Question 7 - Heat Pump Flashcards
Q7A) Describe the operation of a heat pump
The operation of a heat pump involves the transfer of heat from one location to another by using a refrigeration cycle. The basic components of a heat pump system include a compressor, condenser, expansion valve, and evaporator. Here’s a step-by-step overview of how a heat pump works:
Absorption of Heat:
In heating mode, the heat pump absorbs heat from an external source, such as outdoor air (air-source heat pump), the ground (ground-source heat pump), or water.
Compression:
The absorbed heat is then transferred to a refrigerant circulating in the system.
The compressor increases the pressure and temperature of the refrigerant, turning it into a high-temperature, high-pressure gas.
Condensation:
The hot, pressurized refrigerant is then condensed in the condenser coil, releasing heat to the indoor space. As it releases heat, it converts back into a liquid
Expansion Valve:
The refrigerant, now in a high-pressure liquid state, passes through an expansion valve.
As it expands, the refrigerant’s pressure and temperature drop.
Evaporation:
The low-pressure liquid refrigerant then enters the evaporator coil, where it absorbs more heat from the external source (heating mode)
This absorption causes the refrigerant to evaporate and turn back into a low-pressure gas.
Repeating the Cycle:
The cycle repeats as the refrigerant continues to circulate, absorbing and releasing heat to maintain the desired temperature in the space.
Q7B) What are the advantages and disadvantages of heat pumps
Advantages:
Energy Efficiency: Heat pumps are generally more energy-efficient compared to traditional heating and cooling systems, as they transfer heat rather than generate it. This can result in lower energy consumption and reduced utility bills.
Dual-Functionality: Heat pumps can provide both heating and cooling, offering a year-round solution for maintaining comfortable indoor temperatures.
Environmental Benefits: Heat pumps produce fewer greenhouse gas emissions compared to systems that rely on combustion for heating. This environmental advantage is more pronounced when the electricity used to power the heat pump comes from renewable sources.
Safety: Heat pumps operate without burning fuel, which eliminates the risk of carbon monoxide poisoning or other safety concerns associated with combustion-based heating systems.
Long Lifespan: With proper maintenance, heat pumps can have a relatively long lifespan, often exceeding 15 years.
Consistent Temperature Control: Heat pumps provide more consistent and even heating compared to some traditional heating systems.
Disadvantages:
Upfront Cost: The initial cost of purchasing and installing a heat pump can be higher than that of traditional heating and cooling systems. However, long-term energy savings may offset this cost difference.
Climate Dependency: Air-source heat pumps may experience reduced efficiency in extremely cold climates, as there is less heat available in the outdoor air. In such cases, supplemental heating may be needed.
Installation Challenges: Ground-source heat pumps (geothermal) can be more complex and costly to install, requiring specific geological conditions and expertise.
Maintenance Requirements: Heat pumps require regular maintenance to ensure optimal performance. The coils, filters, and other components need to be cleaned or replaced periodically.
Noise: Some heat pumps, especially older models or those with inadequate sound insulation, may produce noise during operation. However, newer models are designed to be quieter.
Space Considerations: The installation of certain types of heat pumps, such as ground-source systems, may require significant space for the outdoor components, such as the ground loop.
Q7C) Size a ground source heat coil (horizontal loop)
Pipes need to be installed at least 1m apart and 1.5 metres down into the ground. Pipes cannot just be directly 400 m, it can separated into different lengths
- Calculation
Area Required =
System Size kW / NI Soil Conductivity
6kW / 20 Wm-2 = 300 m2
Depending on the spacing between each pipe, typical around 0.7-1.2 m per pipe.
Area / pipe space
300 / 0.8 = 375m
Round up to 400m in 4 x 100m Lengths
