## 13.18. NA7.5.14 Thermal Energy Storage (TES) System Acceptance

At-A-Glance

NA7.5.14 Thermal Energy Storage (TES) System Acceptance
Use Document NRCA-MCH-15-A
Purpose of the Test
This test verifies proper operation of thermal energy storage (TES) systems. TES systems reduce energy consumption during peak demand periods by shifting energy consumption to nighttime. Operation of the thermal energy storage compressor during the night produces cooling energy, which is stored in the form of cooled fluid or ice in tanks. During peak cooling hours the thermal storage is used for cooling to prevent the need for chiller operation.
Benefits of the Test
The test will ensure that the TES system is able to charge the storage tank during off-peak hours and conversely discharge the storage tank during on peak hours. Since the chiller may operate more efficiently at night when ambient temperatures are lower, the system may save cooling energy in some climate zones.
Instrumentation
TES acceptance tests require no additional instrumentation for testing.
Test Conditions
The chiller, EMS, piping, and components should be installed and operational. The thermal storage tank should be without charge, or even partially charged (not fully charged), at the start of testing. The system should be configured with an on-peak cooling period (tank discharge) and an off-peak charging period. The cooling load can be met by storage if the tank has stored energy available or by compressor cooling if there is no stored energy available.
Estimated Time to Complete
Construction Inspection: 0.5 hours
Acceptance Tests: 2 hours
Acceptance Criteria
The TES system and the chilled water plant is controlled and monitored by an EMS. Verify: The TES system stores energy in storage/charge mode. The storage charging stops when an end of charge signal is generated. The TES system starts discharging with the compressor(s) in discharge mode. The TES does not discharge and the cooling load is met by the compressor(s) in mechanical cooling only mode. The TES discharges with the chiller sharing the load during discharge and mechanical cooling mode. Storage does not discharge and all compressors are off during the off/storage-secure mode. When applicable, tanks can be charged while serving in active cooling mode during charge-plus cooling mode.
Potential Problems and Cautions
Potential damage to the chiller, pumps, storage tanks, etc., by improper manipulation of the control system. Perform this test with the assistance of the controls vendor or facility operator.

A. Test Application

Newly Constructed and Additions/Alterations: Applies to thermal energy storage systems used in conjunction with chilled water air conditioning systems.

B. Construction Inspection

Verify that the efficiency of the chiller meets or exceeds the requirements of §110.2.

Supporting documentation needed to perform the test includes:

• Construction documents (plans, drawings, equipment schedule, etc.)

• Approved submittals (for chillers, storage tanks, controls)

• Copy of manufacturers’ product literature

• Copy of the Building Energy Efficiency Standards and Appendices

System Installation Information

The following information for both the chiller and the storage tank(s) shall be provided on the plans to document the key TES System parameters.

1. Chiller(s)

• Manufacturer Brand and Model

• Type (Centrifugal, Reciprocating, etc) and quantity

• Heat rejection type (air, water, other)

• Charge mode capacity (tons) at average fluid temperature

• Discharge mode capacity (tons) at temperature

• Discharge mode efficiency (kW/ton or EER) at design ambient temperature

• Charge mode efficiency at nighttime design ambient temperature (kW/ton or EER)

• Fluid type and percentage (nameplate)

2. Storage

• Type (Ice-on-Coil Internal Melt, Ice-on-Coil External Melt, Encapsulated (e.g. ice balls), Ice Harvester, Ice Slurry, Other Phase Change Material (e.g. paraffin), Chilled Water, Brine (or chilled water with additives), Eutectic Salt, Clathrate Hydrate Slurry (CHS) Cryogenic, Other (specify)

• Brand and Model

• Number of Tanks

• Height/width/depth, or height/diameter (if custom tanks)

• Storage capacity per tank (ton-hours) at entering/leaving temperatures and hours discharged

• Storage rate (tons) at flow rate (gpm) per tank

• Minimum charging temperature based on chiller and tank selections

• Discharge rate (tons) at entering/leaving temperatures and hours discharged

C. Functional Testing

Step 1: TES System Design Verification

The installing contractor(s) shall certify the following information, which verifies proper installation of the TES system components, consistent with system design expectations.

• Chiller(s) start-up procedure has been completed

• System fluid test and balance has been completed

• Air separation and purge has been completed

• Fluid (e.g. glycol) has been verified at the concentration and type indicated on the design documents

• The TES system has been fully charged at least once and charged duration noted

• The system has been partially discharged at least once and discharged duration noted

• The system is in partial charge state in preparation for Step 2

• Schedule of operation has been activated as designed

• Mode documentation describes the state of system components in each mode of operation

Step 2: TES System Controls and Operation Verification

The Acceptance Testing Technician shall verify the following information:

1. The TES system and the chilled water plant is controlled and monitored by an EMS.

2. The system has controls in place configured for the operator to manually select each mode of operation or use an EMS schedule to specify the mode of operation.

3. The scheduled operations listed below, not the times when the system will be in each mode of operation:

• Storage/charge mode. Manually select storage mode. Verify that the TES system stores energy. If the TES operates on a schedule, note the times, what causes the TES to engage, and that the TES system enters energy storage mode.

• End of charge signal. Simulated a full storage charge by changing the thermal storage manufacturer’s recommended end of charge output sensor to the EMS. Verify that the storage charging stops.

• Discharge Mode. Simulate a call for cooling. Manually select storage only discharge mode. Verify that the TES system starts discharging with the compressors off. Return to the off/secured mode. If the TES operates on a schedule, note times, what causes the TES to engage, and that the TES system starts discharging with the compressor(s) off.

• Mechanical cooling only mode. Simulate a call for cooling. Manually select mechanical cooling only mode and verify that the storage does not discharge and the cooling load is met by the compressor(s) only. Return to the off/secured mode. If the TES operates on a schedule, not the times, what causes the TES to engage, and that the storage does not discharge and the cooling load is met by the compressor(s) only.

• Discharge and mechanical cooling mode. Simulate a call for cooling. Manually select discharge and mechanical cooling mode. Verify that the TES system discharges with the chiller(s) sharing the load. Return to the off/secured mode. If the TES operates on a schedule, not the times, cause the TES to engage, and verify that the storage starts discharging with the compressor(s) sharing the load.

• Off/storage-secured mode. Manually select the off/storage-secured mode. Verify that the storage does not discharge and all compressors are off. If the TES operates on a schedule, note the times, what causes the TES to engage, and that the storage does not discharge and all compressor(s) are off, regardless of the presence of calls for cooling.

• Charge plus cooling mode If the provisions for this mode have been made by the system designer, verify that the tank(s) can be charged while serving an active cooling load, simulated by generating a call for cooling and entering the charge mode either manually or by time schedule. If the system disallows this mode of operation, verify that energy storage is disallowed or discontinued while an active cooling load is present.