Table of Contents
A cold storage critical-load list starts with the rooms and processes that must be supported, then identifies their electrical equipment. Compressors, auxiliary equipment, controls and temperature monitoring need to form a functioning group. Adding nameplate kilowatts without those relationships does not provide enough information to select backup power.
The practical output is a register. Every load has an identifier, electrical characteristics, operating pattern, dependencies and someone responsible for confirming the data. The example below shows how to build and check that register. Calculating electricity use does not establish a safe storage period for the goods.
Define the temperature requirement for each zone
List rooms, product types, storage requirements, sensor locations and responsible personnel. Distinguish maintaining already chilled goods from cooling a new delivery or freezing products. These impose different duties on the refrigeration plant, even within the same room.
Each zone needs agreed temperature limits, a procedure for assessing excursions and staff actions. The responsible team establishes these against the requirements for the actual goods and process. Room air, evaporator sensor readings and product temperature are different measurements. The register should identify what is being monitored.
Specify electrical backup duration separately. Two hours of power for selected loads does not mean a two-hour cooling interruption is acceptable. Loading, door openings and outdoor conditions require site evidence. Do not expose inventory to risk simply to obtain a temperature-rise curve.
Map rooms to equipment and shared services
Trace each required zone to its cooling source, circulation, heat rejection and controls. Identify compressors, condenser and evaporator fans, pumps where fitted, valves, controllers and their power supplies. Show shared equipment relationships on one schedule.
Use identifiers consistently across the register, electrical drawing and measurement log. For example, C1 and C2 denote compressors, F1 the condenser group, F2 room fans and A0 controls. A group serving several rooms must not be counted separately for each room.
Add easily overlooked loads: heaters, defrost, drainage, communications, recorders and necessary lighting. Check site safety and alarm systems too. They cannot be excluded simply because they do not produce cooling. An unexplained entry marked “other” is unsuitable for the final list.
Give every load a record and every figure an origin
Each register entry should identify the load, zone, quantity, switchboard and supply circuit. Record voltage, phases, operating electrical power, phase currents and, where required to assess the source, apparent power in kVA. Refrigeration capacity is not a substitute for electrical input power.
Provide separate fields for starting method, starting current and duration, allowable interruption, restart conditions and dependent equipment. Identify each value as a model-specific specification, measurement or assumption. Include the date, operating conditions and the corresponding file in the business's internal records.
Hypothetical C1 record: compressor serving the agreed rooms; three-phase supply; assumed 12 kW electrical input for this example; dependencies A0, F1 and the relevant part of F2. Apparent power, starting requirements and allowable interruption remain “confirmation required”. This is an honestly completed preliminary entry, but insufficient for selecting an inverter or generator.
An empty field is not zero. Assign missing information to the electrical team, refrigeration team or equipment manufacturer. A nameplate photograph identifies equipment but does not describe every operating condition.
Related F1 record: a shared condenser group serving C1 and C2, with an assumed 2 kW input. Reference it in both compressor records but count its energy once, using its own schedule. Removing a room from backup does not necessarily remove its shared services. Deleting a row without checking dependencies can leave a numerically correct but incomplete system.
Measure the conditions that change demand
Match electrical logs with temperatures, loading, door openings and defrost cycles. Separate temperature maintenance, goods reception, intensive cooling and recovery after interruption. A quiet overnight measurement does not represent a warm delivery arriving at the warehouse.
Energy assessment needs a time profile. Starting assessment needs a separate event recording with sufficient resolution to capture a short transient. Interval averages can conceal current peaks. Qualified personnel should agree the measurement method, instrument location and work at electrical panels.
Record whether equipment operates at full or partial capacity, which fans run and which interlocks are active. For a new warehouse, label design assumptions separately. Compare them with actual equipment and agreed tests before accepting the backup installation.
Check the time zone and clocks of the recorder, controller and meter. Identify gaps and manual operating changes. Mismatched timestamps can create a false relationship between a temperature event and a compressor start. Retain raw data and the processing explanation so another specialist can reproduce the conclusion.
Prioritize functions rather than motor size
First identify control, protection and notification circuits requiring continuity or a short permitted interruption. Then define refrigeration groups that may cycle under an agreed sequence. List deferrable activities separately, with approval from those responsible for the process and safety.
