A heat pump moves thermal energy from one place to another using electricity. In heating mode it collects heat from outdoor air, the ground or water and delivers it indoors. In cooling mode a reversible system can move heat in the opposite direction.
The practical distinction is between heat moved and electricity consumed. A heat pump may deliver several units of heat for each unit of electricity under suitable conditions, but performance changes with temperature, installation and equipment design.
Quick summary: an evaporator absorbs heat; a compressor raises refrigerant pressure; a condenser releases heat; an expansion device lowers pressure; and some systems reverse the cycle.
The refrigeration cycle
Refrigerant absorbs heat in a low-pressure evaporator. A compressor raises its pressure and temperature, allowing it to release heat through a condenser. An expansion device lowers pressure before the cycle repeats.
This is the same physical principle used by many refrigerators and air conditioners. Heat is transferred rather than created from nothing.
How cold air still contains heat
Outdoor air can supply thermal energy even when it feels cold. The refrigerant and heat exchanger operate under conditions that allow heat to move from the air into the system.
As outdoor temperature falls, heating capacity and efficiency may decline. Equipment designed for the relevant climate is essential.
Coefficient of performance
COP compares useful heating or cooling output with electrical input under specified conditions. A heating COP of 3 means three units of heat delivered per unit of electrical input at that operating point.
COP varies over time. Seasonal efficiency and the real building load are more useful than a single laboratory figure for predicting bills.
Heat pump versus resistance heater
An electric resistance heater converts electricity into heat. A heat pump uses electricity to transfer additional heat from a source, which can make it more efficient for space heating.
Installation cost, climate, maintenance and distribution equipment still matter. Greater operating efficiency does not guarantee the lowest total cost.
Reversible heating and cooling
A reversing valve can change refrigerant flow so that the indoor and outdoor coils exchange roles. The same system can then heat or cool when designed to do so.
Not every air conditioner supports heating. Check the model specification rather than assuming that shared components imply identical features.
Air-source and ground-source
Air-source systems exchange heat with outside air. Ground-source systems exchange heat with the ground through engineered loops. Water-source systems use an appropriate water circuit.
Site conditions, space, installation cost and maintenance vary. A ground-source system is not automatically suitable for a small urban property.
Frost and defrost
In cold humid weather, frost may develop on an outdoor heat exchanger in heating mode. Some systems temporarily defrost it to maintain performance.
Normal defrost cycles differ from persistent ice caused by a fault. Follow manufacturer instructions if heating performance becomes abnormal.
Heat-pump water heaters
A heat-pump water heater transfers heat from surrounding air into stored water. It uses a compressor and heat exchangers rather than relying solely on electric resistance.
The equipment needs suitable airflow, drainage and installation space. Cooling of surrounding air can be helpful or undesirable depending on location.
Calculating electricity use
If a system delivers 12 kWh of heat at an average COP of 3, the illustrative electricity input is about 4 kWh. Real input also depends on fans, pumps and auxiliary equipment.
The bill depends on the applicable tariff and operating conditions. Do not confuse useful heat output with electrical energy consumed.
Why correct sizing matters
Heating and cooling capacity should match the building load. Airflow, insulation, controls and installation quality affect efficiency.
Oversized or undersized equipment can waste energy or provide poor comfort. Ask a qualified installer for a load assessment and realistic seasonal estimate.
Common faults
Weak heating may arise from restricted airflow, unsuitable settings, extreme weather or a technical fault. Unusual noise, leaks and repeated power trips require inspection.
Homeowners can check accessible filters and thermostat settings according to the manual. Refrigerant and electrical repairs require qualified technicians.
Heat pumps in Singapore
Singapore has relatively little demand for space heating. Heat-pump technology may be relevant to water heating and cooling, but the financial case depends on the actual application.
Compare hot-water use, installation space, electricity prices and servicing needs rather than importing assumptions from a cold-climate household.
Frequently asked questions
Can heat pumps work in cold weather? Yes, within their rated range, but performance varies. Is a heat pump the same as an air conditioner? They share a refrigeration principle, but functions differ.
Does COP greater than one violate conservation of energy? No, because heat is moved from another source. Do heat pumps need servicing? Yes, according to manufacturer guidance.
The mental model
Follow the path: source heat → refrigerant → compressor → destination heat. Then ask how much electricity is needed for the temperature difference.
A useful comparison considers installed cost, climate, seasonal performance and maintenance rather than a single advertised efficiency number.