.17.

Table 140.9-D Fume Hood Intensive Laboratories Threshold (both must be true)

Occupied Minimum Ventilation ACH	≤ 4	> 4 and ≤ 6	> 6 and ≤ 8	> 8 and ≤ 10	> 10 and ≤ 12	> 12 and ≤ 14
Hood Density (linear feet per 10,000 of laboratory space	≥ 6	≥ 8	≥ 10	≥ 12	≥ 14	≥ 16

5. Reheat Limitation. Air handlers in buildings with greater than 20,000 cfm of laboratory exhaust that serve multiple space conditioning zones in laboratory spaces shall not mechanically cool air handler supply air below 80 °F and shall not heat air handler supply air above 50 °F, and each zone shall include heating and cooling capacity, to prevent cooling at the air handler and reheating at the zones.

Exception 1 to Section 140.9(c)5: Additions or alterations to existing air handling systems serving existing zones without heating and cooling capacity.

Exception 2 to Section 140.9(c)5: Systems in climate zones 7 or 15.

Exception 3 to Section 140.9(c)5: Systems dedicated to vivarium spaces or to spaces classified as biosafety level 3 or higher.

Exception 4 to Section 140.9(c)5: Systems that:

1. Are located where the outdoor dew point temperature is greater than or equal to 64°F at the ASHRAE 2 percent annual dehumidification design condition, and

2. Include heating and cooling capacity at each zone, and

3. Do not mechanically cool air handler supply air below 80°F when the outdoor dew point temperature is below 60°F.

6. Exhaust Air Heat Recovery. Buildings with greater than 10,000 cfm of laboratory exhaust shall include an exhaust air heat recovery system that meets the following:

A. A sensible energy recovery ratio of at least 45 percent at heating design conditions and 25 percent at cooling design conditions.

B. Heat is recovered from at least 75 percent of all lab exhaust air volume.

C. The system includes a run-around coil pump or other means to disable heat recovery.

D. The system includes a bypass damper or other means so that the exhaust air pressure drop through the heat exchanger does not exceed 0.4 inch w.g. when heat recovery is disabled.

Exception 1 to Section 140.9(c)6: Additions or alterations to existing laboratory exhaust systems that do not include exhaust air heat recovery.

Exception 2 to Section 140.9(c)6: Buildings where the total laboratory exhaust rate exceeds 20 cfm/ft2 of roof area.

Exception 3 to Section 140.9(c)6: Locations that meet both of the following:

1. In Climate Zone 6 or 7; and

2. In a jurisdiction where gas heating is allowed.

Exception 4 to Section 140.9(c)6: Buildings with an exhaust air heat recovery system and heat recovery chillers designed to provide at least 40% of the peak heating load from exhaust heat recovery.

Exception 5 to Section 140.9(c)6: Exhaust systems requiring wash down systems such as exhaust systems dedicated to perchloric acid fume hoods.

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