Absorption Heat Pump Systems Explained

Absorption heat pump systems use a refrigerant that changes state from liquid to gas as it absorbs heat from a low-temperature source.

This process is reversible, meaning the system can also release heat to a higher temperature destination, making it a highly efficient way to transfer heat.

The system consists of a generator, a condenser, an evaporator, and an absorber, which work together to facilitate this heat transfer.

These components are typically connected in a loop, allowing the refrigerant to flow through each one in a continuous cycle.

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An absorption heat pump system consists of several main units, including the generator, condenser, evaporator, absorber, and heat exchanger, as well as the suction device and shielding pump.

The simplest case requires five heat exchangers, one at each component and an internal heat exchanger. Solution heat exchangers, valves, and other auxiliary parts are also necessary components.

The absorber, generator, and pump can be regarded as a "thermal compressor", with the absorber equivalent to the inlet side of the compressor and the generator equivalent to the outlet side.

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The absorber can be seen as a carrier liquid that transports the generated refrigerant gas from the low-pressure side of the cycle to the high-pressure side.

The absorption heat pump can be used in three modes: heat pump, cooler, and heat transformer mode. This is due to the fact that the main components of devices that achieve these three purposes are the same.

The performance of the absorption heat pump is indicated by the coefficient of performance (COP), which is the ratio of the removed or provided heat to the energy input.

The COP for cooling performance is 0.8 to 1.6, while the COP for heating performance is 1.2 to 2.5. The temperature rise ΔT is generally 30–50 °C.

The maximum temperature of the absorption heat pump's output does not exceed 150 °C.

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There are different types of absorption heat pumps, each with its own unique characteristics. Type 2 absorption heat pumps, also known as heat transformers, are a notable example.

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In type 2 AHP, the condenser temperature is lower than the evaporator temperature. This type of absorption heat pump can output high-temperature heat medium, such as hot water steam, 25–50 degrees Celsius higher than the medium temperature waste heat it uses.

The type 2 absorption heat pump is a clever way to utilize low-grade waste heat, making it a great option for industries like petrochemical and coal chemical industries. It can achieve energy saving and emission reduction, and even reduce production costs.

There are two main types of absorption heat pumps.

Type 2 absorption heat pumps, also known as heat transformers, use waste heat to output high-temperature heat.

The condenser temperature is lower than the evaporator temperature in type 2 AHP.

This type of absorption heat pump can be driven by low-grade waste heat and achieves energy saving and emission reduction.

It has practical application in petrochemical and coal chemical industries.

The coefficient of performance of the second type absorption heat pump is generally between 0.4 to 0.5.

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Small Capacity Gas-Driven Absorption Heat Pumps are a type of heat pump that can be particularly useful for small-scale heating applications.

They have a compact design, with a rated power of 8 kW, making them a great option for smaller spaces or homes.

The prototype of a small capacity gas-driven absorption heat pump developed at the Department of Energy of Politecnico di Milano uses a relatively recent development in the manufacturing process of plate heat exchangers (PHE), the fusion-bonding technology, which allows for seamless assembly of 100% stainless steel PHEs.

This technology enables the compact design of the heat pump, allowing for reduced dimensions and cost without compromising efficiency.

The compactness of the heat pump is also due to the special design of the generator and the solution pump, which are new developments.

The prototype has been tested in an accredited laboratory in compliance with standard EN 12309-6:2014, and the results show a high Seasonal Gas Utilization Efficiency (SGUE) of 1.58.

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Here are the test conditions used to measure the Gas Utilization Efficiency (GUE) of the prototype:

This shows that the heat pump can operate efficiently at a range of loads and ambient conditions, making it a versatile option for heating applications.

Working fluids are a crucial part of the absorption heat pump system.

A mixture of fluid is used as the working fluid, which undergoes a cyclic change in temperature and concentration.

The concentration of the working fluid changes with temperature, with high temperatures increasing the concentration of high-boiling components, also known as the absorbent.

The absorbent releases the refrigerant when the temperature rises, and this process is reversible, releasing heat when the refrigerant is mixed with the refrigerant in the absorber.

Several types of mixtures can be used in the absorption unit, but water/lithium bromide and ammonia/water are the common choices.

The choice of working fluid depends on the specific application and requirements of the system.

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Thermal energy sources are a crucial aspect of absorption heat pumps. They can come from various sources, including solar thermal, geothermal, and natural gas.

Solar thermal energy can be harnessed using innovative hot water solar thermal energy collectors, which can produce water above 88 °C (190 °F). This can be used to drive absorption refrigerators, making ice that can be stored and used as an "ice battery" for cooling when the sun is not shining.

Geothermal energy is another promising source, with the earth's shallow ground temperature and groundwater having wide application prospects in energy use. Using absorption heat pump technology, 65–90°C geothermal water can be used to produce 7–9°C refrigerant water for summer air conditioning.

Natural gas is also a common heat source, and absorption heat pumps can be powered by it. In fact, gas-fired absorption heat pumps are sometimes called gas-fired heat pumps, and they can provide consistent CO₂ savings compared to condensing boilers.

