§110.2(e)

There are mandatory requirements (§110.2[e]) for the efficient use of water in the operation of open (direct) and closed (indirect) cooling towers. The building standard applies to the new construction and retrofit of commercial, industrial, and institutional cooling towers with a rated capacity of 150 tons or greater. For these towers all of the following are required:

1. The towers shall be equipped with either conductivity or flow-based controls to manage cycles of concentration based on local water quality conditions. The controls shall automate system bleed and chemical feed based on conductivity, or in proportion to metered makeup volume, metered bleed volume, recirculating pump run time, or bleed time. Where employed, conductivity controllers shall be installed in accordance with manufacturer’s specifications.
2. Design documents have to document maximum achievable cycles of concentration based on local water supply as reported by the local water supplier, and using a calculator approved by the Energy Commission. The calculator shall determine maximum cycles based on a Langelier Saturation Index (LSI) of 2.5 or less. An approved calculator can be downloaded from the Energy Commission’s website: http://www.energy.ca.gov/title24/2019standards/documents/maximum_cycles_calculator.xls
3. The towers shall be equipped with a flow meter with an analog output for flow. This can be connected to the water treatment control system using either a hardwired connection or gateway.
4. The towers shall be equipped with an overflow alarm to prevent overflow of the sump in case of makeup water valve failure. This requires either a water level sensor or a moisture detector in the overflow drain. The alarm contact should be connected to the building Energy Management Control System to initiate an alarm to alert the operators.
5. The towers shall be equipped with drift eliminators that achieve a maximum rated drift of 0.002 percent of the circulated water volume for counter-flow towers and 0.005 percent for crossflow towers.

As water is evaporated off the tower, the concentration of dissolved solids, like calcium carbonate and silica, will increase. The pH of the water will also change. With high levels of silica, or dissolved solids, deposits will form on the tower fill or clog the tower nozzles, which will reduce the tower's heat rejection capacity. High pH is a concern for metal tower basins and structural members. As the thresholds of these contaminants of concern are approached the automated controls should bleed some of the concentrated water out and dilute it with make-up water. The bleed can be controlled by measurement of make-up water flow (an indirect measurement of water drift and evaporation) or through conductivity (a measurement of the dissolved solids). The term "cycles of concentration" is the metric of how concentrated the contaminants are at the controlled level. The right value depends on the characteristics of the supply water, the rate of tower drift, the weather characteristics, and the load on the tower. Good practice involves maintaining the following levels:

• Silica levels should be maintained at less than or equal to 150 ppm
• The Langelier Saturation Index should be maintained at less than or equal to 2.5 (see explanation below)
• The pH in new cooling towers using galvanized metal should be maintained at less than or equal to 8.3 until metal is passivated, which occurs after three-six months of operation

To meet compliance, an Energy Commission approved calculator (NRCC-MCH-06-E) allows the building owner to enter water quality parameters – including conductivity, alkalinity, calcium hardness, magnesium hardness, and silica. These values are available from the local water supplier in the most recent annual Consumer Confidence Report or Water Quality Report. These reports are generally posted on the water supplier’s website, or by contacting the local water supplier by telephone. Many water districts have multiple sources of water which often are changed seasonally. For example, many water districts use a reservoir in the winter and spring then switch to well water in the summer and fall. Each supply will typically have different characteristics; the water treatment and control cycles of concentration should be seasonally shifted as well.

After entering the required water quality data, the user must also enter skin temperature; the default value of 110 degrees F is acceptable. Lastly, target tower cycles of concentration are entered into the calculator. The calculator computes the LSI based on the cycles of concentration entered by the user. The maximum value of the index is 2.5. Therefore, the user should enter the highest cycles of concentration value in 0.10 units that results in a calculated LSI not to exceed 2.5. The resulting cycles of concentration are considered by the Energy Commission to be the Maximum Achievable Cycles of Concentration and must be recorded on the mechanical compliance document (NRCC-MCH-06-E), to which a copy of the Consumer Confidence Report or Water Quality Report must be attached. The professional engineer of record must sign the compliance document (NRCC-MCH-06-E) attesting to the calculated maximum cycles of concentration.

