What are the design points for HVAC in commercial buildings?

With the sustained and rapid development of our country's economy and the improvement of people's living standards, a large number of commercial buildings in our country have also been constructed. At the same time, more and more commercial buildings have installed central HVAC. However, during its operation, it generates a large amount of power, causing the building to consume too much energy, which is not conducive to the urban environment. If we design it reasonably and effectively control its operating mode, we can effectively reduce the energy consumption of HVAC. This article focuses on the issues that should be considered in the design of commercial building HVAC, and elaborates on the key points of commercial building HVAC design.

1. Characteristics of air-conditioning design of commercial buildings

The air-conditioning design of commercial buildings is different from buildings such as residences, office buildings or hotels. It has the following characteristics:

(1) The plane building space is large and the load is small

The plane building space of commercial buildings is large. In order to attract customers' attention and make them stay on the dazzling array of products indoors, in addition to advertising windows, shopping malls Most of the peripheral structures of the building are designed to be closed (even the glass curtain wall), so the heat transfer and radiation loads of the building envelope are relatively small.

(2) Cooling load accounts for a large proportion

In order to ensure the lighting and advertising effects of commercial buildings, shopping malls use many types of lighting equipment with high heating values ??(such as projector lights , halogen lamps, etc.), especially for some special commodities (such as jewelry), so the cooling load generated by lighting accounts for a larger part of the air-conditioned indoor load.

(3) Large personnel and fresh air load

Commercial buildings have high personnel density, so the personnel load and fresh air load are both large, and the quality of indoor air completely depends on the air conditioner. fresh air system.

(4) Air-conditioning equipment is flexible

Some layouts of commercial buildings will change with seasons or needs, so air-conditioning equipment is required to have a certain degree of flexibility.

II. Issues that should be considered in the design of commercial building HVAC

(1) Feasibility and reliability issues

Being able to meet the usage requirements, this This is the main issue that should be considered for the feasibility of the program. The design scheme should comply with the requirements of relevant national and local government laws and regulations, including requirements related to environmental protection. The design scheme should be able to meet the requirements of relevant parties (such as power supply, gas supply, water supply, heating supply, etc.), and special consideration should be given to these Long-term, changing conditions. For example, when adopting a water source heat pump design scheme, issues such as local geological conditions, the current status and changing trends of groundwater resources, and the heat (cold) accumulation effect caused by the imbalance of winter heating load and summer cooling load should be considered. The available area in commercial buildings is very precious, so the equipment room area is extremely streamlined. Especially on the first floor of shopping malls, ceiling-mounted air conditioners are mostly considered to save building area.

(2) Economic comparison issue

Economic comparison is currently the most considered issue in the comparison of commercial air conditioning solutions. The same design requirements, usage conditions, equipment grades, energy prices, comfort conditions, aesthetic conditions and other benchmark conditions should be used for comparison, so as to ensure the scientificity and rationality of the plan comparison results. It is obviously unreasonable to make an economic comparison between plans using famous brand equipment and low-end equipment; without considering the difference in comfort, it is obviously impossible to make an economic comparison between plans with fresh air supply and without fresh air supply. The right choice; it is obviously unfair to make an economic comparison of centralized air conditioning solutions without considering aesthetics and comfort.

Operating energy consumption and operating costs are important parameters that must be considered in the technical and economic comparison of HVAC design solutions. In addition to calculating the energy consumption of the HVAC host (boiler and refrigeration machine, etc.), the operating energy consumption should also calculate the energy consumption of other auxiliary equipment (such as fans and water pumps, etc.).

(3) Adjustability and operability issues

The capacity of the air-conditioning system of commercial buildings is usually determined based on the most unfavorable weather conditions throughout the year. However, due to the current lack of insulation in shopping mall buildings Very well done. In addition, most buildings have no windows, so seasons have little impact on temperature during most of the year. Nowadays, more and more cooling equipment in shopping malls cause indoor temperatures to be high, and the outdoor environment has little impact on it. . Therefore, it is mostly not used in terms of adjustment.

The improvement of the automation level of air conditioning systems can reduce the number of management personnel and labor intensity, thereby reducing labor costs, but increasing primary investment and raising requirements for the quality of operators.

