Cold Thermal Energy Storage | Ice Storage, Chilled Water, PCM & Cryogenic Cold

Cold Energy Storage

Make the cold at night, use it in the afternoon.

Cooling is one of the largest and fastest-growing electricity loads in India, and it peaks in the hot afternoons and evenings when the grid is most stressed. Cold storage makes ice or chilled water when power is cheap or solar is plentiful, and releases the cooling during the peak. It cuts peak demand charges, lets chillers be smaller and gives critical sites a cooling reserve. BARREL can study, design, build and operate cold storage for buildings, campuses, district cooling, data centres, cold chain and industry, with equipment through OEM partners.

Sector hub · 24 sections

Section 01

Cold Storage — Overview

Cold thermal energy storage keeps cooling capacity in water, ice, a phase-change material or a cryogenic liquid. Chillers run when power is cheap or solar is plentiful; the store supplies the building or process later.

It is not a battery: it stores cooling, not electricity. But because cooling is often the largest electric load on a site — 40–60 % of the bill in many Indian offices, malls and hospitals — shifting it has much the same effect on the bill and on the grid, usually at a lower cost per kWh shifted than batteries.

1.1Cold storage media at a glance

Cold storage media at a glance
Medium	How it stores cold	Store size for the same cooling	Best for
Chilled water	Sensible heat, water stored at about 4–6 °C in a stratified tank	Largest (≈ 8–12 kWh(th)/m³)	Campuses, district cooling, data centres, large industry
Ice	Latent heat of freezing at 0 °C	About ⅕ to ⅓ of chilled water	Buildings with limited space, low-temperature supply
Phase-change materials	Latent heat at a chosen temperature (−30 °C to +20 °C)	Small	Cold chain, cold rooms, retrofit, special temperatures
Cryogenic	Liquid air, nitrogen or LNG at −160 to −196 °C	Small, but very cold	LNG terminals, industry, liquid air energy storage

1.2Why sites install cold storage

Lower bills

Run chillers on night or solar-hour tariffs and avoid the peak tariff and the maximum-demand charge.

Smaller chillers

In a new building the chiller plant can be sized for the average load, not the peak, saving capital.

Grid support

Shifts several MW of afternoon and evening load into the solar hours or the night, helping the DISCOM.

Cooling reserve

Hospitals and data centres keep minutes to hours of cooling if chillers or power fail.

Solar matching

Store midday solar as cold for the evening, raising rooftop and open-access solar use.

Longer life

Chillers run steadily at their best load instead of cycling; tanks last 25–30 years.

Ice-on-coil
Encapsulated ice
Ice slurry
Stratified chilled water
Low-temperature fluid
PCM
LNG cold
Liquid air
District cooling
Data centres
Cold chain

Ice stores about 334 kJ/kg as latent heat — roughly 85 kWh of cooling per cubic metre of solid ice, or about 40–50 kWh per cubic metre of practical tank. Chilled water at an 8 K temperature difference holds about 9 kWh per cubic metre. All figures on this page are typical or indicative ranges from public literature, not project guarantees.

Section 02

How Cold Storage Works

Every cooling system moves heat out of a building or process and rejects it outside. A cold store simply puts a reservoir between the chiller and the load: the chiller fills the reservoir with cold when it suits the tariff, and the load draws from it when it needs cooling.

Cold can be stored as sensible heat (water gets colder, then warmer) or as latent heat (water freezes into ice, then melts). Latent storage packs far more cooling into the same volume, but the chiller has to work at a lower temperature to make it.

2.1Daily charge and discharge cycle

Off-peak or solar hours
Chiller runs at full, efficient load
Store charges (water cools or ice forms)
Peak hours
Store discharges
Chilled water to AHUs or process
Chillers off or throttled
Peak demand and bill cut

2.2Sensible versus latent storage

Sensible versus latent storage
Aspect	Sensible (chilled water)	Latent (ice / PCM)
What changes	Temperature of the water	State: liquid ↔ solid at a fixed temperature
Energy per kg	4.19 kJ/kg per kelvin (≈ 33 kJ/kg at ΔT 8 K)	334 kJ/kg for ice; 150–250 kJ/kg for most PCMs
Chiller leaving temperature	4–6 °C (normal chiller)	−6 to −3 °C glycol for ice; matched to PCM melting point
Chiller efficiency while charging	Normal	Lower: capacity and COP fall by roughly 20–35 % for ice-making
Supply temperature on discharge	Same as charge, 4–6 °C	As low as 1–3 °C from ice — allows low-temperature air
Tank size	Large	Small

2.3Key terms in plain words

Ton of refrigeration (TR)

1 TR = 12,000 Btu/h
1 TR = 3.517 kW of cooling
Indian HVAC uses TR everywhere

TR·h (ton-hour)

1 TR for one hour
1 TR·h = 3.517 kWh(th)
Storage size is quoted in TR·h

ΔT (delta-T)

Return minus supply water temperature
Typical 5.5 K (old), 8–10 K (good design)
Wider ΔT = smaller tank and pumps

COP / kW per TR

COP = cooling ÷ electricity
Good water-cooled plant 0.6–0.8 kW/TR (chiller only)
Whole plant incl. pumps and towers 0.8–1.2 kW/TR

Full / partial storage

Full: chillers off at peak
Partial: chillers and store share the peak
Choice set by tariff and space

Thermocline

The thin layer between cold and warm water
Typically 0.3–1 m thick
Kept sharp by slow, even flow

kW per TR and COP figures are indicative for Indian conditions (35–45 °C ambient); actual values depend on the chiller, condenser water temperature and part load.

Section 03

Ice-on-Coil Storage

The most common ice storage in buildings. Plastic or steel coils sit in a tank of water. During charging a glycol solution at about −6 to −3 °C flows through the coils and ice builds up on the outside of the tubes. During discharge the ice melts and chills the building's water loop.

Two variants exist. In internal melt, warm glycol flows back through the same coils and melts the ice from the inside — the tank water never leaves the tank. In external melt, the building's water circulates directly over the ice, giving very cold water and fast discharge.