Example 4-41

Question

What is the Langelier Saturation Index?

Answer

The Langelier Saturation Index predicts scaling. It indicates whether water will precipitate, dissolve, or be in equilibrium with calcium carbonate. The index is a function of hardness, alkalinity, conductivity, pH, and temperature expressed as the difference between the actual system pH and the saturation pH.

Example 4-42

Question

Where is the data for makeup water quality?

Answer

Water agencies are required to make their annual water quality data available to the public. Water quality data is generally organized into an annual Consumer Confidence Report or Water Quality Report, which can often be found posted on the water agency’s website by searching for the key words “water quality”. Since many water districts have more than one water supply ask for a report for each source.

Example 4-43

Question

What if all, or some, of the water quality data is not provided in the Consumer Confidence Report or Water Quality Report?

Answer

Some data may be available by calling the local water agency’s Water Quality Division. For example, agencies are not required to test for and report alkalinity. However, they often do test for it and will provide data over the phone or in an email. Also check with water treatment firms that are doing business in the area. They often have test data that they will share. Finally, it is possible to hire a water treatment firm to take samples of the water to test.

§140.4(a)1 and §170.2(c)

The Energy Code requires mechanical heating and cooling equipment (including electric heaters and boilers) serving common use areas in multifamily buildings, hotel/motel buildings, and nonresidential buildings other than healthcare facilities to be the smallest size available, while still meeting the design heating and cooling loads of the building or spaces being served. Depending on the equipment, oversizing can be either a penalty or benefit to energy usage. For vapor compression equipment, gross oversizing can drastically increase the energy usage and in some cases cause premature failure from short cycling of compressors. Boilers and water-heaters generally suffer lower efficiencies and higher standby losses if they are oversized. On the other hand, cooling towers, cooling coils, and variable speed driven cooling tower fans can actually improve in efficiency if oversized. Oversized distribution ductwork and piping can reduce system pressure losses and reduce fan and pump energy.

When equipment is offered in size increments, such that one size is too small and the next is too large, the larger size may be selected.

Mechanical heating and mechanical cooling equipment serving healthcare facilities shall be sized to meet the design heating and cooling loads of the building or facility being served. Packaged HVAC equipment may serve a space with substantially different heating and cooling loads. The unit size should be selected on the larger of the loads, based on either capacity or airflow. The capacity for the other load should be selected as required to meet the load, or if very small, should be the smallest capacity available in the selected unit. For example, packaged air-conditioning units with gas heat are usually sized on the basis of cooling loads. The furnace is sized on the basis of airflow and is almost always larger than the design heating load.

Equipment may be oversized provided one or more of the following conditions are met:

1. It can be demonstrated (to the satisfaction of the enforcing agency) that oversizing will not increase building source energy use
2. Oversizing is the result of standby equipment that will operate only when the primary equipment is not operating. Controls must be provided that prevent the standby equipment from operating simultaneously with the primary equipment
3. Multiple units of the same equipment type are used, each having a capacity less than the design load. In combination, however, the units have a capacity greater than the design load. Controls must be provided to sequence or otherwise optimally control the operation of each unit based on load.

§140.4(a)2

   For prescriptive compliance the Energy Code requires single zone space conditioning systems with direct expansion cooling with rated cooling capacity 240,000 Btu/hr or less serving the following spaces to meet the following requirements.

