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Temperature is one of the most important measurements in HVAC and refrigeration systems. From maintaining a comfortable indoor environment to preserving pharmaceutical products, frozen foods and other temperature-sensitive goods, accurate temperature measurement and control are essential.
Temperature Unit Converter
HVAC technicians, refrigeration engineers, facility managers and cold-chain operators commonly encounter temperatures expressed in degrees Celsius (°C), degrees Fahrenheit (°F), and Kelvin (K). Other temperature scales also exist, but these three are particularly important when working with modern engineering, refrigeration and air-conditioning systems.
For example, a pharmaceutical cold room may operate at +2°C to +8°C, a freezer may operate at -18°C, while a comfortable air-conditioned indoor environment may be approximately 20°C to 24°C, depending on the application.
Understanding temperature units makes it easier to interpret equipment specifications, refrigeration setpoints, operating manuals, temperature controllers, technical drawings and international equipment documentation.
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Temperature is a physical quantity that indicates how hot or cold a substance, object or environment is.
In HVAC and refrigeration, temperature is used to monitor and control conditions such as:
Temperature itself is not the same thing as heat.
Heat is energy transferred because of a temperature difference, while temperature describes the thermal condition of a substance or environment.
This distinction is particularly important when studying refrigeration heat-load calculations and system performance.
The three temperature scales most relevant to HVAC and refrigeration engineering are:
Celsius and Fahrenheit are commonly used to communicate practical operating temperatures, while Kelvin is particularly important in scientific and engineering calculations involving absolute temperature.
The Celsius scale is one of the most widely used temperature scales in the world and is the principal temperature scale used in Nigeria and most countries using the metric system.
It is commonly used in HVAC and refrigeration applications to specify:
The Celsius scale is based on the freezing and boiling points of water at standard atmospheric pressure:
There are therefore 100 Celsius degrees between these two reference points.
| Application | Typical temperature example |
|---|---|
| Air-conditioned room | 20°C–24°C |
| Pharmaceutical cold storage | +2°C to +8°C |
| Chilled food storage | Approximately 0°C–5°C |
| General cold room | Approximately 0°C to +5°C |
| Frozen food storage | Around -18°C |
| Deep-freezing applications | Below -18°C |
| Ice production | Around 0°C or below, depending on the process |
Actual operating temperatures depend on the product, equipment design, process requirements and applicable standards.
The Fahrenheit scale is widely used in the United States and is encountered frequently when working with HVAC and refrigeration equipment manufactured for the North American market.
On the Fahrenheit scale:
Therefore, the difference between the freezing and boiling points of water is 180°F.
This means that one degree Fahrenheit represents a smaller temperature interval than one degree Celsius.
For example:
20°C = 68°F
and:
-18°C ≈ 0°F
This is why refrigeration equipment specifications originating from the United States may use Fahrenheit even when the same equipment is being operated elsewhere.
The Kelvin is the SI unit of thermodynamic temperature.
Unlike Celsius and Fahrenheit, Kelvin is an absolute temperature scale.
Kelvin does not use the degree symbol.
Correct:
273.15 K
Not:
273.15°K
The Kelvin scale begins at absolute zero, the theoretical lower limit of thermodynamic temperature.
Absolute zero is:
0 K = -273.15°C = -459.67°F
The size of one Kelvin is the same as the size of one Celsius degree.
Therefore:
1 K temperature difference = 1°C temperature difference
However, their zero points are different.
For example:
0°C = 273.15 K
25°C = 298.15 K
-18°C = 255.15 K
Kelvin is particularly useful in engineering calculations involving:
The three scales can describe the same physical temperature, but they use different numerical values.
| Temperature | Celsius | Fahrenheit | Kelvin |
|---|---|---|---|
| Absolute zero | -273.15°C | -459.67°F | 0 K |
| Water freezing point | 0°C | 32°F | 273.15 K |
| Comfortable room temperature | 20°C | 68°F | 293.15 K |
| Room temperature | 25°C | 77°F | 298.15 K |
| Water boiling point | 100°C | 212°F | 373.15 K |
| Typical frozen-food storage | -18°C | approximately 0°F | 255.15 K |
The numbers are different, but they describe the same thermal condition.
HVAC and refrigeration professionals may need to convert temperatures between Celsius, Fahrenheit and Kelvin.