3.1Internal melt versus external melt

Internal melt versus external melt
Feature	Internal melt	External melt
Fluid in contact with ice	Glycol inside the coil	System water over the ice
Typical supply temperature	1–4 °C (glycol)	About 1–2 °C (water)
Discharge rate	Moderate, falls as ice melts	High, steady
Tank	Closed, modular, factory-built	Open, often site-built concrete
Ice build-up control	Simple; coil fully frozen	Thickness must be limited to keep water paths open
Typical use	Offices, malls, hospitals, hotels	District cooling, process, large plants
Water treatment	Tank water static	Tank water in circuit; treatment needed

3.2What the system contains

Ice tanks

Modular polyethylene or steel tanks
Or large concrete pits with coil bundles
Insulated lid and walls

Glycol loop

25–30 % ethylene or propylene glycol
Glycol chillers rated for ice duty
Plate heat exchanger to the water loop

Controls

Ice inventory sensor (level or conductivity)
Charge / discharge valves
Mode logic in the BMS

3.3Operating modes

Ice-making (night)
Ice-making plus direct cooling (night loads)
Chiller only (mild days)
Ice melt only (peak, chiller off)
Chiller plus ice melt (design day)

Temperatures and glycol concentrations are typical values; the OEM's selection software sets the exact figures for each tank and load profile.

Section 04

Encapsulated Ice and Dynamic Ice Systems

Encapsulated systems fill thousands of plastic balls or flat containers with water (or a PCM), pack them into a steel or concrete tank and pass cold glycol around them. The water inside freezes; on discharge warmer glycol melts it. The tank can be any shape, so it fits basements and odd spaces.

Dynamic systems make ice and move it: ice harvesters freeze thin sheets on plates and drop them into a pit; ice-slurry machines make a pumpable mixture of tiny crystals in water. Both charge and discharge very fast.

4.1Types

Static

Ice balls (nodules)

Plastic spheres, typically 75–100 mm, filled with water and a nucleating agent. Packed tank holds about 50–60 % water by volume. Simple, no moving parts.

Static

Flat containers and plates

Rectangular capsules stacked in racks; good flow distribution and easy inspection. Also used with PCMs at +5 to +10 °C.

Dynamic

Ice harvester

Water flows over refrigerated plates; a thin ice sheet forms and is released by a brief hot-gas defrost into a storage pit. Water at about 1 °C is drawn off.

Dynamic

Ice slurry

A scraped-surface or supercooling generator makes fine crystals; the slurry is pumped to storage or straight to the load. Very fast discharge.

Static

Ice-on-pipe in pits

Large site-built pits with bare-pipe coils, used in district cooling and dairies (the classic Indian ice bank).

Industry

Ice banks for dairies

Milk chillers have used ice banks for decades so small compressors can cool milk quickly at collection times.

4.2Choosing between ice systems

Choosing between ice systems
System	Space needed	Discharge speed	Efficiency while charging	Complexity
Ice-on-coil, internal melt	Low	Medium	Medium	Low
Ice-on-coil, external melt	Low	High	Medium–low (thicker ice)	Medium
Encapsulated	Low–medium	Medium	Medium	Low
Ice harvester	Medium	Very high	Lower (defrost cycles)	High
Ice slurry	Medium	Very high	Medium	High

Ball sizes, packing fractions and comparative ratings are indicative; they vary by product and should be confirmed from OEM data for each design.

Section 05

Stratified Chilled-Water Storage

A large insulated tank holds cold water (about 4–6 °C) at the bottom and warm return water (about 12–16 °C) at the top. Because cold water is denser, the two layers stay apart with a thin thermocline between them. Slow, even diffusers at top and bottom keep the layers from mixing as water is drawn and returned.

Chilled-water tanks are the cheapest cold store per kWh at large scale, use normal chillers at normal efficiency, and can double as a fire-water reserve. Their drawback is size — for the same cooling they need roughly three to five times the volume of an ice store.

5.1How much cooling a tank holds

Stored cooling

Q = V × ρ × cₚ × ΔT × FoM ÷ 3,600

5,000 m³ × 1.163 kWh/m³·K × 8 K × 0.9 ≈ 41.9 MWh(th) ≈ 11,900 TR·h

A wider temperature difference between supply and return stores more cooling in the same tank. The figure of merit allows for the thermocline and mixing that make part of the water unusable.

Symbol	Meaning
V	Water volume (m³)
ρ × cₚ	≈ 4,186 kJ/m³·K for water (= 1.163 kWh/m³·K)
ΔT	Return minus supply temperature (K)
FoM	Figure of merit, typically 0.85–0.95 for a well-designed tank
Q	Stored cooling (kWh thermal)

5.2Design points that make a tank work

Geometry

Tall tanks stratify better; height 10–30 m is common
Height-to-diameter ratio often 0.5–1.5 for large tanks
Above ground (steel or concrete) or partly buried

Diffusers

Octagonal or radial pipe diffusers, or slotted plates
Low inlet velocity so cold water spreads as a gravity current
Design on inlet Froude number (≈ 1 or below) and Reynolds number

Temperatures

Supply 4–6 °C; water is densest near 4 °C
Return as warm as the coils allow (12–16 °C)
Low-temperature fluid additives allow supply near 1–2 °C

Extras

Tank can serve as fire-water storage (with approval)
Also usable as a hot-water store in winter climates
Sensors every 0.3–1 m up the tank wall to track the thermocline

Large insulated cylindrical storage tanks at an energy plant — Reference: large insulated above-ground storage tanks (here, molten-salt tanks at a solar thermal plant). Chilled-water storage tanks look much the same from outside.

Temperatures, figure-of-merit values and tank proportions are typical ranges from ASHRAE guidance and published case studies; each tank needs its own diffuser and stratification design.

Section 06

Phase-Change Materials (PCM) for Cold Storage

A phase-change material melts and freezes at a chosen temperature, so cold can be held exactly where a product or process needs it — +8 °C for chilled water, +2 to +8 °C for vaccines, −18 to −25 °C for frozen food.

PCMs are packed in capsules, panels, plates or containers. They charge from a chiller, a refrigeration unit or solar-powered compressors, and hold temperature through power cuts — a strong advantage in rural Indian cold chains.