1. Retail and Grocery Building Spaces in climate zones 2 through 15. The space conditioning system shall be a heat pump.
2. Retail and Grocery Building Spaces in climate zones 1 and 16 with cooling capacity less than 65,000 Btu/hr. The space conditioning system shall be an air conditioner with furnace.
3. Retail and Grocery Building Spaces in climate zones 1 and 16 with cooling capacity 65,000 Btu/hr or greater. The space conditioning system shall be a dual-fuel heat pump.
4. School Building Spaces. For climate zones 2 through 15, the space conditioning system shall be a heat pump. For climate zones 1 and 16, the space conditioning system shall be a dual-fuel heat pump.
5. Office, Financial Institution, and Library Building Spaces in climate zones 1 through 15. The space conditioning system shall be a heat pump.
6. Office, Financial Institution, and Library Building Spaces in climate zones 16 with cooling capacity less than 65,000 Btu/hr. The space conditioning system shall be an air conditioner with furnace.
7. Office, Financial Institution, and Library Building Spaces in climate zones 16 with cooling capacity 65,000 Btu/hr or greater. The space conditioning system shall be a dual-fuel heat pump.
8. Office Spaces in Warehouses. The space conditioning system shall be a heat pump in all climate zones.

Any space types not listed above are not subject to the requirements of §140.4(a)2, but shall comply with the other applicable requirements of §140. Also, all other system types, including systems with rated cooling capacity greater than 240,000 Btu/hr, multi-zone systems, and systems using central boilers or chillers, are not subject to the requirements of §140.4(a)2, but shall comply with the other applicable requirements of Section 140. For performance compliance, the prescriptive requirements in §140.4(a)2 set the standard design space conditioning budget. Under performance compliance the building can comply using any supported space conditioning system type as long as it meets the standard design source energy and TDV energy budgets for the building.

§140.4(b) and §170.2(c)2

For the purposes of sizing HVAC equipment, the designer shall use all of the following criteria for load calculations:

§140.4(c) and §170.2(c)4

Maximum fan power is regulated in individual fan systems where the power of at least one fan or fan array in the fan system is greater than or equal to 1kW of fan electrical input power at design conditions (see Section 4.10 for definitions). A system consists of only the components that must function together to deliver air to a given area; fans that can operate independently of each other comprise separate systems. Included are all fans associated with moving air from a given space-conditioning system to the conditioned spaces and back to the source, or to exhaust air to the outdoors.

The 1kW total criteria apply to:

The types of devices listed in Table 4-22 that qualify for additional fan power are as follows:

1. Return or exhaust systems required by code or accreditation standards to be fully ducted, or systems required to maintain air pressure differentials between adjacent rooms. The basic input power allowance is based on the assumption that return air passes through an open plenum on its way back to the fan system. For systems where all of the return air is ducted back to the return, an additional allowance equivalent to a pressure drop of 0.5 inches of water is allowed. This allowance may not be applied for air systems that have a mixture of ducted and non-ducted return.
2. Return and/or exhaust airflow control devices required for space pressurization control. Some types of spaces, such as laboratories, test rooms, and operating rooms, require that an airflow control device be provided at both the supply air delivery point and at the exhaust. The exhaust airflow control device is typically modulated to maintain a negative or positive space pressure relative to surrounding spaces. An additional pressure drop and associated input power adjustment are permitted when this type of device is installed. The allowance may be taken when some spaces served by an air handler have exhaust airflow devices and other spaces do not. However, the allowance is taken only for the cfm of air that is delivered to spaces with a qualifying exhaust airflow device.
3. Exhaust filters, scrubbers, or other exhaust treatment. Some applications require the air leaving the building be filtered to remove dust or contaminants. Exhaust air filters are also associated with some types of heat recovery systems, such as run-around coils. In this application, the purpose of the filters is to help keep the coils clean, which is necessary to maintain the effectiveness of the heat recovery system. When such devices are specified and installed, the pressure drop of the device at the fan system design condition may be included as an allowance. When calculating the additional input power, only consider the volume of air that is passing through the device under fan system design conditions.
4. Particulate filtration allowance: greater than MERV 16 and electronically enhanced filters. The primary purpose of filters is to keep the fans, coils, and ducts clean, and to reduce maintenance costs. A secondary purpose is to improve indoor air quality. MERV ratings are used as the basis of this allowance. These ratings indicate the amount of particulate removed from the airstream. A higher MERV rating is more efficient and removes more material. The allowance for filters with a MERV rating of 16 and greater and all electronically enhanced filters is based on two times the clean pressure drop of the filter at fan system design conditions. These clean pressure drop data are taken from manufacturers’ literature.
5. Carbon and other gas-phase air cleaners. For carbon and other gas-phase air cleaners, additional input power is based on the rated clean pressure drop of the air-cleaning device at fan system design conditions.
6. Biosafety cabinet. If the device is listed as a biosafety cabinet, you can use this allowance.
7. Energy recovery device. Energy recovery devices exchange heat between the outside air intake stream and the exhaust airstream. There are two common types of heat recovery devices: heat wheels and air-to-air heat exchangers. Both increase the pressure drop and require a system with a larger input power. The allowance increases linearly with an increasing energy recovery ratio. There are seven rows, but designers can only choose one allowance corresponding to their energy recovery device’s energy recovery ratio. The allowance is a function of the enthalpy recovery ratio. This is intended to encourage designers to select energy recovery devices that have low pressure drops and high enthalpy recovery ratios, and thus provide a net energy reduction. This allows systems that have trouble meeting the fan power limit to gain a higher fan power allowance — by using larger energy recovery devices with higher enthalpy recovery ratios.
8. Coil runaround loop. The coil runaround loop is a form of energy recovery device that uses separate coils in the exhaust and outdoor air intakes with a pump in between. The allowance is to account for the increased air pressure of these two coils.
9. Exhaust systems that serve fume hoods. Exhaust systems that serve fume hoods get an allowance equivalent to an additional 0.35 inches of water to account for the pressure through the fume hood, ductwork, and zone valve or balancing devices. This allowance applies to the exhaust fans only.

