One refrigeration system, carried from heat load to issued reports.

The heat load sets the cycle’s duty, the cycle’s flows size the pipes, the pipes fill in the charge — each station of Kelvin’s calculation chain starts from the one before it. Below, one example system is worked through Kelvin’s own calculation code.

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A sample practice’s six jobs, open in the real app. No account; nothing you change is kept.

Example system: Chiller (MT) room8 × 6 × 3.5 m at 2.0 °C · single stage
Refrigerant: R-134a
Load: 10.16kW
SST: −4.0°C
SCT: 45.0°C
COP: 3.10

Example system. Every figure on this page is Kelvin’s calculation code run on the inputs each station lists; R-134a properties are the Refrigerant Library’s migrated record. Metric units.

Heat Load

Transmission, infiltration, product

Takes: Heat Load’s defaults for a Chiller (MT) room: 8 × 6 × 3.5 m at 2.0 °C and 85% RH, 35.0 °C outside, 100 mm PIR panel, one 1.8 × 2.4 m sliding door with a strip curtain; the example’s product is 5,000 kg of milk (whole) pulled down from 15.0 °C over 24 h.

Heat Load readings for the example system
Reading	Value	Basis
TransmissionU × A × ΔT for each wall, the ceiling and the floor	1.52kW	U × A × ΔT for each wall, the ceiling and the floor
InfiltrationDoorway method, strip curtain	0.90kW	Doorway method, strip curtain
ProductPull-down over 24 h	3.05kW	Pull-down over 24 h
InternalLighting, occupancy, material handling equipment	0.68kW	Lighting, occupancy, material handling equipment
Governing casePull-down; holding is 3.10 kW	6.16kW	Pull-down; holding is 3.10 kW
Design load(6.16 kW + 10% safety) × 24 h ÷ 16 h run time	10.16kW	(6.16 kW + 10% safety) × 24 h ÷ 16 h run time

Defends: The duty the rest of the chain is sized to. Every component is its own line, and the holding and pull-down cases are both solved, so the plant is sized to whichever governs.

Cycle

Single stage · R-134a

Takes: 10.16 kW and −4.0 °C SST handed over from Heat Load (the 2.0 °C room less the preset’s 6.0 K TD), 45.0 °C SCT at 35.0 °C design ambient, 5.0 K superheat, 5.0 K subcooling and isentropic η 0.70.
Model: Vapour-compression model on saturation properties interpolated from NIST Chemistry WebBook tables for the refrigerant (NIST Standard Reference Database 69; IIR reference state, h = 200 kJ/kg for saturated liquid at 0 °C), compression on the same table's saturated vapour carried into superheat along each isobar (Peng & Robinson 1976 residual properties, scaled to the table's own vapour heat capacity), the discharge temperature read at the discharge pressure and enthalpy; compression at the entered isentropic efficiency, not a compressor's published performance — design sizing, to be verified against the selected equipment.

Cycle readings for the example system
Reading	Value	Basis
COPCarnot 5.49 · 56.3% of Carnot	3.10	Carnot 5.49 · 56.3% of Carnot
Compressor powerSpecific work 46.61 kJ/kg	3.28kW	Specific work 46.61 kJ/kg
Mass flowRefrigeration effect 144.24 kJ/kg	0.0704kg/s	Refrigeration effect 144.24 kJ/kg
Condenser heatHeat rejection at the condenser	13.44kW	Heat rejection at the condenser
Discharge tempThe temperature the discharge enthalpy sits at, h₂ = h₁ + (h(P₂, s₁) − h₁) ÷ η_s, on real vapour properties (no heat loss)	67.5°C	The temperature the discharge enthalpy sits at, h₂ = h₁ + (h(P₂, s₁) − h₁) ÷ η_s, on real vapour properties (no heat loss)
Compression ratioP_evap 252.7 · P_cond 1159.9 kPa	4.59	P_evap 252.7 · P_cond 1159.9 kPa

Defends: The flows every later station reads: mass flow sizes the pipes, suction density and volumetric efficiency rate the compressor, and condenser heat is the heat-rejection duty.

Pipe Layout

Sized on velocity

Takes: The cycle’s mass flow and conditions, one evaporator on a 20 m drawn run (equivalent-length factor 1.4 suction, 1.3 liquid), and the system’s 8 m discharge and 3 m condenser-to-receiver lines.