6.1PCM families

PCM families
Family	Typical melting range	Latent heat (indicative)	Notes
Water / ice	0 °C	334 kJ/kg	Cheapest, best known
Eutectic salt solutions	−50 to 0 °C	150–300 kJ/kg	Frozen food, ice-cream, reefer plates; can be corrosive
Salt hydrates	+5 to +30 °C	150–250 kJ/kg	High density; need stabilisers against separation
Paraffins	−10 to +30 °C	150–250 kJ/kg	Stable, non-corrosive; flammable, lower density
Bio-based (fatty acids, esters)	−20 to +30 °C	150–200 kJ/kg	Renewable feedstock; cost falling

6.2Where PCMs are used

Cold rooms and pack houses

PCM panels in the walls or ceiling hold temperature through 6–12 h of power cuts; solar compressors charge them by day.

Vaccine and pharma

PCM packs in shippers and refrigerators keep +2 to +8 °C without power for days.

Reefer trucks and containers

Eutectic plates charged at the depot replace diesel-driven refrigeration on short routes.

Chilled-water plants

Encapsulated PCM at +5 to +10 °C works with normal chillers and stores more per m³ than water.

Data-centre racks

Small PCM buffers at rack or row level ride through short cooling outages.

Milk chilling

PCM or ice-bank chillers at village collection centres cool milk without a reliable grid.

6.3Points to check

Supercooling: some PCMs freeze below their melting point; nucleating agents are needed.
Phase separation in salt hydrates over many cycles.
Low thermal conductivity: fins, thin plates or capsules are needed for fast charging.
Flammability (paraffins) and corrosion (salts) — container material and fire rules.
Cycle-life test data from the supplier (thousands of cycles).
End-of-life take-back and disposal.

Melting ranges and latent heats are indicative ranges from published PCM literature; each product has its own data sheet.

Section 07

Cryogenic Cold — LNG Cold Recovery and Liquid Air

LNG arrives at import terminals at about −162 °C and must be warmed back to gas, normally by sea water or burners. That warming throws away a large amount of high-grade cold. Recovering it can run air-separation units, cold warehouses, data-centre cooling or even a small power cycle.

Liquid air (about −194 °C) and liquid nitrogen (−196 °C) can also be used as stores: liquid air energy storage makes liquid air with surplus power and later re-gasifies it to drive a turbine, reusing the stored cold to cut the next liquefaction's energy.

7.1Uses of cryogenic cold

LNG terminal cold

Air separation (oxygen, nitrogen)
Cold warehouses and food freezing next to the terminal
Power from a cold Rankine cycle
Cooling for nearby data centres or industry

Liquid air / nitrogen

Liquid air energy storage (power-to-power)
Cryogenic freezing of food and medicine
Back-up cooling for critical sites
Truck refrigeration with liquid nitrogen

Hydrogen and future fuels

Liquid hydrogen at −253 °C
Boil-off and cold recovery at LH₂ terminals
Cold reuse in hydrogen liquefiers

7.2Reference facts (indicative)

Reference facts (indicative)
Item	Value / fact
LNG temperature	About −162 °C at near-atmospheric pressure
Cold released warming LNG to ambient	About 800–900 kJ/kg (latent plus sensible); only a part is usefully recoverable
Liquid nitrogen boiling point	−196 °C
Liquid air energy storage round-trip	Roughly 50–70 % in studies, higher with waste heat or waste cold
Reference plant	A 5 MW / 15 MWh pre-commercial liquid air plant ran near Manchester, UK, from 2018
LNG cold power	Japanese LNG receiving terminals have used LNG cold for power generation and air separation since the late 1970s
India LNG terminals	West coast: Dahej, Hazira, Dabhol, Kochi, Mundra; east coast: Ennore, Dhamra

A large spherical insulated cryogenic storage tank — Reference: a spherical cryogenic storage tank of the kind used for liquefied gases.

Cryogenic cold projects are site-specific and need PESO approvals for pressure vessels and gas handling. Efficiency and energy figures are indicative from public studies.

Section 08

System Types and Configurations

How much of the peak the store carries, and where it sits in the pipework relative to the chiller, decides tank size, chiller size and savings. The choice follows from the 24-hour load profile, the tariff and the space available.

8.1Operating strategies

Operating strategies
Strategy	What it means	Tank	Chiller	Best when
Full storage	Chillers off during the peak; the store carries all cooling	Largest	Sized to recharge in off-peak hours	Peak tariff is very high or demand charge dominates
Partial storage — load levelling	Chillers run all day at a steady rate; the store tops up the peak	Moderate	Smallest (≈ daily TR·h ÷ 24)	New building; capital saving on chillers matters
Partial storage — demand limiting	Chillers capped at a set kW during the peak	Moderate	Between the two	A target maximum demand or contract demand
Back-up / ride-through	Store kept full; used only when chillers or power fail	Small	Normal	Data centres, hospitals, pharma
Solar-matched	Charge during solar hours, discharge evening and night	Moderate	Sized for solar window	Large rooftop or open-access solar, ToD solar-hour tariff

8.2Piping arrangements

Chiller upstream (series)

Chiller cools first, ice trims
Chiller runs at warmer, more efficient temperature
Common with ice-on-coil

Chiller downstream (series)

Ice cools first, chiller trims
Uses ice fully; chiller at lower temperature
Good for low-temperature supply

Parallel

Chiller and store each feed the load
Typical for chilled-water tanks
Tank acts as the decoupler

8.3By scale

Small

Cold rooms, shops, telecom: PCM or modular ice, 50–1,000 TR·h.

Building

Office, mall, hospital, hotel: ice-on-coil or encapsulated, 1,000–20,000 TR·h.

Campus / industry

Universities, pharma, auto plants: chilled-water tank, 10,000–60,000 TR·h.

District

Business districts, smart cities, airports: chilled-water or external-melt ice, 50,000 TR·h and above.

Size bands are indicative and overlap; the right medium is chosen by cost, space and supply temperature, not by scale alone.

Section 09

Technical Architecture and Components

A cold-storage plant is a chiller plant with an extra reservoir and a smarter control strategy. Most components are standard HVAC equipment made in India; the storage tank, diffusers or ice coils and the controls are where the design skill lies.

