Energy Efficiency is a very important factor these days, which drives our aim to become a Global, Leading Green Company.

The Mitsubishi Electric Group established Environmental Vision 2021 to contribute to the development of a sustainable society, and is advancing initiatives to achieve a low-carbon, recycling-based society. While this vision represents the company, we aim to become by the 100th anniversary of our founding in 2021, our ultimate goal is to make lasting social contributions as a leading green company.

To this end, we are working to strengthen our corporate constitution and to contribute to society. Strengthening our corporate constitution refers to disciplining ourselves to use less energy and fewer resources in our manufacturing, and increasing production efficiency to the highest level possible. Specifically, this means reducing waste generated during production and thoroughly implementing the “3Rs” of resources: reduce, reuse and recycle.

Mitsubishi Electric products are made with a vision of “Eco Changes for a greener tomorrow,” which is our commitment to the society to develop energy efficient products.

A winning combination for HVAC

With the advance of technology, Variable Refrigerant Flow (VRF) type air conditioners are now capable of transferring the heat energy from inside the room to hot water. VRF is an air-condition system configuration where there is one outdoor condensing unit and multiple indoor units. The arrangement provides an individualised comfort control, and simultaneous heating and cooling in different zones.

Most leading brands in air conditioners like Mitsubishi Electric have introduced two-pipe or three-pipe VRF systems that provide simultaneous heating and cooling.

Two-pipe system with simultaneous heating and cooling operations

Heat recovery type VRF systems are normally available in water cooled and air cooled systems. In water cooled type systems, a double heat recovery is possible. The refrigerant from the condenser and indoor units (which are a mix of vapour and liquid) is passed through a set of valves, which separates the gas and liquid and diverts the flow of refrigerant to required indoor units, depending upon the heating or cooling requirement. These types of VRF units can have special type of indoor units known as air to water type. They have refrigerant and water passing through a plate type heat exchanger and depending upon the temperature settings on the water side part of indoor, the valve assembly diverts the refrigerant for heating or cooling of water.

Cooling main with hot water generation…

50% Cooling with 50% hot water Generation.
( Most energy efficient operation)…

Schematic diagram of Booster unit…

What helps is that a maximum amount of energy efficiency is obtained after water is heated when the other indoor units are in cooling operation. It also means that a simultaneous generation of hot water and heating by indoor units is possible during the operation. While air cooled outdoor units will expel unutilised energy into the atmosphere, water cooled units can be used for double heat recovery – expelling the energy to water which can then be used for pre-heating the water for other applications.

A schematic diagram of typical heat recovery system with hot water generation has been mentioned above.

Features of the system

The system provides two types of air to water indoor units. The first one is the Auxiliary unit which recovers available heat from air conditioning operation with a maximum water temperature up to 40° Celsius. The second one which is the Booster unit contains an additional inverter driven compressor which can generate water up to 70°Celsius.

The number of air to water indoor units have to be selected depending upon the hot water requirement. The capacity of the auxiliary unit is available with 12kW and 25 kW heating capacity with a maximum temperature output up to 40°Celsius.The capacity of Booster unit is 12 kW with a maximum outlet temperature up to 70°Celsius. The maximum connectivity of air to water type indoor units are 50 to 150 per cent when connected with standard indoor units. Outdoor capacity is available from 08 HP to 36 HP capacity in air cooled type.

The selection of the capacity of air to water indoor units is calculated on the basis of a formula like this:

Capacity of Air to water indoor (in kW) = {(T2-T1) x 1 Kcal/Deg hour x Water qty in Liters} / 860.

(Adding a safety factory of 15 per cent to the derived kW from above calculation is important) T2 – water outlet temp, T1- water inlet temperature.

The maximum water flow rate for the Air to Water series is 0.6 m3 / hr to 2.15 m3 / hr, the operating pressure is 1 Mpa and the output temperature for water is 10° to 40°Celsius (70°Celsius for Booster type units).

A technological marvel

While understanding the features is easier, some questions still remain unanswered. An often-asked question is: can we get hot water even if the air conditioner is not operating? The answer to this is an emphatic yes! Hot water is generated irrespective of the operation of the other indoor units. However, the best efficiency is when other indoor units with a capacity equal to the air to water type indoor units are operating in cooling mode. (50% cooling, 50% for heating water).

Since the air to water type indoor units are multi-pass storage type, increase in temperature at a single pass is generally less than 5°Celsius. A storage tank with a closed loop system and multiple passage of water to increase the temperature is needed.

Many people wonder whether such a system can be used along with a solar type-water heater. Air to water type indoor units can be used to increase the feed water temperature to solar water heaters and can also be used to maintain the temperature of the water at a desired level during the night or in low sunlight periods. This applies mainly to the hotel industry where the requirement of hot water is high during early morning hours.

The recommended water quality standard is  JRA-GL02E  or equivalent…

System for India?

One may also wonder if this type of system is suitable for the water quality that is available in India. While using the system in India, it is mandatory to use a closed loop system with the storage tank and air to water type indoor units. This helps in maintaining the efficiency of the system, and also prevents scaling inside the air to water type indoor units. Periodically PHE (Plate Type Heat Exchanger) inside the storage tank can be replaced. It is advisable to use de-mineralised water between the PHEs.


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