Pipe sizes, velocities and statuses for the example system
Line	Size	Velocity	ΔT_sat	Status
Suction1 3/8″ · 20 mΔT_sat 0.44 K	1 3/8″	7.20m/s	0.44K	Pressure not judged
Liquid1/2″ · 20 mΔT_sat 0.42 K	1/2″	0.66m/s	0.42K	Pressure not judged
Discharge5/8″ · 8 mΔT_sat 0.93 K	5/8″	9.39m/s	0.93K	Velocity low
Condenser to receiver5/8″ · 3 mΔT_sat 0.02 K	5/8″	0.41m/s	0.02K	Pressure not judged

Flagged: Discharge line, velocity low. Velocity 9.39 m/s against the discharge band 10.0–18.0 m/s. ΔT_sat 0.93 K; compressor impact is high above 1.0 K and moderate above 0.5 K (sizing code thresholds, no cited source)
Defends: Each line's velocity against its band, its pressure and temperature against the tube maker's rating, the liquid line's subcooling margin before the TXV, and the saturation-temperature penalty on suction and discharge. A line outside a rule is flagged, with the rule it failed.

Equipment

Margin = capacity ÷ duty − 1

Takes: The cycle’s duties — what each pick’s rated capacity is judged against. This example picks no models.

Equipment readings for the example system
Reading	Value	Basis
Evaporator dutyCoolroom load per evaporator · Under 0.9× load per unit undersized; over 1.5× oversized	10.16kW	Coolroom load per evaporator · Under 0.9× load per unit undersized; over 1.5× oversized
Compressor dutyAt −4.0 °C SST, needing 24.60 m³/h swept · Under 0% spare undersized; over 50% spare oversized	10.16kW	At −4.0 °C SST, needing 24.60 m³/h swept · Under 0% spare undersized; over 50% spare oversized
Heat rejectionCompressor power + cooling load · Under 1.0× heat rejection undersized; over 1.5× oversized	13.44kW	Compressor power + cooling load · Under 1.0× heat rejection undersized; over 1.5× oversized

Defends: Every pick against the duty it has to meet, written as spare or short, with the rule it was judged by: evaporators, compressors, condensers, valves, oil separators and receivers alike.

Refrigerant Charge

R-134a

Takes: The sized pipe run. This example picks no equipment, so no equipment charge is counted.

Refrigerant Charge readings for the example system
Reading	Value	Basis
Pipe chargeInternal volume × density at each line's conditions	2.92kg	Internal volume × density at each line's conditions
Liquid lines	2.67kg
Suction lines	0.20kg
Discharge line	0.06kg
Total refrigerantPipe charge; no equipment or receiver in this example	2.92kg	Pipe charge; no equipment or receiver in this example
Total oil2% circulating; no compressor sump counted, as no compressor is picked	0.06kg	2% circulating; no compressor sump counted, as no compressor is picked

Defends: The charge the system is filled to, and the liquid line’s flash margin: 4.6 K of subcooling left after the line’s pressure drop, so no flash gas reaches the TXV.

Operation

A seeded day · design ambient

Takes: A day seeded from the records: 240 door passages at the Heat Load’s traffic, 4 off-cycle defrosts of 20 min, the lighting, people and forklift shifts from 06:00, and the heat load’s batch arriving at 00:00, at the 35.0 °C design ambient all day. The room’s air carries its own heat capacity, 217 kJ/K.
Model: Stand-ins, not picks: a coil rated at the design duty, 10.16 kW at the preset’s 6.0 K TD and linear with TD, and 2 compressors of 12.3 m³/h each, half the swept volume the Cycle station calls for, staged on a 2.0 K suction deadband. No condenser is entered, so the condensing holds the design TD above the air and the fans aren’t judged. The batch is 400 × 300 × 300 mm crates in air at h = 15 W/(m²·K), the example’s assumption.

Operation readings for the example system
Reading	Value	Basis
Peak room airAt 06:15, with the coil off for defrost; set point 2.0 °C	6.4°C	At 06:15, with the coil off for defrost; set point 2.0 °C
Air over set pointBy more than 0.5 K, in the door passages and defrosts; 11.7 h over it at all	7.4h	By more than 0.5 K, in the door passages and defrosts; 11.7 h over it at all
Batch at midnight5,000 kg of milk (whole) from 15.0 °C, by Pham (Ch. 20); the heat load allows 24 h; stock at 2.3 °C	3.5°C	5,000 kg of milk (whole) from 15.0 °C, by Pham (Ch. 20); the heat load allows 24 h; stock at 2.3 °C
Suction142 to 259 kPa g; set point −4.0 °C, 2.0 K deadband	−5.0 to 5.9°C	142 to 259 kPa g; set point −4.0 °C, 2.0 K deadband
Both compressors runningRun hours 19.4 and 7.2; 115 starts — the lead unit short-cycles through the quiet hours on the deadband's 180 s minimum run	3.2h	Run hours 19.4 and 7.2; 115 starts — the lead unit short-cycles through the quiet hours on the deadband's 180 s minimum run
Compressor energyFor the day, delivering 132 kWh of cooling; peak 3.34 kW	40.7kWh	For the day, delivering 132 kWh of cooling; peak 3.34 kW

Defends: What the design does through a day rather than at its design point: whether the room holds its set point through the door traffic and defrosts, how the batch comes down, how the compressors stage and cycle, and where the suction sits. Every figure is the engine's, read at the cursor, and every stand-in and assumption is on the page.