9.1Main components

Cooling production

Water-cooled screw or centrifugal chillers
Glycol / ice-duty chillers (dual-duty)
Air-cooled chillers for small sites
Cooling towers and condenser pumps

Storage

Steel or concrete tank, or modular ice tanks
Diffusers, ice coils or capsules
Insulation and vapour barrier
Level, temperature and inventory sensors

Distribution

Primary and secondary pumps with VFDs
Plate heat exchangers (glycol to water)
Motorised mode valves
Air separators, expansion tanks, strainers

Loads

Air-handling units and fan-coil units
Process heat exchangers
Data-hall CRAH units
Cold rooms and blast freezers

Water and glycol

Chemical dosing and side-stream filters
Glycol make-up and test kits
Make-up water and softening

Controls

Plant controller or BMS
Energy meters (BTU meters) and power meters
Tariff and weather inputs
SCADA for district systems

9.2Energy path

Grid or solar power
Chiller compressors
Glycol or chilled water
Storage tank
Heat exchanger / pumps
AHUs, process, data halls
Heat back to chiller
Cooling tower to atmosphere

9.3Typical design life

Typical design life
Component	Typical life (indicative)
Concrete or steel tank	25–40 years
Ice coils and capsules	20–30 years
Chillers	20–25 years
Pumps and motors	15–20 years
Controls hardware	10–15 years (software updated throughout)

Section 10

Electrical, Controls, Monitoring and Digital

The controls decide whether a cold store saves money. A good controller knows the tariff, the weather forecast and the building's load pattern, charges the store just enough, and discharges it so it is empty exactly when the peak ends.

Electrically, cold storage needs no inverters or batteries. It changes when the chiller motors run, so the main electrical work is the chiller and pump feeders, VFDs, power-quality checks and metering for demand charges.

10.1Control layers

Field

Tank temperature string
Ice inventory sensor
Flow and BTU meters
Valve and pump status

Plant controller / BMS

Mode selection (charge, discharge, chiller only, both)
Chiller sequencing and set-points
Discharge-rate limits
Alarms and interlocks

Supervisory / EMS

Tariff calendar (ToD, solar hours)
Weather-forecast load prediction
Demand-limit targets
Demand-response signals from the DISCOM

10.2Digital and AI tools

Load forecasting

Machine-learning models predict next-day cooling load from weather, occupancy and calendar data.

Optimal dispatch

Model-predictive control chooses the cheapest hour-by-hour plan for chillers and store.

Digital twin

A plant model checks savings, tests control changes before going live and flags drift.

Fault detection

Detects fouled coils, poor stratification, glycol loss or stuck valves from trend data.

Measurement and verification

Baseline versus actual demand and energy, following IPMVP-style methods.

Remote monitoring

Dashboards for kW/TR, TR·h stored, peak shaved and savings, with mobile alerts.

10.3Electrical scope

LT panels and feeders for chillers, pumps and cooling towers
VFDs on pumps and tower fans; harmonic check to IEEE 519
Maximum-demand monitoring and contract-demand review with the DISCOM
Power and BTU metering for savings verification
DG and UPS planning for critical-cooling sites
Earthing, lightning protection and cable sizing to Indian codes

Operators at screens in a plant control room — Reference: a plant control room. District cooling and large campus plants are run from similar SCADA desks.

Section 11

Applications and Site Integration

Any site where cooling is a large share of the power bill, or where cooling must never stop, is a candidate. The store is integrated into the existing chilled-water system with a few valves and pumps, or designed into a new plant from the start.

11.1Where cold storage fits

Malls, airports, hospitals, hotels

Shift the afternoon peak, downsize chillers in new buildings, and use cheaper night or solar-hour power.

District cooling

One central plant and tank serves a business district, smart city, airport or campus through insulated pipes.

Data centres

Chilled-water tanks give 5–15 minutes (or more) of cooling while chillers restart after a power event.

Cold chain

Pack houses, ripening chambers, cold rooms and warehouses for fruit, vegetables, dairy, vaccines and pharma.

Process industry

Dairy, beverages, pharma, chemicals, plastics and auto plants with large chilled-water loads.

Solar-driven cooling

Store midday solar as ice or chilled water for the evening; cuts export or curtailment.

11.2Data centres and district cooling in more depth

Data centres

Cooling is 25–40 % of facility power in older Indian sites
Tank sized for chiller restart time plus margin
Pumps on UPS so chilled water keeps flowing
Works with ASHRAE TC 9.9 allowable inlet ranges
Also used to shift load in large hyperscale campuses

District cooling

Large chilled-water tanks of 10,000–100,000 m³ in the Gulf, Singapore and US campuses
Tank lets the plant run at steady, efficient load
Wide ΔT (8–10 K) cuts pipe sizes
Tariff per TR·h and connection charge to buildings
India: GIFT City (Gujarat) runs India's first large district cooling network

Rows of server racks in a data hall — Reference: a data hall. Chilled-water storage keeps such halls cool while chillers restart after a power interruption.

11.3Integrating with an existing chiller plant

1Log 2–4 weeks of hourly chiller load, kW and temperatures
2Check spare space (basement, roof, ground) and structural capacity
3Choose tie-in points and confirm existing chiller can make ice or needs a new glycol chiller
4Add tank, pumps, heat exchanger and mode valves with minimal shutdown
5Upgrade BMS sequences and add tariff logic
6Commission in stages and verify the peak cut against the baseline

Data-centre and district-cooling figures are typical published ranges; each site's ride-through time and tank size come from its own risk and load study.

Section 12

Civil and Mechanical Works

The tank is the largest structure in a cold-storage project. A chilled-water tank can weigh tens of thousands of tonnes when full, so foundations, seismic design, insulation and waterproofing need the same care as a water-supply reservoir.