Priority does not mean unconditional permission to start. For each group, record enabling conditions, reasons for inhibition and readiness confirmation. A high-priority compressor still requires the manufacturer's supporting systems and protections. Bypassing interlocks to reduce demand is not a backup operating mode.
Assess defrost, heaters and pumps for the particular installation. Do not label them deferrable merely because this lowers the total. If postponement has not been approved, retain the scenario as an unresolved item for the refrigeration specialist.
Describe restart as a separate scenario
Each compressor needs information about its actual starter or variable-frequency drive and permitted starting conditions. A universal multiplier on running kilowatts is insufficient. Check current, duration, loads already operating and the backup source's response to the transition.
Describe events: control power returns, auxiliary readiness is checked, the first group receives permission and stable operation is confirmed before the next group. Obtain actual delays from the installation documentation and settings. Do not shorten compressor protection delays simply to accelerate cooling.
Check controller behavior after reboot as well. Defrost timing may restart or temperature alarms may be delayed. A live switchboard does not establish that cooling has resumed or that the duty operator received a notification. Record separate outcomes for electrical supply, refrigeration and alarms.
Show energy and simultaneous demand in one example
Every figure below is invented. The calculation covers two hours, with powers defined at the loads. Operating time is the accumulated running time within that window, not an allowable interruption. For arithmetic, assume an agreed schedule without an electric defrost cycle. Its suitability for any real warehouse has not been established.
| Identifier and group | Running kW | Operating hours | Energy, kWh |
|---|---|---|---|
| A0: controls and recording | 0.4 | 2 | 0.8 |
| C1: first compressor | 12 | 1.25 | 15 |
| C2: second compressor | 12 | 0.5 | 6 |
| F1: condenser group | 2 | 1.5 | 3 |
| F2: room fans | 1.2 | 2 | 2.4 |
| L1: agreed auxiliary circuits | 0.6 | 2 | 1.2 |
| Total | 28.2 | Not added | 28.4 |
Total energy is 0.8 + 15 + 6 + 3 + 2.4 + 1.2 = 28.4 kWh. Average demand is 14.2 kW. When A0 + C1 + C2 + F1 + F2 + L1 operate together, their running demand is 28.2 kW. Starting a load while others already run requires a separate assessment.
One possible steady-state schedule has both compressors running for the first 15 minutes, C1 alone for the next 60, C2 alone for another 15 and neither for the final 30. F1 runs for the first 90 minutes; A0, F2 and L1 run throughout. Interval demands are 28.2, 16.2, 16.2 and 2.2 kW. This explains simultaneity, without instructing simultaneous starts. Transients and cooling adequacy have not been calculated.
An additional hypothetical 6 kW heater running for 15 minutes adds 1.5 kWh, bringing energy to 29.9 kWh. Its coincidence with compressor operation depends on the control sequence; it cannot automatically be added to the peak. The handbook explains storage power and energy capacity. The calculated 28.4 kWh is neither a battery nameplate capacity nor a temperature guarantee.
Check the register during source transfers
Give the engineer scenarios for grid loss, transfer to backup, exhaustion of available reserve and restoration of normal supply. Each needs permitted groups, interruptions, signals and recovery steps. Where a generator exists, include its load acceptance capabilities and planned battery charging.
Agree tests with refrigeration personnel and the team responsible for the goods. Record the actual sequence, currents, controller events, temperatures and notifications. Starting one compressor successfully does not verify every scenario. Define test stopping conditions beforehand.
Hand over a controlled set of inputs
Attach zone plans, electrical drawings, equipment documents, measurement files and approved operating descriptions. Keep unresolved starting, temperature, defrost and shared-service questions visible. Date each revision and identify its owner. Replacing equipment or changing stored goods requires reviewing the inputs.
Give suppliers the same register version. An offer covering controls and fans cannot have its backup duration compared directly with one also supporting compressors. Request explicit load identifiers, exclusions and conditions behind the proposed performance.
To discuss backup power for a cold storage warehouse, send this package to ONG Solar. It supports checking the critical group and defining the selection task. The configuration follows verification of actual site data, compatibility and operating requirements.