Frequently Asked Questions
Adsorption Technology Basics
Adsorption refers to the accumulation of adsorbates such as gases or liquids on the surface of solid materials called adsorbents. This process is employed in adsorption cooling systems, which use working materials like alcohol/zeolite or water/silica gel to generate low temperatures. Adsorbents eventually become saturated over time, necessitating a regeneration process called desorption, during which the captured water vapor is released by heating.
The Boulton system utilizes water as the adsorbate, making it entirely emission-free, non-toxic, and ecologically safe. Various adsorbents are based on crystal structures of widespread elements like aluminum, silicon dioxide, and iron, along with environmentally friendly binders, representing a novel innovative technique. When combined with Boulton’s patented mechanical components, an astonishing thermal capacity can be achieved.
Silica gel is a harmless, eco-friendly substance known for its exceptional adsorption capabilities, making it a popular choice for various applications, including dehumidification and adsorption cooling technology. Its wide working temperature range makes it a versatile adsorbent suitable for diverse purposes. Due to its high thermal stability and low cost, silica gel is widely used as an adsorbent. Its excellent moisture-absorbing performance has earned it a reputation as an effective desiccant in various sectors. In adsorption heat technology, silica gel is renowned for its ability to work over an extensive temperature range, making it a reliable and flexible choice for diverse heating and cooling applications.
Zeolites are a group of natural or synthetic minerals with a porous structure that makes them efficient adsorbents and catalysts. They consist of frameworks formed by aluminum, silicon, and oxygen atoms, which create regular, interconnected pores and channels with uniform sizes and shapes. The unique structure of zeolites allows them to selectively adsorb molecules based on size, shape, and polarity, making them suitable for various applications, including gas separation, water purification, and catalysis. Zeolites are also known for their high thermal stability and resistance to chemical corrosion, making them an ideal choice for use in harsh environments. They can be synthesized in various shapes and sizes and can be customized by modifying their structure or adding functional groups to their surfaces. Zeolites are eco-friendly, as they are non-toxic and can be regenerated and reused multiple times. Due to their high surface area, porosity, and unique properties, zeolites are widely used in various industries, such as petrochemical, chemical, and environmental. They have been utilized in gas separation, ion exchange, and as catalysts in numerous reactions, like the conversion of methanol to olefins and the isomerization of n-butane. Furthermore, they are used in water treatment and seawater desalination, as well as for the removal of heavy metals and other contaminants from wastewater. In adsorption heat technology, zeolites are also employed for specific, often extreme driving temperatures.
Metal-Organic Frameworks (MOFs) are a class of highly porous materials composed of metal ions or clusters connected by organic ligands. MOFs have attracted significant attention in the field of water adsorption due to their unique structural features, such as large surface areas, uniform pore sizes, and tunable properties. Water adsorption is the process of attracting and retaining water molecules on the surface of a solid material, with a wide range of applications including dehumidification, air conditioning, and water harvesting. One of the main advantages of using MOFs for water adsorption is their high surface area, which can range from hundreds to thousands of square meters per gram. This large surface area allows a substantial number of water molecules to be adsorbed onto the MOF, resulting in high adsorption capacities. Moreover, the unique properties of MOFs can be tuned by adjusting the metal ions, organic ligands, or both, providing the ability to tailor their adsorption properties for specific applications. The versatility of MOFs has led to their use in various industries, such as gas storage, catalysis, and environmental remediation. In adsorption heat technology, MOFs can be employed to achieve high-performance adsorption cooling and heating systems with lower driving temperatures and enhanced energy efficiency. Their tunable properties, coupled with their eco-friendliness and reusability, make MOFs an attractive option for future adsorption-based applications.
Overall, both zeolites and MOFs have unique advantages and limitations that make them suitable for different applications. In the case of water adsorption, both materials have been shown to be effective in removing water from air or air streams, but the specific choice of material may depend on factors such as pore size, surface chemistry, and environmental conditions.
Furthermore, in Boulton adsorption heat exchangers, the crystalline structure is firmly bonded to the carrier material, providing excellent corrosion protection. Thanks to this innovative material structure, weight, volume and costs can be reduced significantly at the same time.
Adsorption cooling systems, such as those designed by Boulton, are based on solid-state adsorption principles. This is in contrast to absorption cooling technologies, which rely solely on liquid working fluids. In solid-state adsorption, a solid working substance (e.g., silica gel or zeolites) comes into contact with evaporating refrigerant vapor, alternating between desorption and adsorption cycles. As a result, temperature fluctuations occur in chilled water and heat extraction from hot water. By combining two or more modules, near-continuous operation can be achieved, characterized by periodic temperature fluctuations. Consistent temperatures can be easily smoothed with proper buffering if needed. A primary advantage of adsorption systems is the absence of pumps for liquid movement, which eliminates moving parts. This allows the machines to be manufactured simply and compactly. Another notable difference is the lower driving temperatures required by adsorption systems. Compared to absorption systems, our adsorption heat systems perform well within the 50 to 100°C range, while maintaining or achieving higher Coefficient of Performance (COP), indicating greater thermal efficiency.
