The sensible heat calculator determines the heat required to change an object's temperature. This change in heat can make a body either cool down or heat up, depending on whether heat is removed from or added to the system. We rely on sensible heat to warm water for hot showers in winter and to chill drinks in the refrigerator during hot summer. Sensible heat is a function of the temperature change, the specific heat, and the mass of the object.
Sensible heat is also a useful concept in solar-energy-based technologies, especially in regions where solar power is irregular or seasonal. Sensible heat storage is a kind of solar thermal storage solution in which you store heat in a fluid medium such as water or oil, or a solid storage medium such as rocks, metals, or fabrics. It is the simplest form of heat storage and can be achieved with just a water storage tank and a heat source that drives the exchange of heat.
So, what is sensible heat? Read on to understand the concept of sensible heat and the sensible heat equation.
What is sensible heat?
When you heat or cool an object, a temperature change occurs; the heat responsible for that temperature change is the sensible heat. For instance, when you heat an ice cube, its temperature increases up to the point where it starts melting — that is, 0 °C. Similarly, as we heat water from room temperature, its temperature rises until it starts boiling. This heat that results in a temperature change is sensible heat. In other words, it is the heat that you can feel or sense.
In contrast, a heat component that only causes a phase change (such as ice melting into water, or water boiling into steam) is called latent heat. During a phase change, the temperature stays constant even though heat is being added or removed.
Sensible heat formula
Now that you know the definition of sensible heat, let's look at the sensible heat formula. The sensible heat is a function of the temperature difference, the material's specific heat, and the object's mass. The equation for sensible heat is:
Q = m · cp · (Tf − Ti)
where:
- Q — the sensible heat;
- m — the mass of the object;
- cp — the specific heat capacity;
- Ti — the initial temperature; and
- Tf — the final temperature.
A positive Q means heat is added to the object (it heats up), while a negative Q means heat is removed from it (it cools down).
How to calculate sensible heat
To calculate sensible heat:
- Enter the mass of the object.
- Fill in the specific heat capacity of the object (or pick a material from the list).
- Insert the initial temperature of the system.
- Enter the final temperature of the system.
- The calculator returns the value of the sensible heat.
Optionally, you can enter an energy price (per kWh) and a currency to estimate how much it would cost to supply (or remove) that amount of heat — handy for sizing water heaters, thermal stores, or HVAC systems.
Specific heat capacity
You can use the material list to directly fill in the value of the specific heat capacity. The most common values (in metric units, J/(kg·K)) are listed below; the calculator automatically converts them to American units, BTU/(lb·°F), when you switch the measurement system.
| Material | cp — J/(kg·K) | cp — BTU/(lb·°F) |
|---|---|---|
| Water | 4186 | 1.000 |
| Ice (0 °C) | 2090 | 0.499 |
| Air | 1005 | 0.240 |
| Aluminum | 897 | 0.214 |
| Steel | 490 | 0.117 |
| Iron | 449 | 0.107 |
| Copper | 385 | 0.092 |
| Glass | 840 | 0.201 |
| Concrete | 880 | 0.210 |
| Wood | 1700 | 0.406 |
Example: using the sensible heat calculator
Suppose you want to heat 1 kg of water from a room temperature of 20 °C to 80 °C for a hot drink. With the specific heat of water, cp = 4186 J/(kg·K):
Q = 1 × 4186 × (80 − 20) = 251,160 J ≈ 251.16 kJ ≈ 0.070 kWh
That is roughly 60 kcal of energy. If electricity costs 0.15 $/kWh, heating that water would cost about $0.01 in energy.
Units and measurement systems
This calculator supports both measurement systems. In the metric (SI) system you enter mass in kilograms, specific heat in J/(kg·K), and temperatures in °C, and the heat comes out in joules. In the American (Imperial) system you enter mass in pounds, specific heat in BTU/(lb·°F), and temperatures in °F, and the heat comes out in BTU. The result is always shown converted into joules, kilojoules, kilowatt-hours, kilocalories, and BTU at the same time.
FAQs
What is the difference between sensible heat and latent heat?
Sensible heat changes the temperature of a substance without changing its phase, so you can feel (sense) the difference. Latent heat is the heat absorbed or released during a phase change — for example, melting or boiling — while the temperature stays constant.
Can the sensible heat be negative?
Yes. If the final temperature is lower than the initial temperature, the temperature difference is negative, so Q is negative. A negative Q simply means heat was removed from the object as it cooled down.
What is specific heat capacity?
The specific heat capacity (cp) is the amount of heat needed to raise the temperature of 1 kg (or 1 lb) of a substance by one degree. Water has a very high specific heat (4186 J/(kg·K)), which is why it is such an effective heat storage medium.
Why is sensible heat important for solar energy storage?
In sensible heat storage, surplus solar energy is stored by raising the temperature of a medium such as water, oil, or rock, and later recovered as the medium cools. Because it only requires a storage tank and a heat source, it is the simplest and most widely used form of thermal energy storage.