What is a heat pump?
When you think of a device to cool your house the first thing that comes to your head is an air conditioner. However, a heat pump is a machine that is used to both cool and heat a building. It takes heat from one source and transfers it to another location by electrical or mechanical means. It is an essential part of central heating cooling system that cools home in summer makes them warm in winter. It has an advantage over furnaces as it does not need fuel to generate heat. Therefore its running cost is lower and it is more eco-friendly.
How does a heat pump work?
A heat pump typically has two parts- an indoor unit called the air handler and an outdoor unit which is similar to central air conditioner. The functioning of a heat pump is quite simple. The device transfers heat by circulating low pressure gas called refrigerant through a cycle of evaporation and condensation. The unit has a compressor that pumps the refrigerant into two coils. In the first coil the refrigerant is evaporated by absorbing heat from the surrounding. The gaseous refrigerant then reaches the compressor. The compressor compresses it and sends it to the other coil. Here it is condensed at a high pressure to release heat. This heat is used to warm up rooms. The electric energy that is needed to power the compressor is also added to heat generated in the condenser. The efficiency of a heat pump is denoted by the ratio of total heat given by the heat pump to the amount of electricity needed to run it. It also called Coefficient of Performance (COP). This cycle in the heat pump can be reversed to cool rooms instead of heating them.
What are the different types of heat pumps on the basis of heat source?
Heat pumps can be differentiated on the basis of the source from where it draws heat:
Air-Water heat pumps:
These are very basic models of heat pump. It has two fans, refrigerator coils, a reversing valve and a compressor to make it work. The heat pump draws heat from the external air and transfers it to the source, which consists of a water circuit. This in turn heats rooms.
Air-Air heat pumps:
It is also very similar to the air-water model. Here it absorbs heat from the external air and transfers it to air ducts. The heat is transferred to your room though these ducts. Remember that there is a reversing valve in a heat pump. It is this valve which can reverse the flow of the refrigerant. So instead of pumping the heat inside your house, it releases the heat outside which leads to cooling it.
Ground Source:
They are a little different. They absorb heat from the lakes, river or underground and transfer it to a water circuitorto air ducts for heating the house. The heat is absorbed through underground pipes filled with water or refrigerant. These pipes can be open loop as well as closed loop. In closed loops the same water or refrigerants circulate in the pipe. But in open loop water is taken into the pipe and the heat is extracted from it. The water is then returned to its source. These are also called geothermal heat pumps.
What are the various commercial heat pumps?
Mechanical heat pump: The mechanical heat pump is the most commonly used and commercially feasible heat pump. There are two types
• DX Heat Pump:
This is called the Direct Expansion heat pump. Here the whole refrigerant volume at the opening of the expansion device is delivered in the evaporator. Alarge portion of therefrigerant evaporates due toexpansion. The refrigerant is mostly gaseousand partly liquid. It now enterstheevaporator. The liquid part of refrigerant evaporates in the evaporator. When most of the refrigerant isevaporated, it is slightly superheated andmoved to the compressor. Superheating is crucial here to prevent liquid slugging, which can damage the compressor. Once it reaches the compressor the regularcycle of aheat pump takes place to release heat.
• Pump system:
In this system liquid refrigerant is moved to the evaporator. Inside the evaporator the refrigerant is partly evaporated. The refrigerantwhich is amixture of gas and liquid now is sent to separator vessel. In the vessel the liquid and gaseousrefrigerant is separated. The gaseous part goes to the compressor to complete regular cycle of a heat pump. The liquid part goes to evaporator again.
The pump mechanism has an advantage. As you will only supply fluid refrigerant, a moderately-sized evaporator will do. But in these units you need an additional refrigerant pump and separation vessel. These pumps aremostly used in industrial sets ups.
Superheating ofthe refrigerant in dx systems leads to releaseof high temperatures. This can demolish the compressor oil.
Gas engine heat pump:
The gas engine heat pumps work in the same way as a mechanical heat pump. The only notable differenceisthat the heat pump is powered by a gas engine instead ofan electric motor. Here the heat from the motor cooling and flue gases is utilized as well. These heat pump systems have high heating output even with low outdoor air temperatures.They have higherenergy efficiency. You have lower running cost as you are not using electricity. It is eco-friendly as there will be less CO2 emissions.
These heat pumps are often used in restaurants, showrooms, shops, offices, hotels, schools, care-centers, sports clubs, factories and such other places.