Adsorption systems reduce the risk of corrosion as adsorbent materials typically do not react with other materials used in the process. In contrast, absorption-based systems often use liquid salts, such as lithium bromide, which can corrode certain metals. Absorption systems also pose toxic risks to the surrounding environment if mechanical components leak or overflow. Furthermore, solid adsorbent materials are more stable and less prone to degradation compared to liquid absorbents used in absorption systems. This can lower maintenance costs and reduce system failures. Adsorption-based cooling systems can achieve higher overall efficiency levels compared to absorption-based systems. This is because adsorption-based systems do not require the high temperatures needed to regenerate liquid materials in absorption-based systems. This can lower operating costs and reduce energy demands.
Specially treated water is used as a refrigerant. Compared to other dominant refrigerants in the thermal industry, water has a large energy capacity, is completely non-toxic and ecologically harmless as a natural substance, and has a temperature range sufficient to cover typical building applications. For Boulton heat pump products, the nominal temperature range for chilled water circuits is from 7°C to ambient temperature. For Boulton dehumidification products, dew point temperatures can reach far below 0°C.
For Boulton dehumidification products, module outputs range from 1 to 50 kW. For Boulton heat pump products, module outputs range from 20 to 100 kW. These machines can also be interconnected in parallel, making virtually unlimited heating and cooling capacities possible. For larger power capacity requirements, customer-specific solutions can accommodate individual needs (e.g., downstream demand, installation space, maintenance options, etc.).
Machines can be installed outdoors in principle, but it is not recommended. In cases of outdoor installation, protection for system technology, such as rain, snow, and frost protection, must be ensured. In cases of frost, hydraulic system freezing must also be prevented. On the other hand, freezing of process water within the cooling device is generally harmless.
All heat pumps can be used as heating and cooling systems in stand-alone installations. To switch between different modes for heat pumps, simply switch the external cooling and cold water circuits to the dedicated spaces. Depending on the installation, this can be achieved using a three-way switching valve.
The relationship between the temperatures of the three circuits and power capacity or COP is best represented by the provided characteristic curves.
In principle, higher source temperaturesincrease power capacity. Higher cold water temperatures increase power capacity and improve COP, while lower recooling temperatures increase power capacity and improve COP as well.
In principle, the machines can be installed in almost any building scenario. Economic viability is ensured by providing heat sources either for free (industrial waste heat) or at least inexpensively (renewable heat). The integration of our products into district heating and cooling systems requires customized design and adjustments tailored to specific needs.
Components and Materials
The heat pump primarily consists of the following components:
- Pairs of adsorption modules
- Adsorbent-coated heat exchanger beds in adsorbers
- Fluid conversion unit, including low-consumption pumps
- Control system, measurement, and regulation technology
- Coated frame/support structure
The cooling modules themselves are corrosion-resistant, as no oxygen is present in the system and carefully selected materials such as stainless steel, copper, and aluminum are used. The support structure and outer casing are typically protected against corrosion with surface coatings, which are suitable for standard indoor installations. However, if the system is to be permanently exposed to higher humidity levels, special corrosion-resistant coatings must be provided.
Boulton primarily uses steel, copper, aluminum, and silicon in production. The adsorbent is environmentally friendly, ensuring that the machine can be disposed of properly at the end of its service life.
Power Source
Unlike traditional compression-based air conditioning, Boulton systems utilize heat in the form of hot water to drive the process instead of electricity. Inexpensive heat, often released into the environment unused or expensively recooled, can be harnessed as the driving source. By using adsorption heat pumps, primary energy can be saved, and the impact of electricity price fluctuations and grid bottlenecks can be better mitigated. Thus, an eco-friendly and resource-saving thermal solution is possible.
The limitation of the source temperature is primarily due to the limited heat resistance of individual materials within the machine. However, safety factors have been considered, so briefly exceeding the maximum temperature is harmless. Persistent, excessive driving temperatures must be prevented through external measures, such as tested and proven return mixtures in heating technology.
Yes, even at driving temperatures below 55°C, a cooling effect is still generated. Moreover, the machine will not automatically shut down. It is advantageous to compensate for short-term temperature drops in the context of continuous cooling and low cycling. However, if this occurs more frequently, it comes at the expense of reduced profitability, as the power demand (e.g., for pumping) remains relatively constant even for lower power capacities.