Whether the air conditioning system adopts automatic control should be determined based on the actual situation and requirements and a technical and economic comparison. For large air conditioning systems and projects with many equipment that require frequent adjustment and control, automatic control should be used to reduce the workload of operation and management. However, the automatic control system should be simplified as much as possible to improve the economy and reliability of the system.

(4) Safety issues

The safety of HVAC systems mainly includes the safety of flammable and explosive environments, fire safety, personnel environmental safety, environmental safety of important equipment and items, and system There are five aspects of equipment operation safety.

Personnel environmental safety mainly includes three aspects: the harm of HVAC systems to the human body, prevention of terrorist attacks, and prevention of the spread of infectious diseases. In terms of preventing terrorist attacks and preventing the spread of infectious diseases, it should be noted that the fresh air vents of air conditioners are the weakest link, so reliable preventive measures must be taken. The fresh air vents should be set up in places that are difficult to access and are not easily contaminated. Since most shopping malls have all-air air conditioning systems with many return air outlets, they are the form of air conditioning system that is most vulnerable to biochemical attacks by terrorists. If special measures are not taken, it is also the form of air conditioning system that is most likely to cause the spread of epidemic diseases. When determining the fresh air volume of the system, in addition to considering some past factors, the requirement to dilute the concentration of harmful indoor viruses during an epidemic outbreak must also be considered.

3. Parameter selection and load calculation for commercial building air conditioning design

(1) Indoor temperature and humidity

The indoor temperature of shopping malls must take into account the requirements of customers , but also consider the requirements of shopping mall staff. In summer, because customers often come in and out, the temperature in the mall can be lower, but low temperature is not good for the health of the sales staff. Methods should be used to increase the room temperature and reduce the humidity; in winter, customers wear cold-proof coats, and sales staff are in the store for a long time. When working in a shopping mall, you should not wear too much clothing. All things considered, the temperature needs to be slightly higher. Since the human body emits more latent heat in winter, there is no need to think too much about humidification.

(2) Summer air-conditioning cooling load

The summer air-conditioning load of shopping malls mainly includes the heat transfer and insolation of the building, human body, lighting and other electrical equipment, escalators, fresh air, etc. Among them, fresh air load, human body load and lighting load are the main ones. The building load is very small, accounting for only 2 to 5% of the total load.

1. Human body load

Human body load is a large part of air conditioning load in summer. The determination of personnel density directly affects the size of personnel load. Nowadays, some large department store operators always hope that their shopping malls must have a certain flow of people and maintain a relatively high level. Therefore, the density of people should not be as high as the previous design. Nowadays, the recommended personnel density for general large-scale shopping malls is as shown in Table 2, which is set at about 1.5 to 2.0 people/m2. Even on the first floor, it should not exceed 1.0 people/m2.

2. Lighting load

With the importance of merchants on product display and the emergence of various small counters or specialty stores in large shopping malls, the requirement for high illumination has become more and more obvious. Moreover, large department stores are often used to sealing off the surrounding exterior walls and designing them to be closed in order to keep customers' eyes on the dazzling array of merchandise. As a result, the capacity of the lighting load also increases, and its proportion in the total load also increases. The higher. Moreover, most of the lamps used in shopping mall displays have high calorific value, further exacerbating the increase in lighting load.

3. Outdoor fresh air load

Due to the relatively high indoor density of people, commercial buildings must have sufficient outdoor fresh air. According to relevant specifications, the load calculation is based on 8.5~15m3/h per person.

4. Noise requirements

Most commercial buildings are located in bustling and bustling cities, with relatively large environmental noise. Reasonable noise reduction measures should be taken into consideration when designing air conditioners. The allowable noise level of general business halls is NC50~55dB, the allowable noise level of high-end shopping malls is NC40~50dB, and the allowable noise level of shopping malls with special requirements, such as musical instrument stores, is NC35~45dB.

In the noise reduction design, the air supply volume of each air supply outlet should be close to the design value. If the air supply volume is much larger than the design value, the air supply outlet will emit noise. In this case, use the louver at the air supply outlet to adjust the air volume. When the air volume is small, the noise will be greater. The allowable wind speed at the air supply outlet of the shopping mall is 7.5m/s, and can reach 10m/s on the first floor. The allowable wind speed of the return air outlet is related to its location. When it is close to people, it is 1.5~2m/s, and when it is far away from people, it is 3~4m/s. For situations with noisy streets and poor sound insulation of windows, there is no need to keep the noise of the air conditioning system very low.