The formula is:
°F = (°C × 9/5) + 32
Convert 5°C to Fahrenheit:
°F = (5 × 9/5) + 32
°F = 9 + 32
°F = 41°F
Therefore:
5°C = 41°F
The formula is:
°C = (°F – 32) × 5/9
Convert 41°F to Celsius:
°C = (41 – 32) × 5/9
°C = 9 × 5/9
°C = 5°C
Therefore:
41°F = 5°C
The formula is:
K = °C + 273.15
Convert -18°C to Kelvin:
K = -18 + 273.15
K = 255.15 K
Therefore:
-18°C = 255.15 K
The formula is:
°C = K – 273.15
Convert 293.15 K to Celsius:
°C = 293.15 – 273.15
°C = 20°C
Therefore:
293.15 K = 20°C
The formula is:
K = (°F – 32) × 5/9 + 273.15
Convert 32°F to Kelvin:
K = (32 – 32) × 5/9 + 273.15
K = 273.15 K
Therefore:
32°F = 273.15 K
The formula is:
°F = (K – 273.15) × 9/5 + 32
Convert 273.15 K to Fahrenheit:
°F = (273.15 – 273.15) × 9/5 + 32
°F = 32°F
Therefore:
273.15 K = 32°F
One of the most important concepts in HVAC and refrigeration is the difference between temperature and temperature difference.
A temperature tells us how hot or cold something is.
A temperature difference tells us how far apart two temperatures are.
For example:
Return air = 24°C
Supply air = 14°C
The temperature difference is:
24°C – 14°C = 10°C
Therefore, the air-conditioning system has a 10°C temperature difference between return and supply air.
When discussing a temperature difference, a difference of 10°C is equivalent in magnitude to 10 K.
However, this does not mean that 10°C and 10 K represent the same absolute temperature.
Temperature difference is commonly used when evaluating HVAC system performance.
For example:
AIR-CONDITIONING UNIT
RETURN AIR
24°C
│
▼
┌─────────────┐
│ HVAC │
│ UNIT │
└──────┬──────┘
│
▼
SUPPLY AIR
14°C
Temperature Difference:
24 - 14
= 10°C
The actual expected temperature difference depends on the equipment, system design, airflow, indoor conditions, load and operating conditions.
It should therefore not be assumed that every air-conditioning system must produce the same temperature difference.
ROOM
┌───────────────────────┐
│ │
│ 24°C │
│ RETURN AIR │
│ ↑ │
│ │ │
│ ┌───────┐ │
│ │ HVAC │ │
│ │ UNIT │ │
│ └───┬───┘ │
│ │ │
│ ↓ │
│ 14°C │
│ SUPPLY AIR │
│ │
└───────────────────────┘
ΔT = Return Air - Supply Air
ΔT = 24°C - 14°C = 10°C
Temperature measurement becomes even more important in refrigeration.
A refrigeration system can contain several different temperatures at the same time.
For example, a refrigeration system may have:
These temperatures are related to the operation of the refrigeration cycle but are not necessarily the same.
A cold room operating at -18°C, for example, does not mean that the refrigerant leaving the evaporator must also be at -18°C.
The refrigeration system requires a temperature difference between the refrigerated space and the evaporating refrigerant to transfer heat from the room into the refrigeration system.
This distinction is important when designing and troubleshooting cold rooms.
Consider a freezer operating at:
Room temperature = -18°C
The evaporating refrigerant temperature may be lower than the room temperature.
The exact evaporating temperature depends on factors including:
Therefore, the room temperature, evaporating temperature and refrigerant temperature should not be treated as interchangeable measurements.
Different refrigeration applications require different temperature ranges.
There is no single temperature that applies to all refrigeration systems.
| Application | Example temperature range |
|---|---|
| Comfort air conditioning | Approximately 20°C–24°C |
| Chilled storage | Approximately 0°C–5°C |
| Pharmaceutical cold storage | Commonly +2°C to +8°C |
| Frozen-food storage | Approximately -18°C |
| Deep-freezing | Below -18°C |
| Ice production | Around 0°C or below, depending on process |
| Blast freezing | Often below -30°C, depending on application |
| Ultra-low-temperature applications | Can be below -40°C |
These are general examples, not universal design requirements. The required temperature should always be determined by the product, process, applicable standards and equipment design.
| °C | °F | K |
|---|---|---|
| -40 | -40 | 233.15 |
| -30 | -22 | 243.15 |
| -20 | -4 | 253.15 |
| -18 | approximately 0 | 255.15 |
| -10 | 14 | 263.15 |
| 0 | 32 | 273.15 |
| 2 | 35.6 | 275.15 |
| 5 | 41 | 278.15 |
| 8 | 46.4 | 281.15 |
| 10 | 50 | 283.15 |
| 15 | 59 | 288.15 |
| 20 | 68 | 293.15 |
| 24 | 75.2 | 297.15 |
| 25 | 77 | 298.15 |
| 30 | 86 | 303.15 |
| 40 | 104 | 313.15 |
| 50 | 122 | 323.15 |
Values are rounded where appropriate.