12.1Tank construction options

Tank construction options
Option	Typical size	Advantages	Watch-outs
Welded steel, above ground	1,000–50,000 m³+	Fast to build, tall (good stratification)	External insulation and cladding; corrosion protection
Prestressed concrete (wire-wound)	5,000–100,000 m³	Long life, low maintenance, can be partly buried	Specialist contractor; longer build
Reinforced concrete pit / basement	100–10,000 m³	Uses space under buildings or car parks	Waterproofing, internal insulation, access
Modular factory ice tanks	50–500 TR·h each	Quick install, roof or basement	Floor loading; many connections
Bolted / panel tanks	50–2,000 m³	Low cost for small sites	Lower height, weaker stratification

12.2Civil and mechanical design checks

Structure

Soil investigation and foundation design
Hydrostatic, wind and seismic loads (IS 1893, IS 875)
Liquid-retaining concrete to IS 3370
Steel tank design to API 650 / AWWA D100 or IS 803

Thermal

Insulation thickness for < 1–2 % daily heat gain
Closed-cell foam or PIR with vapour barrier
Bottom insulation against ground heat
Cladding against Indian sun and monsoon

Mechanical

Diffuser fabrication and levelling
Pipe supports, expansion and anchors
Nozzle and manway design
Overflow, vent and drain

12.3Site works

Crane access and laydown area for tank plates or ice modules
Hydrotest water source and discharge route
Drainage and bunding around the tank
Underground pipe routes with insulation and sleeving
Lightning protection and earthing of steel tanks
Architectural treatment where the tank is visible

Tank sizes and heat-gain targets are indicative. Codes listed are the usual references; the structural engineer of record selects and applies them for each project.

Section 13

Sizing and Design Calculations

Sizing starts from the hourly cooling load on the design day and the tariff periods. The formulas below give a first estimate; a full design uses 8,760-hour simulations and the OEM's selection data.

13.1Cooling units

TR·h to thermal kWh

E (kWh(th)) = TR·h × 3.517

10,000 TR·h × 3.517 ≈ 35,170 kWh(th) ≈ 35.2 MWh(th)

Indian HVAC quotes storage in ton-hours; engineers often need it in kWh to compare with tariffs and batteries.

Symbol	Meaning
TR·h	Ton-hours of cooling stored
3.517	kW of cooling per ton of refrigeration

13.2Chilled-water volume

Tank water volume

V = E ÷ (1.163 × ΔT × FoM)

35,170 kWh ÷ (1.163 × 8 × 0.9) ≈ 4,200 m³ (≈ 3,780 m³ at FoM 1.0)

Each cubic metre of water gives 1.163 kWh per kelvin of temperature difference. Divide by the figure of merit for real-tank losses.

Symbol	Meaning
V	Water volume (m³)
E	Stored cooling (kWh(th))
ΔT	Return minus supply (K)
FoM	Figure of merit, 0.85–0.95

13.3Ice mass and tank volume

Ice needed

m = E × 3,600 ÷ 334 ; V(ice) = m ÷ 917 ; V(tank) = V(ice) ÷ packing factor

35,170 kWh → 379 t of ice → 413 m³ of ice → ≈ 830 m³ of tank at packing 0.5

Ice holds 334 kJ/kg as latent heat and has a density of about 917 kg/m³. Only part of a tank can be ice — coils, capsules and free water take the rest — so a packing factor of about 0.4–0.6 is used.

Symbol	Meaning
m	Mass of ice (kg)
334	Latent heat of fusion (kJ/kg)
917	Density of ice (kg/m³)
packing factor	Share of tank volume that becomes ice

13.4Chiller size

Chiller for full storage and for load levelling

Full storage: TR = stored TR·h ÷ charging hours ; Load levelling: TR ≈ daily TR·h ÷ 24

10,000 TR·h ÷ 10 h = 1,000 TR (before ice-duty derating of ≈ 20–35 %)

In full storage the chiller must refill the whole store in the off-peak window. In load levelling the chiller runs all day at the average load and the store covers the difference. A chiller making ice delivers less than its nameplate, so its nominal rating is larger.

Symbol	Meaning
TR	Chiller capacity (tons of refrigeration)
charging hours	Hours available to recharge

13.5Worked example — load levelling

Store for load levelling

Store = Σ (hourly load − chiller TR) over hours when load > chiller

Office: 1,500 TR for 12 h = 18,000 TR·h/day → chiller 750 TR running 24 h → store (1,500 − 750) × 12 = 9,000 TR·h

The chiller halves from 1,500 TR to 750 TR. At night it fills the store with 9,000 TR·h; by day it runs at 750 TR and the store adds the other 750 TR.

Symbol	Meaning
Σ	Sum over the hours

13.6Peak demand saving

kW taken off the peak

ΔP = TR shifted × whole-plant kW/TR

1,000 TR shifted × 0.9 kW/TR ≈ 900 kW off the peak

Multiply the cooling moved out of the peak by the electricity the whole plant (chillers, pumps, towers) uses per ton. This is what lowers the maximum-demand charge.

Symbol	Meaning
ΔP	Peak demand saved (kW)
kW/TR	Whole-plant specific power, typically 0.8–1.2

13.7Live estimator

Enter the cooling you want to store (TR·h), the chilled-water temperature difference (K) and the hours available for charging. The estimator returns the stored cooling in kWh(th) (TR·h × 3.517), the chilled-water volume needed (kWh ÷ 1.163 ÷ ΔT), the ice-tank volume (latent heat 334 kJ/kg, ice density 917 kg/m³, packing factor 0.5) and the chiller size in TR to recharge a full store in the charging hours. It is a first estimate only: it ignores the figure of merit, heat gains and ice-duty chiller derating.

Estimate

Stored cooling: 70,340 kWh(th)
Chilled-water tank volume: 7,562 m³
Ice tank volume: 1,654 m³
Chiller size for full storage: 2,000 TR

Water 4,186 kJ/m³·K; ice 334 kJ/kg at 917 kg/m³ with a 0.5 packing factor. Ice-making chillers lose some capacity at −5 °C; add tank margin of 10–15 %. Preliminary screening only; BARREL confirms any figure with a site study.

All worked examples use rounded, indicative values. Real designs add heat gain through the tank (1–3 % a day), pump heat, ice-duty derating and a safety margin of 10–15 %.

Section 14

Engineering Deliverables Register

A cold-storage project produces a predictable set of studies, drawings and documents. This register is what BARREL can prepare or check for an owner, consultant or lender.

