RECDs for Cold Storage Facilities: Assessing Refrigeration Load Patterns

A cold store does not draw power the way an office block or a factory shift does. Its demand climbs hard after fresh produce arrives, settles for weeks, jumps during defrost, and swings with the outdoor temperature. The DG set that backs it up sees every one of those swings.

That matters when you fit a retrofit emission control device. An RECD for cold storage works best when the generator’s exhaust stays hot enough, long enough, for the filter to clean itself. Whether that happens depends far more on your refrigeration load pattern than on the brochure.

This guide treats the decision as an engineering load assessment: understand the load, log it, then decide.

Why Load Pattern Decides RECD Success

A typical RECD pairs a diesel oxidation catalyst (DOC) with a diesel particulate filter (DPF). The DOC oxidises carbon monoxide and hydrocarbons and converts some nitric oxide to nitrogen dioxide. The DPF traps soot. If you want the basics first, our explainer on what an RECD is and how it works covers the hardware.

The trapped soot has to go somewhere. In passive regeneration, the NO2 from the catalyst and the heat of the exhaust burn the soot off continuously. That only happens when exhaust temperature is high enough, which generally needs meaningful engine load. Figures of around 40 to 50% load or higher are often cited, though the exact threshold depends on the filter design, the coating and the engine.

Here is the chain of cause and effect that every cold store manager should understand:

1. Light load means cool exhaust. A diesel engine at 20% load produces exhaust far cooler than the same engine at 70%.
2. Cool exhaust means slow or no regeneration. Soot accumulates faster than it burns.
3. Soot loading raises backpressure. The engine has to push exhaust through a progressively clogged filter.
4. High backpressure hurts the engine. Fuel use rises, power can drop, and turbocharger and exhaust components work harder. Our post on how exhaust backpressure affects a DG set explains the limits engine makers set.
5. Light running also causes wet stacking. Unburnt fuel and oil collect in the exhaust, adding to the deposit problem.

So the question is not simply “will an RECD fit our 500 kVA set?” It is “how many hours a month does our set run above the load where the filter cleans itself, and how many hours does it spend below?”

Anatomy of a Cold Store’s Electrical Load

Before you can judge load pattern, you need to know what is drawing the power. A cold store is a collection of very different loads, some steady and some spiky.

Compressors

Compressors are the heaviest consumers, often well over half the connected load. Older and smaller stores tend to use reciprocating compressors, sometimes several of them in parallel on ammonia or freon systems. Larger plants increasingly use screw compressors, which handle part load through slide valve unloading or variable speed drives.

How the compressors are controlled shapes the DG’s experience. Multiple reciprocating machines staged on and off create step changes in load. A screw compressor unloading to 30% capacity still draws a meaningful share of its full-load power, which keeps the DG busier than you might expect.

Condenser fans and pumps

Evaporative or air-cooled condensers need fans, and evaporative units need water pumps too. Their load rises in summer because the system works harder to reject heat when ambient temperature climbs.

Evaporator fans

Each chamber has air coolers with fans that run almost continuously to circulate cold air across the stack. Individually small, together they form a steady base load that runs round the clock.

Defrost heaters

Chambers held below freezing, or high-humidity rooms where coils frost up, use electric defrost heaters, hot gas defrost or water defrost. Electric defrost adds a sharp, short-lived block of resistive load, often tens of kilowatts per chamber, for 20 to 40 minutes at a time.

Ripening rooms

Multi-commodity stores that ripen bananas or mangoes run ripening chambers with ethylene dosing, heating for pulp temperature control, and then cooling to remove the heat released by ripening fruit. These rooms have their own cycle, separate from the long-term holding chambers.

Lighting, docks and office

Lighting, dock levellers, rapid-roll doors, forklift chargers and the office are small loads, but dock activity peaks during fresh loading, exactly when refrigeration demand is highest.

For broader guidance on summing connected loads, see load calculation basics before buying a generator. For cold store design standards and benchmarks, the National Centre for Cold-chain Development publishes NCCD basic data sheets, a useful technical reference for refrigeration specifications in Indian conditions.

The Five Cold Store Load Patterns

Most cold stores cycle through five recognisable patterns over a year. Each has a different meaning for exhaust temperature and filter health.