Example 4-45

Question

A multi zone VAV reheat system serves a low-rise office building. The building is served by one VAV packaged rooftop unit with a 10 hp supply fan with a VSD. There is a separate return fan, also with a VSD. Four parallel fan-powered VAV terminal units are used on north-facing perimeter offices for heating. Two series fan-powered VAV boxes, each with a 1/3 hp fan with an electronically commutated motor, serve two interior conference rooms.

The space also uses a local exhaust fan for each of the four bathrooms. Fans for the system are listed below. Fan performance is as described in the table below. The fan electrical input power was calculated using motor and VFD (where applicable) efficiency assumptions derived from AMCA 207, which is one of the methods to convert shaft brake horsepower to input electrical power available to designers. The motors were assumed to be 4-pole ODP (open drip proof) with direct drive transmission.

Is this system in compliance with Section 140.4(c)?

Answer

First, determine which fans to include in the nameplate fan system power calculation:

• The supply and return fans are clearly included in the fan power calculation.
• The condenser fans are not included because they circulate outdoor air and do not affect the conditioned air supplied to the space.
• The toilet exhaust fans are included because they each have a fan electrical input power of less than 1 kW.
• The parallel fan powered and series fan-powered VAV boxes are not included in the fan power calculation because they each have a fan electrical input power of less than 1kW. However, the deduction for terminal units < 1 kW will be applied to the series fan-powered boxes. The deduction does not apply to the parallel boxes because their fans do not operate at design conditions.

There are two steps to determine whether the fan system complies with the fan power budget. First, the allowable power must be calculated. Second, the fan electrical power input of the in-scope fans must be compared to the allowable budget to determine if the system complies.

The fan system is a multi-zone VAV fan type, with an airflow greater than 10,000 cfm. Therefore, W/cfm values from the third column from the left from Tables 140.4-A and Table 140.4-B are used. The applicable supply side allowance (taken from Table 140.4-A) for this system type (i.e., a multi-zone VAV system greater than 10,000 cfm) are summarized in the table below.

*This value must be adjusted to reflect airflow passing through the VAV boxes

The following formula is used to adjust the terminal unit deduction.

The adjusted fan power allowance for each parallel fan powered VAV box is show below.

Series FPAadj = (2* 600 / 12,000) x (-0.100) = -0.010

Taking this adjustment into account, the total supply side power allowance is 0.718 W/cfm, and at 12,000 cfm, this is 8.62 kW.