Absorption heat pump:
It works in the same way as air-air heat pump. The only notable difference is that instead of using a refrigerant it uses Lithium-Bromideor ammonia in water. The driving force in this type of heat pump is thermal energy. Absorption heat pumps can be very useful where both heating and cooling are necessary. These are powered by natural gas, solar power, propane, or geothermal heated water.
In theseammonia (NH3) is used as refrigerant. It is evaporated into gas inan evaporator. Instead of sending it to a compressor, NH3 is absorbed in water. This leads to release of heat. Thenext step is removing ammonia from water. It is here that a heat source is needed. The source boils the liquid to evaporatethe ammonia out. The gaseous ammonia flows towards the condenser. Inside the condenser the NH3 releases heat to its environments and condensate. The pressure of liquid Ammonia is further lowered in an expansion device. It goes towards the evaporator to start the cycle once again. A key part of these heat pumps is generator absorber heat exchanger technology, or GAX. This collects and uses the heat that is released when ammonia is absorbed in water. These days you will get these heat pumps withhigh-efficiency vapor separation, variable ammonia flow rates, and low-emissions, variable-capacity combustion of the natural gas.
Adsorption heat pump:
It just works like an absorption heat pump. The only difference is that it uses a solid instead of a fluid as absorption medium. Here is a list of combinations that work in adsorption heat pumps
• Silica gel – H2O
• Zeolite – H2O
• Active carbon – MeOH
• Active carbon/salt - NH3
Transcritical CO2 heat pump:
This is in contrast with regular compressor systems where heat release takes place at a fixed temperature. Here heat release takes place above the critical pressure of 71 Bars. The refrigerant cools down and not condensate as in other heat pumps. These heat pumps are more efficient. For higher heat output water at lowertemperature is needed.
Thermoacoustic heat pump:
This is based on the science principle that difference in temperature cangenerate sound waves. And in a reverse way a sound wave can generate a temperature difference. Here sound wave is generated with low temperature waste heat. This wave is used to create temperature difference in a high temperature medium. These heat pumps have not been built or utilized at a commercial scale yet.
Cost of buying and installing heat pump is a fat investment. Buying and installing a 3-ton heat pumps in a residence could start from $4500 and go up to $8000 and more. That gives you a fair idea what could be the cost of 20 to 50-ton heat pumps that will be needed in commercial sets ups.
Sections Coming:
• Hybrid Heat Pumps
• Maintenance cost of commercial Heat pumps
• Where to find installation and maintenance professions?
• Tax rebates for buying commercial Heat pumps
• Top Brands of Commercial Heat Pumps with distributors
What is an HVAC system?
Heating, Ventilating, and Air Conditioning (HVAC) equipment arewidelyusedtoday to cool or heat residential, commercial or industrial buildings, according to seasonal needs. These systems also play a key role in disinfecting your indoor air from aerial contaminants such as odors, volatile organic compounds producedby furnishings, chemicals used for cleaning, and dust mites, molds etc. A properly designed system will provide fresh and breathable air round the year. Here are some major types of
commercial HVAC system:
Variable Air Volume (VAV) :
These are single duct air system that can facilitate varying airflow. This is in keeping with varied cooling and heatingdemands in a building. There is an air handler blower fan which modulates to change the airflow. These have Variable Air Volumebox integrated in the system. There are airflow sensors inside these boxes which can measure the airflow. If the box is in cooling mode, then the damper will fully open to allow the flow of maximum air. High flow of air is needed during cooling. Heating requires minimum air flow so the handler will allow a low airflow.
Constant Air Volume (CAV):
The temperature of the air that is being sent to cool or heat rooms can be regulatedbased on outside air temperature. However, there is a constant supply air volume through the distribution system. These systems have reheat box that can control the temperature and humidity. In a big premise, the various parts will have different heating and cooling needs. In some zone the supply air should a little cooler and in some zones it should be a littlewarmer.Thecool air is sent in the ducts. In zone that needs warm air, it is heated these boxes and the circulated in the respective room throughducts. This system is called reheat system.
There is another mechanism called mixing system. In this there are twodistribution systems, one for cooling and the other for heating. These two ducts meet at the space and mix two types of air in a mixing box to bring it to needed temperature and thereafter send it to rooms.
Sections coming:
• Variable refrigerant
• Chilled beam
• Heat pump fan coil
• Unit Ventilators (UV)
• Displacement Ventilation
• Geothermal
• Hybrid geothermal