14.1Typical deliverables

Typical deliverables
Stage	Deliverable	Purpose
Feasibility	Cooling load and tariff study (hourly, 8,760 h where data allow)	Shows the savings and the right strategy
Feasibility	Options report: ice, chilled water, PCM, none	Compares cost, space and savings
Basic design	Process flow diagram and P&ID	Fixes modes, valves and tie-ins
Basic design	Tank sizing and stratification / ice-build calculation	Confirms storage capacity
Basic design	Equipment list and data sheets	Chillers, pumps, HX, tank, coils
Detailed design	Hydraulic calculation and pump selection	Flow, head and NPSH
Detailed design	Civil and structural drawings for the tank	Foundations, walls, seismic
Detailed design	Electrical single-line diagram and load list	Feeders, VFDs, metering
Detailed design	Control philosophy and sequence of operations	How every mode switches
Detailed design	Insulation and heat-gain calculation	Daily standing loss
Procurement	Technical specifications and bid evaluation	Fair, comparable bids
Construction	Inspection and test plan (ITP), method statements	Quality during build
Commissioning	Test procedures, hydrotest, performance test report	Proof of capacity
Handover	As-built drawings, O&M manual, M&V baseline	For the operator and auditor

PFD
P&ID
SLD
Sequence of operations
Tank GA
Diffuser drawings
ITP
FAT / SAT
M&V plan
As-builts

Section 15

Site Selection and Feasibility

Cold storage pays when there is a large cooling load, a clear gap between peak and off-peak power prices (or a high demand charge), and room for a tank. A short feasibility study answers whether all three are present.

15.1What the study looks at

Load

Peak and daily cooling (TR, TR·h)
Day-to-night ratio
Seasonal swing
Future expansion

Tariff

ToD peak, normal and solar-hour rates
Maximum-demand charge (₹/kVA per month)
Contract demand and penalties
Open-access or rooftop solar

Space and site

Basement, roof, ground or car-park space
Floor and soil bearing capacity
Crane and delivery access
Visual and planning limits

Existing plant

Chiller age and type
Can chillers make ice?
Pump and pipe capacity
BMS capability

Risk

Need for cooling ride-through
Water availability and quality
Fire-water rules
Downtime allowed for tie-ins

Finance

Capex budget or service model
Payback target
Subsidies or green-finance options
Who owns and operates

15.2Quick screening rules (indicative)

Quick screening rules (indicative)
Signal	Good candidate	Weak candidate
Peak cooling load	Above about 300–500 TR	Below about 100 TR (PCM may still suit)
Peak-to-off-peak price gap	₹2–4/kWh or more	Little or no ToD difference
Demand charge	High, and set by the cooling peak	Low, or set by other loads
Load shape	Strong afternoon peak, quiet nights	Flat 24-hour load (except for ride-through)
Space	Room for a tank or ice modules	No space and no structural margin
New build or chiller replacement	Yes — chiller downsizing adds savings	Recently installed oversized chillers

15.3Feasibility steps

1Collect 12 months of power bills and 2–4 weeks of chiller logs
2Build the hourly load profile and match it to tariff periods
3Screen ice, chilled water and PCM against space and supply temperature
4Size options and estimate capex, opex and savings
5Sensitivity on tariff changes and load growth
6Recommend a configuration and a delivery model

Screening thresholds are rules of thumb only; the actual result depends on the state tariff order and the site's load profile.

Section 16

Turnkey EPC, Packages and Supply Chain in India

Cold storage is delivered like a chiller-plant project with a large civil element. BARREL can take it from study to handover as one turnkey contract, or deliver selected packages with the owner's consultant.

Most equipment is available in India: chillers, pumps, cooling towers, heat exchangers, valves, insulation, steel and concrete tanks are made locally. Ice coils, ice-ball capsules and some PCMs are made in India or imported through OEM partners.

16.1Project phases

1Feasibility and option study
2Basic design, budget and permits
3Detailed engineering
4Procurement and factory tests
5Civil works and tank construction
6Mechanical, electrical and controls installation
7Hydrotest, flushing, glycol fill and commissioning
8Performance test, handover and M&V

16.2Work packages

Work packages
Package	Scope
Civil and structural	Soil tests, foundations, tank or pit, plinths, trenches, plant room
Storage	Steel / concrete tank, diffusers, ice coils or capsules, insulation, cladding
Mechanical	Chillers, pumps, heat exchangers, cooling towers, piping, valves, water treatment
Electrical	LT panels, VFDs, cabling, earthing, lighting, metering
Controls	PLC / BMS, sensors, SCADA, tariff logic, remote monitoring
Testing and commissioning	Hydrotest, flushing, balancing, performance test

16.3Delivery models

Turnkey EPC

One contract, one price, one point of responsibility to handover.

EPCM

BARREL manages design and procurement; the owner places contracts.

Design-build packages

Storage package alone, tied into an existing plant.

Build-own-operate

BARREL or an investor owns the plant and sells cooling per TR·h.

16.4Supply chain in India (indicative)

Supply chain in India (indicative)
Item	Availability	Lead time (indicative)
Water-cooled and air-cooled chillers	Made in India by several manufacturers	12–24 weeks
Glycol / ice-duty chillers	India and import	16–30 weeks
Pumps, valves, heat exchangers	Made in India	6–16 weeks
Cooling towers	Made in India	8–14 weeks
Steel tank plates, concrete, insulation	Local	Build period 3–9 months
Ice-on-coil modules, ice balls	India and import through OEM partners	12–24 weeks
PCM capsules and panels	Indian start-ups and import	8–20 weeks
BMS and PLC hardware	India and import	6–12 weeks

Lead times are typical market ranges and change with demand; firm dates come from the purchase orders.

Section 17

Testing, Commissioning and Operations & Maintenance

Commissioning proves that the store holds its rated TR·h and discharges at its rated rate. After that, savings depend on the plant being run to the tariff every day and on water and glycol being kept in good condition.