The return fan system only qualifies for the base allowance, which is 0.236 W/cfm. At 11,000 cfm, this is 2.60 kW.

The supply and return fan systems are evaluated separately since the return fan is not in the same cabinet as the supply fan.

The actual supply-only fan system total electrical power input is 7.35 kW, so this fan system complies with Section 140.4(c). The proposed return fan system exceeds the allowance of 2.60 kW, so does not comply.

Example 4-46

Question

A conventional VAV system serves an office building. Fan performance is as described in the table below. Is the system in compliance with Section 140.4(c)?

Answer

First, determine which fans to include in the fan power calculation:

• Supply fans are included.
• The economizer relief fans are not included because they will not operate at peak cooling design conditions. Had return fans been used, they would have to be included in the calculation.
• The toilet exhaust fan is included because it exhausts conditioned air from the building rather than have it returned to the supply fan, and it operates at peak cooling conditions.
• The elevator exhaust fan is not part of the system because it is assumed, assumed that the fan consumes less than 1 kW of input electrical power (even though the bhp is not available, the maximum electrical input power for fans with a motor hp < 1 is 0.89 from Table 140.4-D).
• The cooling tower fans operate at design conditions, but they also are not part of the system because they circulate only outdoor air. Although the cooling tower fan power does not contribute to the system fan power, it is required to meet the minimum efficiency requirements in Table 110.2-G.
• The conference room exhaust and series-type fan-powered VAV boxes are not included because they consume less than 1 kW each. However, the terminal unit deduction will be applied for the VAV boxes, as explained below.

Second, calculate the allowable fan power budget. The applicable allowances are shown in the table below. The system is assumed to be a single cabinet fan system. The allowances are from the >10,000 cfm multi-zone VAV column of Table 140.4-A and Table 140.4-B.

The exhaust system base allowance is included since this is being treated as a single cabinet fan system.

In order to calculate the appropriate deduction for the fan-powered VAV boxes, the following procedure is to be followed.

The adjusted fan power allowance for each parallel fan powered VAV box is show below.

FPAadj = (1,250 / 150,000) x (-0.100) = -0.0008333

Given that there are 120 fan powered VAV boxes, the total deduction is calculated below.

Terminal unit FPAadj = 120 x FPAadj = -0.100 W/cfm

Note that this is the same value as the initial deduction since all of the supply airflow passes through the 120 VAV boxes.

The allowances add up to 0.864 W/cfm, which, when multiplied by 150,000 cfm yields 129.60 kW.

The bathroom exhaust fan is also in-scope, and its allowance is calculated using the exhaust system base allowance (0.236 W/cfm) multiplied by the airflow (6,750 cfm), which yields 1.59 kW.

The total power allowance is 131.19 kW. The actual input power of the in-scope fans is 115.88 kW (this includes the two supply fans and the toilet exhaust fan), so this system meets the requirements of Section 140.4(c). If the system did not comply, the designer could consider using larger ducts to reduce static pressure.

Example 4-47

Question

A hotel/motel building has floor-by-floor supply air-handling units but central toilet exhaust fans and minimum ventilation supply fans. How is the standard applied to this system?

Answer

Each air handler is as a single-cabinet fan system, the central ventilation fan is a supply-only system, and the central exhaust is an exhaust system. Each fan system is evaluated separately.

Example 4-48

Question

A wing of an elementary school building is served by eight water-source heat pumps, each equipped with a 3/4 hp fan motor and serving a single classroom. Ventilation air is supplied directly to each classroom by a dedicated outdoor-air system. Each classroom requires 500 cfm of outdoor air, so the system delivers the total of 4000 cfm of conditioned outdoor air using a 5 hp fan. Does this system need to comply with Section 140.4(c)?

Answer

The water-source heat pumps are not counted since their motors consume less than 1 kW. The dedicated outdoor-air system fan, which consumes more than 1 kW, is evaluated on its own. If the outdoor air is passes through the fans of the water-source heat pumps, the 0.100 w/cfm deduction in Table 140.4-A would be applied.