Load pattern	When it happens	Typical DG load share (illustrative)	What it means for the DPF
Pull-down after fresh loading	Days after a chamber is filled with warm produce	High, often 65 to 85%	Good passive regeneration; filter cleans itself
Holding or steady state	Weeks or months after pull-down	Low to moderate, often 20 to 40%	Risk of soot build-up if this is most running time
Defrost spikes	Several times a day in frozen or humid chambers	Short bursts above holding load	Too brief to regenerate on their own
Seasonal peaks	Loading season and summer afternoons	Moderate to high	Helpful regeneration windows
Night tariff, DG-only and rural grid sites	Off-peak hours, weak grids, unconnected sites	Varies widely; often light at night	Long light-load hours are the main risk

1. Pull-down after fresh loading

When warm produce enters a chamber, the refrigeration plant must remove field heat and bring the product down to storage temperature. Compressors run at or near full capacity for days. If the DG carries the plant during this period, it runs well loaded and the exhaust is hot. This is the friendliest period for a DPF.

2. Holding or steady state

Once product reaches set point, the plant only needs to cover heat leaking through walls, doors, fans, lights and respiration of the stored produce. Compressors unload or cycle. The DG load can fall to a quarter or a third of rating. In a store that holds potatoes for seven or eight months, holding is where the DG spends most of its life.

3. Defrost spikes

Electric defrost adds a resistive block of load for a short period, while the compressor serving that chamber may pause. The net effect is a short spike. These spikes help a little, but 30 minutes of higher load every six hours will not keep a filter clean if the remaining hours are light.

4. Seasonal peaks

Two seasonal peaks matter in North India.

• Loading season. Many multi-commodity and potato stores in Uttar Pradesh, Punjab and West Bengal fill rapidly during February and March when potatoes are harvested. Several chambers go into pull-down in quick succession, and the plant runs hard for weeks.
• Summer ambient peak. From April to June, outdoor temperatures push condensing pressure up. Compressors draw more power for the same cooling, and condenser fans and pumps work harder. Even a store in holding mode can see its afternoon load rise noticeably.

Both peaks are good for regeneration. The challenge comes in the cooler months when the store is in holding mode and ambient temperatures are low.

5. Night tariff, DG-only sites and rural grids

Some stores shift heavy refrigeration to night hours when tariffs are lower, using the thermal mass of the product as a buffer. Others sit on rural feeders with long scheduled outages, or have no reliable grid at all and run largely on DG. In these cases the DG can run for many hours at night carrying only holding load, which is the classic light-load scenario. A DG-only site is also a case where the generator is effectively prime power rather than standby, so its running hours and duty cycle look very different from a typical backup set.

Compressor Starting and Its Effect on DG Sizing

The single biggest reason cold store DGs run light is that they were sized for compressor starting, not for running load.

When an induction motor starts direct on line (DOL), it can draw several times its full-load current for a few seconds. The DG must supply that inrush in kVA without excessive voltage dip, or contactors chatter, other motors stall and the controller may trip. Sizing to survive the largest motor start often leads to a generator much larger than the steady load needs. Our explainer on how to read a generator’s kVA and kW rating helps with the kVA versus kW distinction here.

Starting method	Relative starting kVA (illustrative)	Effect on DG sizing
Direct on line (DOL)	Highest, often 5 to 7 times running kVA	Forces the largest DG; light running afterwards
Star-delta	Roughly one third of DOL	Moderate reduction; transition spike still present
Soft starter	Adjustable, typically 2 to 4 times running kVA	Smaller DG possible; smoother voltage
Variable frequency drive (VFD)	Close to running current	Smallest DG for the same plant; watch harmonics

The practical point for RECD planning: if your DG was sized around a DOL start of a large compressor, it may spend most of its running hours at 25 to 35% load. Changing starting methods (for instance, fitting soft starters, or moving a screw compressor to VFD) and sequencing compressor starts so that only one machine starts at a time can open the door to a smaller DG later. For the general method, see generator sizing for factories. VFDs introduce harmonic currents, so confirm with your DG maker and electrical consultant that the alternator and AVR can handle them.

How to Log Your Cold Store’s Load

Before choosing an RECD, log the actual load your DG carries across a representative period.

What to log

• Real power (kW), apparent power (kVA) and power factor at the DG output terminals, at one-minute or shorter intervals.
• Current per phase, to spot imbalance.
• Run hours, start and stop times, and the reason for each run (grid failure, scheduled test, tariff decision).
• Exhaust temperature, if you can install a probe at a suitable point on the exhaust pipe, ideally where the RECD would sit.
• Chamber status for the same period: which chambers were in pull-down, holding or defrost.