Energy

Brisbane · 16 h a day

Takes: The design re-solved each month at Brisbane’s design ambient for that month (condensing = ambient + 10.0 K, not below 20.0 °C), motor efficiency 0.90, and the heat load’s 16 h a day.

Energy readings for the example system
Reading	Value	Basis
Annual energyCompressor 15,890 kWh; fans not counted	15,890kWh	Compressor 15,890 kWh; fans not counted
Average COPMean of the monthly COPs; every month solved	4.23	Mean of the monthly COPs; every month solved
Peak monthJan	1,594kWh	Jan
Lowest monthJun	1,068kWh	Jun

Not counted: No evaporator or condenser is picked in this example, so fan energy is not counted.
Defends: The running energy the running cost is built on, with each month solved at its own ambient.

BOM & Running Cost

Quantities, not prices

Takes: The charge’s pipe breakdown.

Pipe bill of materials for the example system
Pipe	Length	Pieces	Insulation
1 3/8″ suctionArmaflex AF-34.93-25	20.0m	4× 6 m	Armaflex AF-34.93-25
1/2″ liquidNot insulated by default	20.0m	4× 6 m	Not insulated by default
5/8″ dischargeNot insulated by default	8.0m	2× 6 m	Not insulated by default
5/8″ liquidNot insulated by default	3.0m	1× 6 m	Not insulated by default

Then: Equipment lines come from the picks and pipework from this bill — quantities only. The only money is the running cost: the energy cost and the refrigerant leak cost over the project's years.
Defends: The bill of materials, counted in whole pipe lengths, straight from the design.

Reports

PDF

Takes: The saved record from each station.

Reports Kelvin issues
Report	From
Heat Load report	Heat Load
Cycle report	Cycle
Engineering report, technician guide and tech schedule	Pipe Layout
Equipment report	Equipment
Charge report	Refrigerant Charge
Operation report	Operation
Energy report	Energy
BOM & running cost report	BOM & Running Cost
Project bundle	One PDF, each record's report starting on its own page

Defends: The document the client sees, built from the saved records as PDFs with selectable text. The Reports page names any record in the bundle that has gone stale.

Whole jobs, carried through the same chain

The example above is one room. Each worked example is a whole job: an illustrative brief with its plans, P–h diagram and schematic, and every figure Kelvin’s engine run on the brief.

All worked examples

Transcritical CO₂ supermarket pack, cycle to issued report

An illustrative transcritical CO₂ booster pack for a Brisbane supermarket — 117 kW medium temperature at −8 °C and 31 kW low temperature at −30 °C — carried through Kelvin from heat load to issued report.

Refrigerant: R-744
Gas cooler: 86.3bar
COP: 1.76
Charge: 175kg

Restaurant coolroom and freezer room, each on its own condensing unit

An illustrative walk-in coolroom (1.73 kW at 2 °C) and freezer room (1.36 kW at −18 °C) behind a Melbourne restaurant, each on its own R-454C air-cooled condensing unit — carried through Kelvin from heat load to issued report.

Refrigerant: R-454C
Coolroom: 1.73kW
Freezer room: 1.36kW
Design ambient: 34.8°C

Where requests come from

Requests inbox

Engineering requests raised in Deployr — from a quote, job, asset, site or project — arrive in Kelvin’s Requests inbox, grouped by the client that sent them, once your workspace is paired with Deployr. Deployr is Sentoro’s trade operations platform, a separate product.

Lifecycle

Received
In progress
Awaiting information
Review required
Approved
Report issued
Complete

Steps

ReviewDone once the status has moved on from Received
ContextDone once Deployr's context is on the request
Link designDone once a system design is linked
Selection & pushDone once a push has been sent to Deployr
IssueDone once reports have been emailed to the client

No account needed: refrigerant pressure–temperature tables and P–h diagrams for 28 refrigerants, with each one’s GWP, ODP and safety class; a superheat and subcooling calculator and printable P–T charts; and the worked examples.

Put your own system through the chain

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Note

Verify before implementation

Kelvin’s calculations are design aids based on published industry methods and standard thermodynamic and hydraulic models. They do not constitute automatic compliance with AS/NZS, EN or other codes — every result, including the example on this page, must be verified by a qualified refrigeration engineer before implementation.