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In the EU, gas-driven absorption heat pumps have shown significant potential in reducing CO₂ emissions for space heating and domestic hot water production. According to a study, they can replace gas boilers while exploiting the existing gas networks and operating efficiently, even with a high-temperature heat distribution system (radiators) and if air sourced.

Here are some CO₂ savings figures for lightly renovated buildings in the EU, comparing gas-driven absorption heat pumps to other technologies:

Absorption heat pumps with natural gas as a heat source are commercially available, offering a maximum temperature of 70 °C.

The efficiency of these systems is quite impressive, with an efficiency of approximately 150%. This means that the addition of 1 kWh of natural gas results in the production of 1.5 kWh of heat.

Adsorption heat pumps, on the other hand, use solid-sorption instead of liquid-sorption, making them a viable alternative.

The materials used in adsorption heat pump systems include silica gel – H2O, zeolite – H2O, active carbon – MeOH, and active carbon/salt - NH3.

These materials are regularly applied in adsorption heat pump systems, particularly in small heat pump systems with capacities ranging from 70-500 kW, which are mainly used for cooling.

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Black Hills Energy in Colorado is offering a major subsidy for gas-fired absorption heat pumps. This subsidy can help make these efficient systems more affordable for homeowners.

FortisBC in British Columbia has launched a rebate to save customers money on gas absorption heat pumps. The rebate can be a significant cost savings for those looking to upgrade their heating systems.

Colorado is offering some great incentives for energy-efficient upgrades. Black Hills Energy, a US-based energy provider, is providing a major subsidy for gas-fired absorption heat pumps.

If you're a Colorado resident, you can take advantage of this rebate by installing a gas absorption heat pump. These systems are eligible for the subsidy.

Residents of Colorado can get significant savings on their energy bills with gas absorption heat pumps. This type of heat pump uses a gas-fired compressor to extract heat from the air, making it a highly efficient option.

Black Hills Energy's subsidy for gas absorption heat pumps is a great opportunity for Colorado residents to reduce their energy costs.

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In British Columbia, FortisBC has launched a rebate for gas absorption heat pumps. This incentive aims to help homeowners save money on their energy bills.

The rebate is designed to encourage the adoption of more energy-efficient heating systems. By installing a gas absorption heat pump, homeowners can reduce their energy consumption and lower their greenhouse gas emissions.

FortisBC is a Canadian-owned company based in British Columbia. Their goal is to provide a rebate to help offset the upfront costs of purchasing and installing a gas absorption heat pump.

Homeowners who install a gas absorption heat pump may be eligible for a rebate from FortisBC. The rebate amount is not specified in the article, but it's worth inquiring about if you're interested in taking advantage of this incentive.

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The absorption heat pump industry is still in its early stages, with only one major manufacturer of ammonia-water heat pumps on the market, which has successfully installed thousands of units in the commercial sector.

Currently, the market for absorption heat pumps lacks the scale needed to boost industrialization and resulting cost reduction.

Reliability is a major concern for the widespread adoption of absorption heat pumps in the residential heating sector, requiring the ammonia sealed circuit to operate with no maintenance for thousands of hours per year, for at least ten years.

The use of ammonia as a refrigerant poses a challenge to industrialization, as it requires steel components and is not compatible with most copper alloy products.

To achieve significant market penetration, absorption heat pumps need to become safe, compact, and cost-effective products, making air-source, ammonia-water, absorption heat pumps a viable option.

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The developed prototype of the Gas-driven Absorption Heat Pump (GdAHP) can be partialized down to 15% of its rated power, 8 kW, without compromising performance.

This is made possible by the use of variable valves, which allow the system to tune its operation to a wide range of thermal loads and ambient conditions.

Table 2 shows the test conditions for measuring the Gas Utilization Efficiency (GUE) for high temperature application and average climate.

These test conditions demonstrate the system's ability to operate efficiently under different thermal loads and ambient conditions.

The Gas-driven Absorption Heat Pump (GdAHP) is a viable alternative heating technology that can contribute to decarbonizing the building sector.

In the EU average and warm climate, and in lightly renovated buildings, GdAHPs can provide consistent CO₂ savings compared to condensing boilers.

GdAHPs can even compete with full electrical and hybrid heat pumps in these conditions.

However, more efforts are needed to make GdAHPs safe, compact, and cost-effective products that can occupy consistent market shares.

The prototype under development presents some promising features that make GdAHPs viable for large-scale deployment in residential buildings.

Its dimensions are comparable to a standard domestic condensing boiler, measuring 500 mm wide, 400 mm deep, and 850 mm high.

The ammonia charge is well below 2 kg, making it a safer option.

Its experimental performances are quite promising, with a calculated Secondary Glucose Utilization Efficiency (SGUE) of 1.58.

This is thanks to the use of variable valves that allow for optimized operation over a wide range of thermal loads and ambient conditions.

This efficient design and compact size make the GdAHP a more attractive option for widespread adoption.