Due to the varying efficiencies of different collector types and dependence on the installation site, it is not possible to provide a generalized statement. A guideline is that every kilowatt of cooling capacity requires 3-3.5 square meters of collector area. In any case, after determining the required system performance, precise driving power calculations must be performed.
Cooling Water Circuit
Like all thermally-driven cooling systems, adsorption heat pumps rely on recooling the heat generated from converting the supplied heat and extracted cooling capacity. Cooling water ensures that the absorbed energy (during evaporation and desorption processes) can be released back into the environment (during condensation and adsorption processes). If the cooling water temperature rises, the machine’s performance generally decreases. The heat generated by cooling can also be utilized purposefully (e.g., in drying processes, low-temperature heating, swimming pool heating, etc.). In such combined applications, the overall efficiency is particularly high.
Hybrid, adiabatic, or purely wet cooling towers, geothermal probes, seawater heat exchangers, wells, rivers, swimming pools, or other radiators can all be used for recooling.
Cold and Heat Output
Relying solely on the size of the room to be cooled is not sufficient to estimate the cooling load. The latter is significantly affected by insulation standards, window area, and internal loads such as computers, lighting, and occupants. It is recommended to perform an accurate calculation of the required cooling load to appropriately match the product type and cooling demand.
The heat pump cools a constant volume flow of chilled water (coolant), which cools the indoor air as it flows through a chilled water-air heat exchanger (fan coil unit).
We particularly recommend cooling water systems with relatively higher chilled water temperatures, such as:
Floor cooling, wall cooling, ceiling cooling, cooling sails, cooling chambers, concrete core temperature control, forced air coolers, and air distribution systems.
Integration of Adsorption Systems
The combination of heat pumps and CHP is quite common and often very profitable due to the high expected annual operating hours. In any case, the available driving temperature level is sufficient. Compared to solar cooling, CHP allows for round-the-clock cold production. To compensate for fluctuations and potentially temporarily high return driving temperatures, we recommend installing a smoothing buffer downstream of the heat pump. Even with a buffer size of just 120 liters per module, fluctuations in output over time are minimized.
Due to the necessity of placing the recooling unit outdoors and the machine ideally inside the building, this results in physical separation. Long pipe lengths cause higher pressure losses, which require increased pump capacity. Therefore, in cases of long piping, the pipe size must be checked and adjusted if necessary.
When considering the distance to the heat source, it is important to note that heat losses increase with distance, so the heat pump should be placed as close as possible to the heat source. Another factor to consider is that the chiller should preferably be installed near the cooling distribution to prevent the chilled water from warming up.
Project Planning and Design
Economical operation is limited in terms of external temperature, as the COP decreases correspondingly at very high recooling temperatures (depending on regeneration and evaporation temperatures). The exact point of limitation depends on several parameters, such as air humidity. The lower the humidity, the higher the maximum outdoor temperature for operation. Higher external temperatures can also be compensated for with higher chilled water and/or driving temperatures. In principle, it is advisable to opt for climate-independent solutions for recooling at high outdoor temperatures (> 37°C) and high air humidity, such as swimming pool heating, geothermal probes, or seawater heat exchangers. In conditions of high outdoor temperature and constant humidity, wet cooling towers may be the most effective solution. We would be happy to calculate a precise design for you based on potential locations and anticipated operating conditions, including recommendations for the optimal recooling solution.
Cold storage is not necessary. However, a buffer can be used to smooth out the curve and simplify the heat pump’s integration due to the machine’s slightly varying outlet temperatures. Another possible application is to use it as cold storage during nighttime when the sun no longer provides driving energy for the solar thermal heat pump.
With solar collector efficiencies of up to 0.75 and cooling efficiencies of our machines up to 0.7, as much as 50% of the solar radiation energy is converted into cooling power. Regarding power consumption, the achievable efficiency COPe is at least 14. This means that 1 kW of electrical power can generate approximately 14 kW of cooling capacity, with the remaining energy coming from low-grade heat.
Operation and Maintenance
Since there are no moving parts inside the heat pump or heat exchanger, apart from the three-way switching valve and water pump, no further maintenance is required. However, it is recommended to conduct an annual system inspection of the integrated components and materials.
With careful planning and design, the Boulton adsorption machine consumes less than one-fifth of the power of traditional air conditioning units, based on the entire system.
The heat pump can be manually turned on through the controller’s input field or activated by triggering a potential-free contact using a higher-level controller (if provided). All pumps are automatically started by the system. Once started, the machine should be allowed to run without interruptions. Each cycle (on and off) results in energy loss but has no adverse effects on the machine itself.
Heat pump: Dry and, if possible, at a constant temperature between 5 and 45°C, frost-free.
The machine is stable under specified operating conditions. There are no special measures needed to extend its service life.