Practical Refrigeration Formulas & Calculations [With Examples]

Refrigeration Capacity and Cooling Load Calculations

To achieve optimal cooling, you need to calculate how much heat to remove from a space, which requires the refrigeration capacity and cooling load formulas.

These formulas help you with repairs, equipment sizing, and upgrades. 

Refrigeration capacity formula 

The refrigeration capacity formula calculates the total heat energy you need to remove to cool a substance. It’s used for sizing systems like cold rooms or chillers by giving you the raw load in BTUs or kilowatts.

Formula: Q = m × Cp × ΔT

Symbols:

• Q = Heat removed (BTUs or kW)

• m = Mass (lbs or kg)

• Cp = Specific heat (how hard it is to change temperature)

• ΔT = Temperature difference

Example: Let’s say you’re cooling 100 lbs of fresh vegetables from 70°F to 35°F, and you want to find out how much heat to remove from the space. 

Since the Cp (specific heat) of vegetables is about 0.5 BTU/lb·°F, multiply 100 by 0.5 and the temperature difference, which is 35. So, you must remove 1,750 BTUs of heat from the walk-in chiller.

Q = 100 × 0.5 × (70 – 35) Q = 100 × 0.5 × 35 = 1,750 BTUs

Cooling capacity formula

Cooling capacity tells you how much cooling power a system has, usually in tons. It's helpful in selecting or comparing AC and refrigeration units.

Formula: Tons = BTU/hr ÷ 12,000 1 ton of cooling = 12,000 BTU/hr (based on melting a ton of ice over 24 hours)

Example: You need to choose an A/C that has the cooling capacity to provide 36,000 BTU/hr of cooling for a conference room. 

You need to divide 36,000 by 12,000 to get 3 tons of cooling capacity. 

Refrigeration BTU formula

This converts mass, temperature change, and specific heat into a BTU/hr value for estimating cooling loads in ducted systems.

Formula: BTU = lbs × ΔT × Cp

This formula is useful when you know the weight of the material and by how much you want to cool it.

Example: How much energy in BTUs will be required to cool 200 lbs of water from 100°F to 50°F? Since the specific heat (Cp) of water is 1 Btu/lb°F, multiply 200 x 50 x 1 to get 10,000 BTUs as the energy required to achieve that cooling.

Use ServiceTitan’s Refrigeration BTU Calculator to simplify this step in the field.

Once you know how much cooling is required using the formulas explained above, the next step is understanding how the refrigeration system delivers the cooling and how efficiently it does that.

Refrigeration Effect and System Efficiency Formulas

These formulas calculate how well a system cools. We’ll discuss how the Refrigeration Effect and COP (Coefficient of Performance) formulas measure cooling system efficiency.

Refrigeration Effect formula

This shows how much heat the refrigerant evaporator absorbs, in Kg/J. It is used to compare refrigerants and optimize system performance in cycle design.

Formula: RE = h1 – h4

Symbols:

• h1 = Enthalpy before evaporator

• h4 = Enthalpy after expansion valve

Example: You want to choose between two refrigerants for a fresh foods walk-in chiller. The first one has h1 = 130, h4 = 50. 

So, the RE (refrigerant evaporator) is 80 units when you subtract 50 from 130. 

When you calculate the RE for the second refrigerant, you may want to choose a refrigerant that gives a higher RE, as it absorbs more heat per cycle.

But a higher RE is not all that counts when choosing a chiller. The Coefficient of Performance also plays a key role.

Coefficient of Performance (COP)

The Coefficient of Performance (COP) tells you how much cooling a refrigeration system gives per unit of energy consumed.

Formula: COP = RE ÷ Work input

Higher COP = better efficiency. This formula is useful in energy audits or retrofits.

Example: You’re comparing two chillers for a large cold storage facility. One of the chillers has RE = 80, and requires a work input of 20.

The COP will be 4, which is what you get when you divide 80 by 20.

This means that even though a chiller may have a higher RE, it should only be considered if it also has a higher COP. 

Understanding how much work your system is doing leads right into the heart of the machine, which is the compressor.

Let’s dive into some compression formulas. 

Compressor Calculations and Work Input

The compressor is the engine of your refrigeration system. These calculations help you estimate its capacity and energy requirements.

Refrigeration compressor capacity calculation

The refrigeration compressor capacity calculation tells you how much refrigerant the compressor can handle at a time. It’s needed for sizing and performance verification.

Formula: Compressor Capacity = Volumetric efficiency × Swept volume × RPM

Symbols: RPM = revolutions per minute, which measures the compressor’s speed.

Make sure to check your manufacturer's specs for swept volume and efficiency.

Example: You need to size a replacement compressor for a walk-in freezer. If swept volume = 6 CFM, VE = 0.8, and RPM = 1,800:

Compressor Capacity = 0.8 × 6 × 1,800 = 8,640 CFM

Compressor work formula

The compressor work formula helps you estimate how much power the compressor consumes. It calculates the energy input the compressor requires (in kW or BTU/hr). It’s often used together with COP or power meter readings.