IV. Air conditioning methods in commercial buildings

(1) The most commonly used air conditioning methods in commercial buildings

In the current design of air conditioning systems in commercial buildings, constant air volume air conditioning system is the most adopted. The reasons are as follows:

1. Because the air conditioning unit is placed in the machine room, it is easy to operate and maintain, and can perform complete air filtration. There are fewer problems with vibration and noise transmission.

2. Due to the large air supply volume and sufficient ventilation, especially if a return air fan is installed, fresh air can be used for cooling in winter or transitional seasons.

3. When there are fewer partitions, the equipment fee is cheaper than other methods. Compared with the variable air volume method, this method has the following disadvantages: the fan supply power is large throughout the year, which is not conducive to energy saving. Since it cannot adapt to the load changes of each store in a certain zone, resulting in temperature fluctuations between stores, in large shopping mall buildings, it is replaced by using it in conjunction with unit units. In the future, it can be considered to gradually move to variable air volume. way transition.

(2) Air-conditioning system selection

For commercial buildings, the air-conditioning system method is more flexible, and all-air systems, air-water systems, or even both can be used. used in combination. Because of the characteristics of large commercial buildings and certain advantages of all-air systems, the design of all-air systems is extremely common in large commercial buildings.

1. Air-water system

The common way is to deal with fresh air + fan coil. This type of system is highly flexible and can be controlled independently. It can make timely changes to large-scale changes in functions and layouts in the mall, and the secondary system occupies less ceiling space.

However, this system is designed according to the minimum fresh air volume, and the air quality and comfort are limited; the water pipes are also subject to construction factors, which can easily cause water pipe leaks and condensed water dripping from cold water pipes in summer, which brings great problems to the shopping mall. It will bring losses; and there are many equipments, which will cause troublesome maintenance and heavy maintenance work in the future.

2. All-air system

For commercial buildings with large spaces, as long as the floor height is sufficient, the all-air system is the best air conditioning method. The air that is cooled and heated by the central air-conditioning box is transported to the air-conditioned area through the air duct.

This type of system has a large number of ventilations and good human body comfort; it can use fresh air for cooling in transitional seasons to save energy; and the system is simple and easy to maintain. However, the disadvantages are that the air duct section is large, takes up a large building space, and the layout is inflexible. When the layout changes significantly, it cannot meet the decoration requirements.

3. Ceiling air conditioner system

The ceiling air conditioner system is an air conditioning system developed in recent years. It can save the area of ??the machine room, reduce the building height, and save money. Air duct. The ceiling-mounted air conditioning unit is installed in the ceiling of the use space. The noise of the unit is not only transmitted through the air outlet, but also directly radiated. Therefore, the noise problem is a major problem for the ceiling-mounted air conditioning unit. Secondly, there are many water supply and return pipes, and the water pipes are installed in the suspended ceiling, which increases leakage and dripping. The limited fresh air volume is also a major disadvantage of ceiling-mounted air conditioning units. Since there are many air ducts, water pipes and other pipes under the beams, the fresh air ducts are restricted, so the ceiling-mounted air conditioning system only has limited fresh air in the outer area.

4. Variable fresh air ratio system

In fact, the variable fresh air ratio system is a type of all-air system. However, because this system is extremely popular in large department stores, it is not detailed Explain.

As the name suggests, the new wind ratio system is changing. The design of the secondary system takes into account the different seasonal climate changes throughout the year, and changes the fresh air volume to achieve a comfortable indoor environment with as little energy consumption as possible. Therefore, this system is an energy-saving system, especially in the transition season.

(3) Airflow organization in commercial buildings

At present, in commercial buildings, the methods of upper air flow and lower air flow, upper air air flow and side air flow and side air flow and lower air flow are mostly used, and bottom air flow and upper air flow are also used. Although the return method can reduce the indoor load, it can easily cause dust on the ground to rise, which is detrimental to human health and the indoor air environment, so it should be used with caution. When the return air outlet is located on the ground, in order to prevent paper scraps, cigarette butts, etc. from being inhaled, a wire mesh should be installed inside the return air outlet, and holes that can remove dust should be installed on the return air duct and cleaned regularly.

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