How long to log

Aim for 7 to 14 days at minimum. One week captures daily and defrost cycles. Two weeks gives more confidence, especially if it includes a grid outage pattern typical of your feeder. If you can, repeat the exercise in a second season, for instance once during loading and once during winter holding.

Tools you can use

1. Clamp meter or portable power analyser on the DG output. A logging power analyser is best because it records kW and kVA continuously.
2. DG controller history. Many modern controllers store load, run hours and alarms. Download whatever history is available.
3. Run-hour logbook. Your operators’ manual log is valuable, especially if it notes why the DG was started.
4. Exhaust temperature probe. A thermocouple with a logger gives the most direct evidence of whether regeneration conditions exist.

For the theory behind interpreting these numbers, read understanding generator load factor and duty cycle.

Illustrative Worked Example: A 5,000 Tonne Multi-Chamber Store

The following is an illustrative composite, not a real customer. Numbers are rounded for clarity.

A 5,000 tonne multi-commodity cold store in western Uttar Pradesh has eight chambers, two of them able to run below freezing, and two banana ripening rooms. Refrigeration uses four reciprocating ammonia compressors with star-delta starters and one screw compressor with a soft starter. Backup is a single 500 kVA DG set, which at 0.8 power factor gives a nominal 400 kW. The DG was sized years ago around compressor starts plus a margin for expansion.

The manager logs DG output for 14 days in two separate periods: once in March during loading, and once in December during holding.

Phase (illustrative)	Typical running kW	Approx. % of 400 kW	DG hours in log period	Comment
March, pull-down of 3 chambers	290 to 330	72 to 82%	38	Strong regeneration window
March, holding plus 1 chamber loading	200 to 240	50 to 60%	46	Generally adequate
December day, holding	120 to 150	30 to 38%	52	Borderline
December night, holding	85 to 110	21 to 28%	64	Light load; soot will accumulate
Defrost spikes (any season)	Holding plus 30 to 45	Brief bursts	Under 1 hour per day	Not enough on its own

What this tells the manager

During loading season, the DG is in a comfortable range and a passive DPF would regenerate well. In December, more than half of the DG hours fall at or below 30% load, mostly at night. Left unaddressed, those hours would load the filter with soot and push backpressure upward.

The manager now has real options rather than guesses:

• Shift some holding-mode compressor duty to concentrate load on fewer machines running harder, rather than many machines lightly loaded.
• Schedule a planned high-load run or a load bank exercise at intervals during winter.
• Ask the RECD vendor whether an active regeneration feature or a different filter specification suits this duty.
• Consider whether a smaller second DG, or a dual fuel conversion, fits the winter profile better.

The 500 kVA DG set RECD page gives an idea of what the device for this size of set involves, but the load log should drive the conversation with the vendor.

Decision Table: What Your Load Log Tells You

Use this as a starting framework, then confirm specifics with the RECD vendor and your DG maker.

What the log shows	Interpretation	Suggested next step
Most running hours consistently above 50% load	Good passive regeneration conditions	Proceed with a standard RECD specification; normal monitoring
Mixed: 40 to 50% load for most hours, some lighter periods	Regeneration likely adequate with care	Proceed, but set backpressure alarms and review data monthly
Long periods below 30% load, especially in winter or at night	High risk of soot loading	Consider load management, staged compressor scheduling, periodic load bank exercise, or active regeneration options
DG mostly runs only for short tests, rarely for outages	Very low duty	Discuss low-duty strategies with vendor; read our guide on occasional-use DG sets
DG grossly oversized because of DOL compressor starts	Structural light running	Explore soft starters or VFDs and right-sizing; evaluate a dual fuel route if eligible
Large swings between seasons	Seasonal variation	Plan maintenance and exercise runs around the lighter months

If your DG runs only occasionally, our post on whether an RECD suits a DG set that runs only occasionally addresses that profile in more depth.

On the regulatory side, CAQM Direction No. 76 for the NCR placed DG sets in the 125 to 800 kW band on a choice between dual fuel and an RECD, while sets in the 19 to 125 kW band were directed toward dual fuel and sets above 800 kW toward an RECD. You can read the CAQM Direction 76 document directly. Check the current CAQM direction and your State Pollution Control Board, since rules and GRAP stage restrictions can change. If your set falls in the band with a choice, the load log helps decide between the two. Compare both routes in our RECD vs dual fuel kit guide, and see the dual fuel kit page for how the gas route works.

Scheduling the Retrofit Around the Storage Cycle

Fitting an RECD typically means a day or two of DG downtime per set for fitment, though this varies by site. For a cold store, the timing of that downtime is as important as the device itself. Product worth crores depends on the refrigeration running.