Example 4-49

Question

A variable-volume air handler serving a lab system at 4,400 feet altitude has a fan system design supply airflow of 10,000 cfm. The supply fan has a 15 hp (nameplate) supply fan motor that operates at an input power of 10.7 bhp. The return fan is in the same cabinet as the supply fan and has a three hp motor that operates at an input power of 2.5 bhp. The system has hydronic heating and cooling coils. Flow control devices in the exhaust are used to maintain pressure relationships between spaces served by the system.

The air handler uses MERV 13 filters and exhaust air is completely ducted. The system uses outdoor air and has a run-around heat recovery system with coils in the supply and exhaust airstreams, each with 0.4 in. of water pressure drop at design airflow.

Does this fan system comply with the fan power requirements in Section 140.4(c)?

Answer

This system is treated as a single-cabinet fan system. The correct column from which to select allowances is “multi-zone VAV systems >5,000 and ≤10,000 cfm.” The altitude correction factor will need to be applied to the fan power allowance once all allowances are summed up. The allowable allowances for the supply and return sides are shown in the tables below.

The grand total for all allowances is 0.881 + 0.446 = 1.327 W/cfm, however, this value must be multiplied by the altitude correction factor to account for reduced air density, found in Table 140.4-C. Since the building is at 4,400 ft elevation, the applicable factor is 0.864. The resulting corrected power allowance is 1.327 W/cfm x 0.864 = 1.147 W/cfm.

The final step is to multiply the power allowance rate by the system airflow, as shown below.

Allowable power = 1.147 W/cfm x 10,000 cfm / 1,000 W/kW = 11.47 kW.

The fan electrical input power can be calculated using the provided fan brake horsepower values along with AMCA 207 to estimate transmission, motor, and motor controller losses. Assuming both motors are direct drive, have a motor controller, are ODP, and are 4-pole motors, the supply fan input power is 8.89 kW, and the return fan input power is 2.29 kW, for a total of 11.18 kW. Therefore, this system meets the requirements of Section 140.4(c).

Exhaust airstream has a MERV 8 filter. The system requires 0.50” w.c. of external static pressure and consumes 2.85 kW at design conditions, as provided by the manufacturer. Does the system comply with Section 140.4(c)?

Answer

Since this system does not meet the definition of “multi zone VAV”, the allowance will be selected from the “all other systems ≤ 5,000 cfm” column. The system will be treated as a single cabinet fan system. The applicable allowance is displayed in the table below.

For a 3,000 cfm system, this results in an allowable power of (1.254 W/cfm) x (3,000 cfm) / (1,000 W/kW) = 3.76 kW. Since the system power consumption is 2.85 kW, this system meets the requirements of Section 140.4(c).

§140.4(c)4 and §170.2(c)Aiii

HVAC fan motors that are one hp or less and 1/12 hp or greater shall be electronically commutated motors or shall have a minimum motor efficiency of 70 percent when rated in accordance with the National Electric Manufacturers Association (NEMA) Standard MG 1-2006 at full-load rating conditions. These motors shall also have the means to adjust motor speed for either balancing or remote control. Belt-driven fans may use sheave adjustments for airflow balancing in lieu of a varying motor speed.

This requirement can be met with either electronically commutated motors or brushless direct current (DC) motors. These motors have higher efficiency than permanent split capacitor (PSC) motors and inherently have speed control that can be used for VAV operation or balancing.

This requirement includes fan-powered terminal units, fan-coil units, exhaust fans, transfer fans, and supply fans. There are three exceptions to this requirement:

1. Motors in fan-coil units and terminal units that operate only when providing heating to the space served. This includes parallel style fan-powered VAV boxes and heating only fan-coils.
2. Motors that are part of space conditioning equipment certified under §110.1 or §110.2. This includes supply fans, condenser fans, ventilation fans for boilers, and other fans that are part of equipment that is rated as a whole.
3. Motors that are part of space conditioning serving healthcare facilities.