17.1Testing and commissioning

1Factory tests on chillers, pumps and panels (FAT)
2Tank hydrotest and leak check; insulation inspection
3Pipe flushing, chemical cleaning and passivation
4Glycol fill and concentration check
5Instrument calibration (temperature string, flow, BTU, level)
6Mode-by-mode functional tests of the controls
7Full charge and full discharge test on a design-type day
8Capacity and stratification report (FoM) or ice-inventory check
9Training, O&M manuals and handover

17.2Routine maintenance (indicative)

Routine maintenance (indicative)
Task	Frequency
Check charge / discharge log and peak shaved	Daily (automatic report)
Water treatment test and dosing	Weekly to monthly
Glycol concentration and inhibitor check	Quarterly to six-monthly
Tank temperature-string calibration	Yearly
Chiller service, tube cleaning	Yearly or as per OEM
Insulation and cladding inspection	Yearly
Tank internal inspection	Every 5–10 years
Control-strategy review against new tariff orders	Yearly or when tariffs change

17.3Performance indicators to track

TR·h charged and discharged per day
Peak kW avoided and maximum demand per month
Whole-plant kW/TR in charge and discharge modes
Tank figure of merit or ice-build completeness
Daily standing loss (heat gain)
₹ saved versus baseline, verified each month

Frequencies are typical; the OEM manuals and the site's water quality set the final maintenance plan.

Section 18

Safety and Risk

Ice and chilled-water storage are among the safest forms of energy storage: the medium is water, the temperatures are mild and nothing can burn or explode. The real risks are structural (a very heavy tank), water leakage, glycol handling, refrigerants in the chiller plant, and — for cryogenic systems — extreme cold and pressure.

18.1Hazards and controls

Hazards and controls
Hazard	Where	Control
Structural failure or leak	Large tanks	Proper foundation and seismic design, hydrotest, bunding, inspection
Flooding of basements	Pits and basement tanks	Leak detection, sumps, waterproofing, high-level alarms
Glycol exposure	Ice systems	Prefer propylene glycol near food; spill kits; labelled pipes
Refrigerant leak	Chiller plant rooms	Leak detectors, ventilation, ASHRAE 15 / ISO 5149 practice; ammonia plants need special care
Legionella and bacteria	Cooling towers, open tanks	Water treatment, dosing, regular testing
Cold burns and asphyxiation	Cryogenic (LNG, liquid nitrogen)	PPE, oxygen monitors, ventilation, PESO-approved vessels
Confined spaces	Tank entry	Permit-to-work, gas testing, rescue plan
Working at height	Tank roofs	Guard rails, harness, ladders with cages

18.2Project and business risks

Tariff change

A new tariff order may narrow the peak / off-peak gap. Controls must be reprogrammable and savings reviewed yearly.

Load change

Tenancy, occupancy or process changes alter the load profile; design with some flexibility.

Poor operation

Stores left full or empty at the wrong time save nothing. Automatic control and monitoring are essential.

Section 19

Standards and Compliance

There is no single cold-storage standard; the project follows HVAC, tank, structural, electrical, refrigerant and building codes. The list below shows the usual references in India and abroad.

19.1International references

International references
Reference	Covers
ASHRAE Handbook — HVAC Applications, Thermal Storage chapter	Design of ice, chilled-water and PCM storage
ASHRAE Design Guide for Cool Thermal Storage	Detailed sizing and system design
ANSI/ASHRAE Standard 150	Method of testing the performance of cool storage systems
AHRI Standard 900	Performance rating of thermal storage equipment used for cooling
ASHRAE Standards 15 and 34 / ISO 5149	Refrigeration system safety and refrigerant classification
API 650, AWWA D100, AWWA D110 / D115	Welded steel and prestressed concrete water tanks
ASHRAE TC 9.9 thermal guidelines	Data-centre temperature ranges
ISO 21009 / EN 13458	Static cryogenic vessels

19.2Indian codes and regulators

Indian codes and regulators
Reference	Covers
National Building Code of India 2016 (Part 8, Building Services)	HVAC, plumbing, fire and building services
ECBC 2017 and ECSBC 2024 (Bureau of Energy Efficiency)	Energy efficiency of commercial buildings, including HVAC
IS 456, IS 3370	Reinforced concrete; concrete structures for retaining liquids
IS 800, IS 803	Structural steel; vertical steel storage tanks
IS 1893, IS 875	Seismic and other design loads
IS 659, IS 660	Safety codes for air-conditioning and mechanical refrigeration
BEE star labelling for chillers	Chiller efficiency ratings
PESO — SMPV (Unfired) Rules 2016	Cryogenic and pressure vessels, LNG and liquid nitrogen
CEA safety regulations and state electrical inspectorate	Electrical installations
State fire services	Fire-water use of tanks and plant-room fire safety

Code editions change; the project specification fixes the edition to be followed. The list is a guide, not a full compliance register.

Section 21

Commercial Models, Cost and Investment

Cold storage earns its money from three sources: lower energy charges (buying cooling power at night or solar-hour rates), lower maximum-demand charges, and — in new buildings — smaller chillers, transformers and DG sets. Payback is often 3–7 years in India where the tariff gap is wide.

21.1Indicative installed cost of the storage element

Indicative installed cost of the storage element
Medium	Indicative cost (storage only)	Cost trend with size
Large chilled-water tank (> 20,000 TR·h)	₹5,000–15,000 per TR·h	Falls sharply with size
Small chilled-water tank (< 5,000 TR·h)	₹12,000–30,000 per TR·h	High per TR·h at small scale
Ice-on-coil / encapsulated ice	₹8,000–25,000 per TR·h	Moderate fall with size
PCM systems	₹15,000–40,000 per TR·h	Depends on material and packaging

21.2Annual saving

Simple saving estimate

Saving = (kWh shifted × price gap) + (kVA cut × demand charge × 12) − extra kWh × price

900 kW × 6 h × 300 days × ₹3 ≈ ₹49 lakh + 900 kVA × ₹400 × 12 ≈ ₹43 lakh → about ₹90 lakh a year before losses

Energy moved from peak to off-peak earns the tariff gap; the lower peak cuts the monthly demand charge. Subtract the small extra energy for ice-making or tank losses.

Symbol	Meaning
price gap	Peak minus off-peak tariff (₹/kWh)
demand charge	₹ per kVA per month
extra kWh	Additional energy for ice-making and losses

21.3Commercial models

Owner capex

The owner buys the plant; BARREL delivers EPC and optional O&M.

Cooling-as-a-service

An investor owns the plant; the site pays per TR·h of cooling delivered, with no upfront cost.

Shared savings / ESCO

Savings against a verified baseline are shared for a fixed term.

District cooling tariff

Connection charge plus capacity and energy charges per TR and TR·h.

Green finance

Energy-efficiency loans and green bonds; cold chain can tap government cold-chain schemes.