Choose the right window

• Best: when chambers are near empty, between seasons, or when the store is in stable holding with low outage risk.
• Acceptable: during holding, if grid supply is reliable and backup power is arranged.
• Never: during pull-down after fresh loading. Losing refrigeration then means warm produce sits without cooling, which risks quality, weight loss and spoilage.

Know your temperature buffer

Every chamber has a buffer, the number of hours it can hold product within acceptable limits with doors shut and refrigeration off. A well-insulated, fully stacked frozen chamber may hold for a long time. A half-full chamber of fruit in summer may not. Estimate this buffer with your refrigeration engineer before booking the retrofit.

Keep backup in place

Arrange a rental DG of suitable rating to stand in while your own set is out of service, or confirm that the grid is reliable enough to accept the risk. If you use a rental set, plan the temporary cable route, changeover arrangements and fuel in advance.

Talk to your insurer

Check whether your stock insurance covers spoilage during planned work on backup equipment. A short email to your broker is cheap protection.

Hot work precautions

Cutting or welding the exhaust pipe needs a hot work permit, a fire watch, and extinguishers at hand. Cold stores often have large volumes of insulation panels and packaging nearby, so treat this seriously. Our RECD installation timeline guide sets out the stages from survey to commissioning.

Food business operators should also keep in mind hygiene obligations under the FSSAI Schedule 4 general hygienic and sanitary practices, particularly around maintaining temperature control and avoiding contamination from construction work near storage areas.

Post-Retrofit Monitoring

Once the RECD is fitted, the load log you built becomes a baseline. Keep watching.

Backpressure

Backpressure is the clearest sign of filter health. Track it alongside DG load. A gradual rise during the winter holding season, followed by a fall during summer or loading, shows passive regeneration is working across the year. A steady climb that does not recover tells you the filter is loading faster than it cleans.

Exhaust temperature trends

Pair exhaust temperature with load. If temperatures sit consistently below the regeneration range for long periods, act before backpressure reaches alarm level.

Use IoT monitoring

Modern RECDs, including those from Aceget, offer a touch display and IoT monitoring with remote access. For a cold store manager, this means backpressure and temperature trends can be checked from a phone, and alerts can be sent before a problem becomes an outage. Set alarm thresholds in consultation with the vendor, within the engine maker’s backpressure limit.

Maintenance routine

Fold RECD checks into your existing DG routine, and repeat the load logging exercise each year as chambers and compressors change. Our RECD maintenance guide covers this in more detail.

Frequently Asked Questions

Will an RECD work on a cold store DG that mostly runs at light load?

It can, but it needs planning. Long light-load running slows passive regeneration and allows soot to build up. Options include load management, staged compressor scheduling, periodic load bank runs, and discussing active regeneration features with the vendor. Your load log tells you which of these you need.

Does compressor starting current matter for the RECD itself?

Not directly, since starting current affects alternator sizing, not the exhaust. Indirectly it matters a lot: a DG sized for DOL starts usually runs lightly loaded, which slows regeneration.

How long should I log load before deciding?

Seven to 14 days is a sensible minimum. Logging during both loading season and winter holding gives the clearest picture, because those are the extremes of a typical cold store year.

When is the best time to fit an RECD at a cold store?

When chambers are near empty or in a stable holding phase, with backup power arranged. Avoid pull-down periods entirely. Check your temperature buffer hours and insurance before scheduling.

Does fitting an RECD reduce the power my DG can deliver?

A correctly specified RECD should keep backpressure within the engine maker’s limit, so rated output should not be meaningfully affected. Problems arise when the filter is allowed to load up with soot, which is why monitoring matters.

Should a cold store choose an RECD or a dual fuel kit?

It depends on the DG’s power band under the current CAQM direction, gas availability at your site, and your load profile. A DG that spends long hours at light load may suit one route better than the other. Compare both with your vendor using real load data.

Plan Your Cold Store Retrofit With Real Data

A cold store’s DG works through a year of pull-down, holding, defrost and seasonal peaks, and the RECD has to cope with all of them. Logging your load first turns a generic purchase into a specified, monitored installation that suits your refrigeration cycle. Aceget designs and supplies CPCB type-approved RECDs for DG sets from 25 kVA to 2500 kVA, with IoT monitoring for ongoing visibility. To share your load log and nameplate details, contact the Aceget team or review the retrofit emission control device range.