Design Strategies

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Heat pump

1. Introduction
Heat pumps offer the most energy-efficient way to provide heating and cooling in many applications, as they can use renewable heat sources in our surroundings. Even at temperatures we consider to be cold, air, ground and water contain useful heat that’s continuously replenished by the sun. By applying a little more energy, a heat pump can raise the temperature of this heat energy to the level needed. Similarly, heat pumps can also use waste heat sources, such as from industrial processes, cooling equipment or ventilation air extracted from buildings.

2. How does it work?
A heat pump extracts heat from a low temperature source (air, water, ground), increases heat to a higher temperature and releases it where it is required for space and water heating. Heat pumps can also be operated in a reverse mode for cooling purposes. The heat pumping cycle can be divided in three steps:
Step 1.
A fluid with a boiling point lower than the heat source temperature serves as a medium for heat transport. It is called the working fluid or refrigerant. As the working fluid extracts the heat from the source through a heat exchanger, its temperature rises and it evaporates.
Step 2.
Then a compressor compresses the evaporated fluid. Consequently, the pressure and the temperature of the vapour increase.

Step 3.
Finally, heat is being transferred from the evaporated fluid to the heat distribution fluid (water or air) in the condenser. As it releases its heat, the working fluid temperature decreases to such a degree that it condenses. After passing through the expansion valve, the fluid regains its initial liquid, low-temperature and low-pressure state. It then flows back to the evaporator where the process starts all over again.

HEAT PUMP-v3-E (3)-1

 

The coefficient of performance (COP) of heat pump measures the amount of heat energy moved (in watts), divided by the electric energy used to move it (also in watts), at a given outdoor temperature. Higher COP values indicate a more efficient system. An electric resistance heater generating heat at 100% efficiency will have COP = 1, while a heat pump in heating mode ranges from a COP of 2 to 5, and a heat pump in cooling mode ranges from 2 to even 3.

3. Benefits

  • A heat pump produces between 3 – 5 times the amount of energy than the electricity required to power the unit.(2)(2)
  • Massive savings in hot water related expenses over the long term
  • It’s an environmentally friendly hot water option because it gives a reduction in greenhouse gas emissions through less energy requirements.
  • No roof space or panels needed
  • Can easily be combined with an existing water heater (solar, oil boilers)/li>

 4. Applications
Heat pumps are particularly suited for buildings with a high demand for space heating and sanitary hot water production, extensive work-intimes and a simultaneous need for cooling. In large buildings, several individual heat pumps can be placed in differentzones and each can be sized to meetthe needs of the space it conditions. Some zones of the building may needheating at the same time as other zones need cooling. When properly integrated, aheat pump system can recover excess heatin one zone (sunny side, computer rooms, etc.) andtransfer it via a water pipe loop to areas of the building requiring heating. It is therefore possible toachieve a balance between heating and cooling needs during a good part of the year (40 to 60%). When the demand for heat exceeds the energy reclaimed, a central heat pump can supply the distribution loop with heat from a renewable source, generally the ground. In reverse, the same heat pumpcan extract excess heat from the loop and dispose of it in the ground to replenish the heat source forfurther demand.

References
(1) http://sustainabilityworkshop.autodesk.com/buildings/heat-pumps
(2) http://www.seai.ie/Archive1/Files_Misc/TechnicalHPfactsheetforWeb.pdf
(3)http://www.energymatters.com.au/renewable-energy/solar-power/solar-hot-water/solar-heat-pumps.php
(4)http://www.heatpumpcentre.org/en/aboutheatpumps/howheatpumpsachieveenergysavings/Sidor/default.aspx

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