Formula: Work = (P2 × V2 – P1 × V1) ÷ (n – 1) (Ideal gas law)

Symbols:

P1 = Initial pressure of the gas (before the process), typically in Pascals (Pa)

P2 = Final pressure of the gas (after the process), in Pascals (Pa)

V1 = Initial volume of the gas (before the process), in cubic meters (m³)

V2 = Final volume of the gas (after the process), in cubic meters (m³)

N = Polytropic index (also called the exponent)

But realistically, nobody’s figuring out P1, V1, on a rooftop unit at 3 p.m. in August. In real life, you measure power in kW directly using a power meter or clamp-on amp probe and convert it if needed.

So, during field work, use a clamp meter on the power leads and multiply volts × amps × power factor, or get a meter that directly gives you real kW.

This is useful for performance testing and energy cost estimates. It can be used to determine whether a compressor is oversized or undersized for a given load, especially when you already suspect an inefficiency but need real numbers to prove it.

Example: Let’s say you’re on-site checking out a commercial refrigeration system that’s been underperforming.

You measure:

• Power input: 5 kW (read via clamp meter on compressor wiring)

• Cooling delivered: 80 kW (from RE × mass flow or BTU conversion)

COP = 80 ÷ 5 = 16

This COP shows that the system is efficient. You can now document or log that in and check other parameters.

Now let’s move into system-level design, where you calculate what the entire system needs to handle.

Industrial Refrigeration Formulas for System Design

Designing a full system means calculating the amount of heat rejected, the flow of refrigerant, and the charge needed.

Heat rejection in the condenser

Heat rejection in the condenser calculates the heat load on the condenser. It measures the total heat the condenser needs to reject.

Formula: Q = RE + Compressor Work

This value is important for sizing condensers, cooling towers, or water-cooled systems.

Example: You need to design condenser units for an industrial ammonia chiller.

If RE is 100, and compressor work = 25, then the heat rejected is 125 units, obtained by adding the values.

Q = 100 + 25 = 125 units

Volumetric flow rate of refrigerant

The volumetric flow rate of refrigerant determines the refrigerant volume flow rate through piping, which tells you how much refrigerant flows through the system per unit of time.

Formula: Flow rate = Mass flow rate ÷ Refrigerant density

Symbols:

• Mass flow rate is in lb/min or kg/min

• Density is in lb/ft³ or kg/m³

• Result is in ft³/min or m³/hr

This formula is important for pipe sizing, valve or line selection, and system pressure drop evaluation. 

Example: You’re engineering a commercial R-404A refrigeration system for a walk-in freezer. Your design calls for a mass flow rate of 12 lb/min. At evaporator conditions, R-404A has a density of 0.06 lb/ft³ in vapor form.

Volumetric Flow Rate = 12 lb/min ÷ 0.06 lb/ft³ = 200 ft³/min

So, your suction line must accommodate 200 ft³/min of refrigerant vapor. Your manufacturer has to choose a suction pipe size that handles 200 ft³/min. 

You'd repeat this logic on the discharge line, accounting for different temperatures and pressures (which change refrigerant density).

Refrigeration line charge formula

The refrigeration line charge formula helps estimate the total amount of refrigerant required in the suction or liquid lines. You need it when adding or adjusting refrigerant during install/startup. 

Formula: Charge = Volume of piping × Density of refrigerant

The formula is useful when commissioning a system, verifying a charge during retrofits, and ensuring proper function of TXVs (thermostatic expansion valves), compressors, and evaporators.

Example: You're installing a split rooftop system with a 60 ft refrigerant line set (suction and liquid lines). You're using R-410A, and the system includes a 3/8" OD liquid line and 7/8" OD suction line.

From copper tubing specs:

• 3/8" liquid line holds approx. 0.0064 ft³/ft

• 7/8" suction line holds approx. 0.0255 ft³/ft

So total internal volume is:

(60×0.0064) + (60×0.0255) = 0.384 + 1.53 = 1.914 ft³

R-410A liquid density at 100°F ≈ 69 lb/ft³

Line Charge = 1.914 x 69 = 132.0 lbs

You should add a buffer (often 10–20 percent) to accommodate system components and ensure a full liquid column in the liquid line.

Let’s now go to the final group of formulas for field diagnostics. 

Field Diagnostics and Performance Tuning

When your system is live, diagnostics like superheat and subcooling formulas tell you what’s happening inside. 

Superheat calculation

Superheat indicates how much additional heat the refrigerant gains past boiling. It verifies if the refrigerant is fully vaporized before hitting the compressor. Calculating the superheat will help you prevent compressor slugging.

Formula: Superheat = Suction line temp – Evaporator saturation temp

A low superheat means there’s a risk of flooding, and a high superheat will cause poor cooling.

Example: You want to check the TXV (thermostatic expansion valve) performance in a walk-in cooler. If the suction line temperature is 52°F and the evaporator saturation temp is 40°F, superheat equals 12°F.