Bundled with solar

Rooftop or open-access solar plus cold store sold as one package.

21.4Investment risks and mitigation

Investment risks and mitigation
Risk	Mitigation
Tariff gap narrows	Sensitivity analysis; solar-hour strategy; contract with tariff-change clause
Load lower than forecast	Measured baseline; modular ice tanks that can be added later
Underperformance	Performance test at handover; liquidated damages; M&V each month
Customer credit (service models)	Security deposit, escrow, step-in rights
Technology risk	Proven media (water, ice) for most projects; PCM only with cycle-test data

Costs, tariffs and savings are indicative 2024–26 ranges for illustration; actual numbers depend on site, scale, state tariff order and scope. They are not a quotation.

Section 22

India and Global Markets and Policy

India's cooling demand is expected to grow several-fold over the next two decades as incomes rise and summers get hotter. The India Cooling Action Plan, time-of-day tariffs and the cold-chain push all point towards storing cold.

22.1India policy drivers

India policy drivers
Policy	What it says	Why it matters for cold storage
India Cooling Action Plan (MoEFCC, 2019)	20-year plan to 2037–38: cut cooling demand 20–25 %, refrigerant demand 25–30 % and cooling energy 25–40 %	Thermal storage and district cooling are among the efficiency levers
Electricity (Rights of Consumers) Amendment Rules 2023	Time-of-day tariff for C&I consumers (from April 2024) and most others (from April 2025); solar-hour rate at least 20 % below normal, peak rate higher	Creates the price gap that cold storage earns
ECBC 2017 / ECSBC 2024	Energy-efficiency rules for commercial buildings	Rewards efficient chiller plants and load management
Cold-chain schemes (MoFPI, MIDH, NCCD)	Support for integrated cold chains, pack houses and cold rooms	PCM and ice-bank cold rooms for farm produce
Smart Cities and new townships	Planned districts with central utilities	District cooling with large tanks
Demand response and DISCOM programmes	Peak-load management pilots	Cold stores are natural, flexible loads

22.2Global picture

United States

Ice storage common in offices since the 1980s
Many universities run large chilled-water tanks
Utility demand-charge and rebate programmes

Gulf and Asia

Gulf states: large district cooling with chilled-water storage
Singapore and Malaysia: district cooling in business districts
China and Korea: policy support for ice storage in buildings

Trends

Coupling with solar and heat pumps
Larger tanks for data-centre campuses
LNG cold recovery at new terminals
PCM cold chain for emerging markets

22.3Indian market segments to watch

Data-centre campuses in Mumbai, Chennai, Hyderabad, Noida and Pune
Airports, metro depots and large hospitals
Malls and commercial office parks
Pharma and vaccine cold chain
Dairy and farm-produce cold rooms in rural areas
District cooling in new business districts and GIFT City-style developments

Policy summaries are simplified; read the notified rules and the state tariff order before relying on any figure.

Section 23

Frequently Asked Questions and References

Plain answers to the questions owners and facility managers ask most, and where to read more.

23.1Questions and answers

Is cold storage the same as a battery?

No. It stores cooling, not electricity. But because chillers are a large electric load, shifting cooling to off-peak hours has a similar effect on the bill and the grid, usually at lower cost per kWh shifted.

Does cold storage save energy or only money?

Mostly money — it moves energy to cheaper hours. Ice-making uses a little more energy; chilled-water storage is close to neutral. Night charging with cooler condenser water and steady chiller loading can partly or fully offset the losses.

Ice or chilled water — which is better?

Chilled water is cheaper per TR·h at large scale and uses normal chillers, but needs 3–5 times the space. Ice suits buildings with limited space or a need for very cold supply water.

How big a tank do I need?

Divide the cooling you want to store (TR·h × 3.517 = kWh) by about 9 kWh per m³ for chilled water at 8 K, or about 40–50 kWh per m³ of tank for ice. The live estimator on the Sizing tab does this for you.

What is a TR·h?

One ton of refrigeration for one hour — 3.517 kWh of cooling. A 1,000 TR plant running for 8 hours delivers 8,000 TR·h.

Can my existing chillers make ice?

Some can, with glycol and new set-points, but many standard chillers cannot run below about 4 °C leaving water. A study of the existing plant answers this; often a dedicated ice-duty chiller is added.

How long does the cold last?

A well-insulated tank loses only 1–3 % of its stored cooling a day, so a daily cycle loses very little. Stores are normally cycled every day.

What is the payback?

Typically 3–7 years in India where the peak / off-peak gap and demand charges are significant, and shorter in new buildings where chillers can be downsized. It must be checked against your own tariff.

Does the new time-of-day tariff help?

Yes. The 2023 consumer rules require time-of-day tariffs for commercial and industrial consumers, with cheaper solar hours and dearer peak hours. That gap is what cold storage earns.

Can I charge the store with solar power?

Yes. A store charged during the day from rooftop or open-access solar can cover the evening peak, increasing solar self-use and cutting export or curtailment.

Is it safe?

Ice and chilled water are among the safest storage forms — no fire or explosion risk. The engineering risks are structural loads, leaks, glycol handling and refrigerants, all managed by normal codes.

Can the tank be used for fire water?

Often yes, with the approval of the fire authority and suitable connections, which can save the cost of a separate fire tank.

Why do data centres use chilled-water tanks?

When the power fails, chillers take several minutes to restart even after generators start. A tank, with pumps on UPS, keeps the servers cool during that gap.

What is district cooling?

One central chiller plant makes chilled water and pipes it to many buildings. Large storage tanks let the plant run steadily and cut its peak demand.

What is LNG cold recovery?

LNG at about −162 °C must be warmed to gas at import terminals. Using that cold for air separation, freezing or cooling instead of wasting it to sea water saves energy.

Where do PCMs make sense?

Where a specific temperature must be held without power — vaccine and pharma storage, cold rooms with power cuts, reefer trucks — or where space is too tight for water.

Can I pay per unit of cooling instead of buying the plant?

Yes. In a cooling-as-a-service model an investor owns and runs the plant, and the site pays per TR·h delivered.

How long does a project take?

Modular ice tanks can be installed in 3–6 months; a large chilled-water tank with a new plant typically takes 9–18 months from design to handover.