§140.4(g), §141.0, and §170.2(c)4E

The Energy Code strongly discourage the use of electric-resistance space heat. Electric-resistance space heat is not allowed in the prescriptive approach except where:

§140.4(h)3 and §170.2(c)4Fii

The Energy Code requires that open cooling towers with multiple condenser water pumps be designed so that all cells can be run in parallel with the larger of the flow that is produced by the smallest pump or 50 percent of the design flow for the cell.

In a large plant at low load operation, not all the cells are typically run at once. This is allowed in the Energy Code.

Cooling towers are very efficient at unloading the fan energy drops off as the cube of the airflow. It is always more efficient to run the water through as many cells as possible- two fans at half speed use less than one third of the energy of one fan at full speed for the same load. Unfortunately, there is a limitation with flow on towers. The flow must be sufficient to provide full coverage of the fill. If the nozzles do not fully wet the fill, air will go through the dry spots providing no cooling benefit and cause the water at the edge of the dry spot to flash evaporate, depositing dissolved solids on the fill.

Fortunately, the cooling tower manufacturers do offer low-flow nozzles (and weirs on basin type towers) to provide better flow turndown. This typically only costs $100 to $150 per tower cell. As low-flow nozzles can eliminate the need for a tower isolation control point, this option provides energy savings at a reduced first cost.

Example 4-51

Question

If a large central plant has five equally sized chillers and five equally sized cooling tower cells do all of the cooling tower cells need to operate when only one chiller is on-line?

Answer

No. You would probably only run three cells with one chiller. The cooling tower cells must be designed to run at 33 percent of their nominal design flow. With two to five chillers running, you would run all of the cells of the cooling tower. With only one chiller running you would run three cells. In each case, you would need to keep the tower flow above the minimum that it was designed for.

§140.4(h)4 and §170.2(c)4Fiii

Open cooling towers with a combined rated capacity of 900 gpm and greater are prohibited from using centrifugal fans. The 95-degree F condenser water return, 85-degree F condenser water supply and 75-degree F outdoor wet-bulb temperature are test conditions for determining the rated flow capacity in gpm. Centrifugal fans use approximately twice the energy as propeller fans for the same duty. There are a couple of exceptions to this requirement:

1. Cooling towers that are ducted (inlet or discharge) or have an external sound trap that requires external static pressure capability.
2. Cooling towers that meet the energy efficiency requirement for propeller fan towers in Table 4-7.

Centrifugal fans may be used on closed circuit fluid coolers.

As with all prescriptive requirements centrifugal fan cooling towers may be used when complying with the performance method. The budget building will be modeled using propeller towers.

§140.4(h)5 and §170.2(c)4Fv

Prescriptively, axial fan open-circuit cooling towers with a combined rated capacity of 900 gpm or greater must achieve a rated efficiency no less than 60 gpm/hp. This efficiency is rated at specific temperature conditions which are 95-degree F condenser water return; 85-degree F condenser water supply; and 75-degree F outdoor wet-bulb temperature as listed in Table 4-7. There are a couple of exceptions to this requirement:

1. Cooling towers that are installed as a replacement to an existing chilled water plant if the tower is located on an existing roof or inside an existing building.
2. Cooling towers that are serving buildings in Climate Zones 1 or 16.

As with all prescriptive requirements, axial-fan open-circuit cooling towers with a capacity of 900 gpm or larger and less than 60 gpm/hp may be used when complying with the performance method. The towers must still comply with the mandatory minimum efficiency rating of 42.1 gpm/hp as listed in Table 4-7.

§140.4(i) and §170.2(c)4G

In Table 4-4, there are two sets of efficiency for almost every size and type of chiller. Path A represents fixed speed compressors and Path B represents variable speed compressors. For each path, there are two efficiency requirements: a full load efficiency and an integrated part-load efficiency. Path A typically has a higher full load efficiency and a lower part-load efficiency than Path B. In all California climates, the cooling load varies enough to justify the added cost for a Path B chiller. This is a prescriptive requirement, so Path B is used in the base case model in the performance method.