Superheat = 52 - 40 = 12°F 

Subcooling calculation

The subcooling calculation measures how much the refrigerant is cooled below its condensation point. It’s used to verify full condenser capacity and correct charge, ensuring the refrigerant is fully condensed before reaching the expansion valve. 

Formula: Subcooling = Condenser saturation temp – Liquid line temp

Example: To charge a split system with a saturation temperature of 100°F and a liquid line temperature of 92°F, subcooling is 8°F.

Subcooling = 100 - 92 = 8°F

Enthalpy from pressure and temperature

Enthalpy from pressure and temperature finds the heat content of the refrigerant using pressure-temperature data and a chart or app. Enthalpy is important in the compressor, capacity, and effect calculations mentioned above.

Formula: Use the pressure + temp + refrigerant chart

Example: Let’s say you’re calculating RE and COP during a system audit, for a pressure of 70 psi and a temperature of 40°F. To arrive at the enthalpy value, you’ll follow these steps:

• Locate Pressure: First, find the given pressure, 70 psi, on the vertical pressure axis. Draw an imaginary horizontal line across the chart at this pressure.

• Locate Temperature: Next, find the temperature, 40°F. Temperature lines (called isotherms) are curved on the chart. You'll find the specific line for 40°F.

• Find the Intersection: The point where the 70 psi horizontal pressure line and the 40°F curved temperature line meet is the thermodynamic state of the refrigerant.

• Read the Enthalpy: From this intersection point, drop a vertical line straight down to the horizontal enthalpy axis. The value where this line intersects the axis is the enthalpy, which in your example is 108 BTU/lb.

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Finally, even the sharpest technicians need more than formulas to succeed. You need tools, training, and the most effective sales tips. 

Empowering Refrigeration Techs Beyond Just Technical Knowledge

If you want to scale your business and thrive in an age when almost everything is digital, these tips will help you stay on top of your game. 

Gear them up with the right technology

While your team may be able to recite all these formulas by heart, you cannot afford the delay and inconsistency that comes with manual calculations. 

Using apps that help techs perform refrigeration calculations is crucial if you charge a flat rate for your services—you're being paid for the job, not the time it takes. If a tech spends extra time doing manual calculations, that time cuts into your profit, not the customer's bill.

ServiceTitan’s Field Service app ticks all the boxes for an ideal efficiency-boosting tool.

The app allows you to:

• Build checklists for superheat, subcooling, charge validation, and leak tests.

• Calculate refrigeration BTU and log every diagnostic and standardized test across the team.

• Take photos of pressure gauges, line sets, coils, and leaks.

• Automatically upload live job statuses, notes, and estimates.

• See past repairs, refrigerant types, and prior performance issues.

• Save client information in one centralized platform for all team members to reference.

That way, your team spends less time doing paper-based calculations and more time fixing problems with complete visibility into what they’ve done and what needs to be done next.

Still not convinced about integrating ServiceTitan to boost your efficiency? Check out Cockburn Refrigeration’s story and how ServiceTitan increases their employee efficiency and productivity.

Teach them effective selling techniques

You don’t want your skilled techs struggling to explain why a customer should approve an upsell, maintenance contract, or equipment upgrade.

They need to learn how to negotiate with clients, explain value, and give the best estimates. Their presentation skills and understanding of your services must be top-notch, so they can present offers to customers in a way that convinces them to sign on the dotted line.

ServiceTitan helps you achieve this through its Pricebook Pro and automation features.

Firstly, it suggests various ways to upsell customers. 

For example, the app reminds techs to discuss upgrades if the cooling system is outdated (e.g., R-22).

It allows techs to present tiered options for repairs, maintenance, or replacements so that customers can choose what they prefer. 

Additionally, techs can switch to ServiceTitan’s presentation interface during sales conversations, so customers can visually compare options and select one that matches their budget.

Once customers pick an option and agree to the terms, technicians can enroll them in their chosen plan with just a single click. 

If it’s a one-time purchase, techs can instantly generate a flat-rate estimate without leaving the job site.

Even better, prices quoted in the estimate or membership plan are guaranteed to be accurate, since all prices in our Pricebook automatically change whenever manufacturers update theirs.

Lastly, the Field Service App boosts techs’ efficiency and productivity by:

• Auto-calculating energy savings for new systems.

• Sending automated reminders, discounts, and priority service deals.

• Granting them access to all the information they need for the job so they don’t have to sort through piles of paper documents.

Over to You

To repair and maintain cooling systems, knowing the math behind their operation is crucial. Whether you're sizing equipment, diagnosing issues, or designing a system, knowing the right formulas—and how to use them—gives you an edge.

Combine that technical know-how with the right tools and effective sales techniques, and you’ll stand out as a top-tier HVAC-R professional.

ServiceTitan is a tool you can try out if you want to present your refrigeration business in the most professional digital way possible. Book a demo to learn how to get started with ServiceTitan.

ServiceTitan is the all-in-one software that helps home service businesses manage field reporting and calculations, while improving customer service and boosting revenue.