Suppose a pharmaceutical cold room is designed to maintain:
+2°C to +8°C
The equivalent Fahrenheit range is approximately:
35.6°F to 46.4°F
The equivalent Kelvin range is:
275.15 K to 281.15 K
Suppose frozen products are stored at:
-18°C
This is approximately:
0°F
and:
255.15 K
Suppose an indoor environment is maintained at:
24°C
This corresponds to:
75.2°F
and:
297.15 K
Suppose:
Return air = 25°C
and:
Supply air = 15°C
Then:
ΔT = 25°C – 15°C
ΔT = 10°C
The temperature difference is therefore 10 K as a temperature interval.
A common misunderstanding in HVAC and refrigeration is to treat temperature as a measure of cooling capacity.
It is not.
Temperature tells us how hot or cold something is.
Cooling capacity describes the rate at which a refrigeration or air-conditioning system can remove heat.
Cooling capacity may be expressed in units such as:
For example, two air-conditioning systems can both maintain a room at 24°C while having completely different cooling capacities.
The required cooling capacity depends on factors such as:
Similarly, two cold rooms can both operate at -18°C but require different refrigeration capacities because of differences in size, product load, insulation, door openings, ambient conditions and operating requirements.
In cold-chain applications, maintaining the correct temperature is not simply about making a room cold.
The refrigeration system must maintain the required conditions throughout the intended operating period.
This can involve:
For solar-powered or off-grid refrigeration systems, temperature requirements also influence the sizing of the refrigeration equipment and the electrical/solar energy system.
Temperature is a fundamental measurement in both HVAC and refrigeration engineering.
The three most important temperature scales encountered in these fields are:
Celsius (°C), Fahrenheit (°F), and Kelvin (K).
Celsius is widely used for everyday HVAC and refrigeration applications, Fahrenheit remains common in the United States and some international equipment documentation, while Kelvin is the SI unit of thermodynamic temperature and is important in engineering calculations.
Understanding the difference between:
is essential for correctly interpreting HVAC and refrigeration systems.
Most importantly, the temperature displayed by a controller is only one part of understanding system performance. Proper system design requires consideration of cooling capacity, heat load, equipment selection, airflow, refrigerant conditions, insulation, controls and the specific requirements of the application.
Whether the application involves an air-conditioning system, cold room, freezer, pharmaceutical storage facility, blast freezer or other temperature-controlled environment, accurate temperature measurement is fundamental to reliable operation.
The main temperature units encountered in HVAC are degrees Celsius (°C), degrees Fahrenheit (°F), and Kelvin (K).
Celsius (°C) is commonly used in Nigeria for HVAC, refrigeration and engineering applications.
No. -18°C is approximately 0°F. Celsius and Fahrenheit use different scales.
No. 0°C = 273.15 K. Absolute zero is 0 K, which is -273.15°C.
Celsius and Kelvin have the same size temperature interval, but their zero points are different. 0°C = 273.15 K.
Kelvin is an absolute temperature scale and is used in thermodynamic and engineering calculations where absolute temperature is required.
Many frozen-food storage applications use approximately -18°C, although the required temperature depends on the product, process and applicable requirements.
A commonly encountered pharmaceutical storage range is +2°C to +8°C, but the required range must be determined from the specific product and applicable storage requirements.
Temperature differences are used to evaluate conditions such as supply-air versus return-air temperature and are also fundamental to heat transfer and refrigeration-cycle analysis.
Yes. The evaporating refrigerant temperature can be lower than the cold-room air temperature so that heat can be transferred from the room into the refrigeration system. The exact temperature depends on the system design and operating conditions.
Akpo Oyegwa Refrigeration Company (AORC) provides refrigeration, air-conditioning, cold-room and solar-powered refrigeration solutions for commercial, industrial and other temperature-controlled applications in Nigeria.
Our services include refrigeration system design and installation, cold rooms, freezers, HVAC/R systems, solar-powered cold storage solutions, solar-powered refrigeration systems, equipment supply, maintenance and related technical services.
For a temperature-controlled project, the correct temperature requirement is only the starting point. Proper equipment selection and system design require consideration of the required temperature, heat load, storage capacity, product characteristics, ambient conditions, operating schedule and power requirements.
Contact Akpo Oyegwa Refrigeration Company for professional refrigeration and HVAC solutions tailored to your project requirements.