There are a number of exceptions provided to this requirement:

1. Chillers with an electrical service of greater than 600 volts. This is due to the fact that the cost of a VSD is much higher on medium voltage service.
2. Chillers attached to a heat recovery system with a design heat recovery capacity greater than 40 percent of the chiller's design cooling capacity. Heat recovery typically requires operation at higher lifts and compressor speeds.
3. Chillers used to charge thermal energy storage systems with a charging temperature of less than 40 degrees F. This again requires a high lift operation for chillers.
4. In a building with more than three chillers only three are required to meet the Path B efficiencies.

§140.4(j), §141.0, and §170.2(c)4G

New central cooling plants and cooling plant expansions will be limited on the use of air-cooled chillers. For both types the limit is 300 tons per plant.

In the studies provided to support this requirement, air cooled chillers always provided a higher life cycle cost than water-cooled chillers even accounting for the water and chemical treatment costs.

Exceptions to this requirement:

1. Where the water quality at the building site fails to meet manufacturer’s specifications for the use of water-cooled chillers.
   This exception recognizes that some parts of the state have exceptionally high quantities of dissolved solids that could foul systems or cause excessive chemical treatment or blow down.
2. Chillers that are used to charge a thermal energy storage system with a design temperature of less than 40 degrees F.
   This addresses the fact that air-cooled chillers can operate very efficiently at low ambient air temperatures. Since thermal energy storage systems operate for long hours at night, these systems may be as efficient as a water-cooled plant. The chiller must be provided with head pressure controls to achieve these savings.
3. Air cooled chillers with minimum efficiencies approved by the Energy Commission pursuant to §10-109(d).
   This exception was provided in the event that an exceptionally high efficiency air cooled chiller was developed. None of the high-efficiency air-cooled chillers currently evaluated are as efficient as water-cooled systems using the lowest chiller efficiency allowed by §110.2.
4. Systems serving healthcare facilities.

§140.4(o) and §170.2(c)4M

The standard prescriptively requires the use of transfer air for exhaust air makeup in most cases. The purpose is to avoid supply air that requires increased outdoor air intake, which would require conditioning, for exhaust makeup when return or relief air from neighboring spaces can be used instead. The requirement limits the supply of conditioned air to not exceed the larger of 1.) the supply flow required for space heating or space cooling, 2.) the required ventilation rate, or 3.) the exhaust flow, minus the available transfer air from conditioned spaces or plenums on the same floor and within 15 ft and not in different smoke or fire compartments. Available transfer air does not include air required to maintain pressurization and air that cannot be transferred based on-air class as defined by in §120.1.

There are a few exceptions to this requirement:

1. Biosafety laboratories classified Level 3 or higher
2. Vivarium spaces
3. Spaces that are required by applicable codes and standards to be maintained at positive pressure relative to adjacent spaces. For spaces taking this exception, any transferable air that is not directly transferred shall be made available to the associated air-handling unit and shall be used whenever economizer or other options do not save more energy.
4. Spaces where the demand for transfer air may exceed the available transfer airflow rate and where the spaces have a required negative pressure relationship. For spaces taking this exception, any transferable air that is not directly transferred shall be made available to the associated air-handling unit and shall be used whenever economizer or other options do not save more energy.
5. Healthcare facilities

A compliant example would be a space with a restroom with 300 cfm of exhaust. The makeup air would consist of 60 cfm of supply air and 240 cfm of transfer air from an adjacent ceiling return air plenum. The amount of air required for the space is 60 cfm for heating and cooling and the rest of the makeup air is transferred from the return air plenum.

A non-compliant example would be if the same space had a constant air volume box with reheat supplying all of the makeup air. The reheat would be needed to prevent the space from being overcooled. Since there is transfer air available in the adjacent plenum, the maximum allowed supply air would be only what’s required for space heating or cooling, which would be 60 cfm.