Introduction to Air Conditioning Cold and Heat Sources

Introduction to  Air Conditioning Cold and Heat Sources

In the past decade, air conditioning technology abroad has developed rapidly, with new technologies, systems, and equipment constantly emerging. Its energy efficiency, environmental friendliness, economy, and comfort are refreshing. Ground source heat pump systems, ice storage low-temperature air supply systems, air conditioning large temperature difference systems, electric thermal storage systems, ductless induction ventilation air conditioning systems, VRV systems, variable air volume systems, building envelope thermal storage systems, and variable water volume systems have successively entered the market, making the original simple and high energy consuming air conditioning systems and equipment look brand new, presenting a new scene of blooming flowers and full of spring colors. In recent years, these new technologies and equipment have also been developed and applied in China, achieving remarkable results. Their outstanding economy, energy efficiency, and environmental protection have led to an increasing number of domestic projects adopting these new technologies and equipment.

Different air conditioning systems can be constructed using different air conditioning equipment and cold/heat sources. The following is a brief explanation:

⑴   Water cooled chiller unit+boiler+air conditioning unit

The centralized and semi centralized air conditioning system composed of water-cooled chillers, boilers, and air conditioning units is currently the most widely used air conditioning system and combination of cold and heat sources in China. Water cooled chillers come in different forms such as reciprocating, screw, centrifugal, and vortex. The chiller, along with the cooling tower and water pump, forms the air conditioning cold source system. Boilers include coal-fired, gas-fired, oil fired, and electric boilers. Air conditioning units can be fan coil units, cabinet air conditioning units, or modular air conditioning units. The advantages are: familiarity with design and management personnel, and reliable use. The prominent disadvantage is that boilers are needed in winter, which results in poor environmental protection.

⑶   Wind cooled hot water unit+air conditioning unit

Centralized and semi centralized air conditioning systems consisting of air-cooled hot and cold water units and air conditioning units, and household air conditioning is this type of system. There are several different forms of air-cooled cold and hot water units, including reciprocating, screw, and vortex. The chiller and water pump form the air conditioning cold and heat source system. Air conditioning units can be fan coil units, cabinet air conditioning units, or modular air conditioning units. The advantages of this combination are that it does not require a boiler and the system is simple. The prominent disadvantages are high energy consumption, limited capacity regulation, high operating costs, and poor heating effect in winter.

⑶ Multi split or multi split variable frequency variable refrigerant heat pump system (VRV system)

The multi split or multi split variable frequency variable refrigerant heat pump system, although originated from the VRV system of Daikin Corporation in Japan, has been developed and improved by various manufacturers. Its basic composition consists of one outdoor unit and multiple indoor units, commonly known as “one to many” among the public. The advantage of this system is that it does not require a boiler and the initial investment is gradually decreasing to an acceptable level. The prominent disadvantages are high energy consumption, high installation level requirements, and poor heating effect in winter.

⑷ Direct fired lithium bromide chiller+air conditioning unit

The centralized and semi centralized air conditioning system consists of a direct fired lithium bromide chiller unit and an air conditioning unit. The direct fired lithium bromide chiller unit has several different forms, including fuel fired and gas-fired, providing cold water in summer and hot water in winter. The chiller unit, cooling tower, and water pump form the air conditioning cold and heat source system. Air conditioning units can be fan coil units, cabinet air conditioning units, or modular air conditioning units. The advantages are: no need for boilers, simple system, poor heating effect in winter, prominent disadvantages are: high initial investment, high operating costs, large machine room area, and poor environmental protection.

⑸ Ground source heat pump

Working principle and classification of ground source heat pumps

Ground source heat pump system is an air conditioning system that uses soil, groundwater or surface water (rivers, lakes, seas) for cold and heat exchange, and uses soil, groundwater or surface water as the cold and heat sources of the heat pump system. In winter, the heat in the ground energy (soil, groundwater or surface water) is extracted and supplied to indoor heating, and the ground energy is used as the “heat source”; In summer, indoor heat is extracted and released into the soil, groundwater, or surface water, where the ground can serve as a ‘cold source’.

Compared with air source heat pumps, ground source heat pumps have many advantages:

◆ Low temperature fluctuations throughout the year. The winter temperature is higher than the air temperature, and the summer temperature is lower than the air temperature. Therefore, the heating and cooling coefficients of ground source heat pumps

To be higher than air source heat pumps, it can generally be higher than 40%, so it can save energy and costs by about 40%.

Winter operation does not require defrosting, reducing losses from frosting and defrosting.

The ground source has a good energy storage effect.

When the cooling load of air conditioning in summer is significantly higher than the heating load in winter, a composite ground source heat pump system is usually used, which embeds pipes based on the heating load in winter, and the excess summer cooling load is eliminated by the cooling tower. Due to the significantly higher price of underground heat exchangers compared to cooling towers, adopting a composite heat pump system can significantly reduce the initial investment.

⑹ Ice storage low-temperature air supply system

The low-temperature air supply system combined with ice storage is an effective means to reduce the initial investment of ice storage systems. The air supply temperature of 4 ℃ to 10 ℃, the initial temperature of cold water of 2 ℃ to 4 ℃, and the temperature rise of cold water of 10 ℃ make the initial investment and operating cost of low-temperature air supply air conditioning systems significantly lower than conventional air conditioning systems, and can achieve better indoor air quality and comfort.

The main characteristics of low-temperature air supply system are:

①   The initial temperature of the cold solution in the low-temperature air supply system is low. When the low-temperature air supply system is combined with the ice storage system, the initial temperature of the cold solution is generally 1 ℃ to 4 ℃, and the standard operating condition is 2 ℃.

② The temperature rise of the cold solution in the low-temperature air supply system is large, and the commonly used temperature rise of the cold solution is 8 ℃~17 ℃. There are two standard operating conditions, namely 10 ℃ and 15 ℃.

③The low-temperature air supply system has a low air supply temperature, generally between 4 ℃ and 10 ℃. The air supply temperature is related to the number of air conditioning units and the inlet air parameters.

④ The indoor air state parameters during low-temperature air supply are different from those of conventional air conditioning systems. Due to low-temperature air supply, the relative humidity of indoor air is significantly lower than that of conventional air conditioning systems, generally ranging from 30% to 40%. The rated operating parameters are: dry bulb temperature t1=26 ℃, wet bulb temperature ts1=15.15 ℃ (relative humidity 30%)

⑤ The number of rows of surface coolers in air conditioning units is higher than that in conventional air conditioning systems. In order to achieve low supply air temperature under low solution temperature and large temperature difference conditions, a larger number of rows of surface coolers must be used, generally 8-10 rows

⑥ To prevent condensation on the surface of the air conditioning unit, the insulation materials and thickness of the unit have been strictly selected and calculated

⑦ Due to the low supply air temperature, it is necessary to consider the temperature rise of the fan and the air duct.