Heat Pump

A heat pump is a device that provides heat energy from a source of heat to a destination called a ‘heat sink.’ Heat pumps are designed to move thermal energy opposite to the direction of spontaneous heat flow by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses some amount of external power to accomplish the work of transferring energy from the heat source to the heat sink.

Principle of working of a heat pump

While air conditioners and freezers are familiar examples of heat pumps, the term ‘heat pump’ is more general and applies to many HVAC (Heating, Ventilating, and Air Conditioning) devices used for space heating or space cooling. When a heat pump is used for heating, it employs the same basic refrigeration type cycle used by an air conditioner or a refrigerator, but in the opposite direction releasing heat into the conditioned space rather than the surrounding environment. In this use, heat pumps generally draw heat from the cooler external air or from the ground. In heating mode, heat pumps are three to four times more efficient in their use of electric power than simple electrical resistance heaters.

In Heating, Ventilation and Air Conditioning (HVAC) applications, the term heat pump usually refers to easily reversible vapour compression refrigeration devices optimised for high efficiency in both directions of thermal energy transfer. Heat spontaneously flows from warmer places to colder spaces. A heat pump can absorb heat from a cold space and release it to a warmer one. Heat is not conserved in this process, which requires some amount of external high grade (low entropy) energy, such as electricity.

Most of the energy for heating comes from the external environment, and only a fraction comes from electricity (or some other high grade energy source required for running a compressor). In electrically powered heat pumps, the heat transferred can be three or four times larger than the electrical power consumed, giving the system a Coefficient of Performance (COP) of 3 or 4, as opposed to a COP of 1 for a conventional electrical resistance heater, in which all heat is produced from input electrical energy.

Air source heat pump (extracts heat from outside air)

• Air–air heat pump (transfers heat to inside air)
• Air–water heat pump (transfers heat to a heating circuit and a tank of domestic hot water)
• Water to water heat pump
• Reversible heat pump

Applications in industry

• Hospitals
• Hotels
• Canteens
• Hostels religious centers
• Residential
• Retail outlets

Heating of water for canteen application

There are two fold applications for water heating, which is done by PNG and Electrical Storage Geysers.
Cooking: wherein there are large Pot-Boilers wherein the water is boiled by means of Piped Natural Gas (PNG). (Temp. requirement for Cooking @ 80-100°C)

Washing and cleaning:

i. Soiled dishes are washed in automatic dish washing machine wherein hot water is required at temp @ 50°C. Hot water    is obtained from storage geysers.
ii. Soiled vessels are washed manually, wherein storage geysers are used for hot water application.

Alternative means of heating was explored viz. solar hot water system, which is purely renewal and clean energy. However, on a practical note, it was not viable. The reason being the ‘demand of hot water at a particular interval of time was phenomenal.’

To manage the demand one has to install solar system of very large generation and storage capacity, which requires large amount of footprint and also the investment. Maximum output of solar water heating system is available during 11AM to 4PM.

Heat pump seemed to be the most viable option, as it can operate 24 x 7. However, it uses electrical energy. Compared to electrical and PNG, a heat pump is much more efficient.

Heat pump details:

• Make : STG (RC Group)
• Model : SMART HP T-33
• Type : Air to hot water
• Capacity : 38.8 kW
• Max. Hot water leaving temp. : 50°C
• Water Entering Temp. : 10 to 40°C

Savings calculation:

• Savings in PNG energy cost: ` 4.8 Lacs
• Investment towards Heat Pump Project: ` 19 Lacs
• Payback period: 4 Yrs.