How can building automation systems achieve energy savings?

The intelligent office building combines computer technology, communication technology, information technology and building technology to provide people with a safe, efficient, comfortable and convenient building environment through the building automation system. The building automation system can improve the performance of construction equipment. By fully utilizing the operational efficiency of the controlled equipment, realizing energy optimization scheduling within the building and reducing operating costs, it is an energy-saving technology with deep potential and potential in building intelligentization.

The use of the building's self-control system, the central "brain", to carry out energy conservation and emission reduction of existing buildings is an important manifestation of the management level and competitiveness of the property company. This paper combines the property management experience and energy-saving control cases of the office building, analyzes the problems existing in the property management system of the building automation system and how to improve the management level of daily equipment and exert its energy-saving potential.

Problems faced by building automation systems in property management

At present, the function of the building automation system as the “brain” of the building equipment operation center is often not fully exerted. The building automation system is often in the basic function stage of realizing the simple start, stop control and real-time monitoring of remote equipment. The effect of the operating state of the equipment system, thus restricting the mining of energy saving potential.

For the energy conservation of existing intelligent buildings, achieving unified planning and selecting a reasonable technical route is the key to achieving energy-saving goals. The so-called energy saving can be roughly divided into two aspects. First, aiming at the use needs of users in the building, achieving energy supply and demand balance and avoiding energy waste. The second is to replace the old high-energy equipment and insulation materials through equipment or material renewal.

At present, many units still have limitations in the understanding of energy-saving work. They believe that energy-saving is to update equipment, that is, to replace more energy-saving lamps and introduce more energy-saving insulation materials. It is true that energy saving can be achieved quickly in this way, but the return on investment is longer than that of the huge investment required to purchase new equipment and materials, and some even have more than 10 years.

By adjusting the balance of energy supply and demand in the building, the cost of input is relatively small, but it is necessary to improve the comfort of the public area and provide comfort to the owners through scientific control, based on a deep understanding of the various energy needs in the building. Work and living environment, which needs to be realized through the existing building automation system.

Analysis of the Phenomenon and Causes of Uneven Distribution of Cold Sources

Air-conditioning systems account for the largest energy consumption in building construction, about 40% to 60%, so energy-saving control of air-conditioning equipment is particularly important. Air-conditioning systems are usually designed with the hottest and coldest weather and the highest load conditions, and 10% to 20% of the design allowance is reserved. In view of the fact that most of the time in the actual operation of the building will not work at full load, the air conditioning system actually has a large operating margin.

Therefore, energy-saving control of air-conditioning equipment through building automation systems can significantly reduce energy consumption, improve equipment efficiency, and bring significant economic benefits. In the following, combined with the author's example of energy-saving control of the office building, how to use the building automation system to run the program to achieve a reasonable deployment of the overall cold source of the office building.

Case Background: An office building was completed in 1997. There are four single buildings A, B, C and D. The system cold source is provided by a freezing station in the underground of Block A. Among them, Building D is a canteen, conference use, two underground floors and three floors above ground, with a total construction area of ​​about 10,000 square meters. In addition to the three floors above the conference hall, the second floor to the second floor are restaurants and canteens. The conference hall can accommodate up to 800 people and is an important venue for large-scale conferences and performances. From the perspective of the air conditioning system, the conference hall is at the end of the supply of cold source for the D building. As the temperature rises year by year and the equipment ages, there is a significant shortage of refrigeration efficiency in the conference hall. Especially in the summer when the outdoor temperature is high, it is impossible to ensure that the temperature in the field is controlled within a comfortable range.

In order to solve the above problems, there are mainly two options to choose from.

One is the conventional scheme of adding cold source operation equipment (freezer, chilled water pump, etc.). Although this method can meet the cold source demand of the conference hall, it is easy to appear due to the excessive supply of cold source of other air conditioning units, resulting in a low temperature difference between the overall supply and return of the chiller, poor cooling efficiency, and a substantial increase in equipment. Operating expenses and workload for maintenance and overhaul in the future;

Another solution is to optimize the distribution of existing single-pump cold-source supply, and adjust the existing control procedures to tap the energy-saving potential without investing more operating equipment. In order to realize the second scheme, we first carried out system inspection on the D-seat air-conditioning system, from waterway (pressure, flow), wind path (air volume) and automatic control system (sensor, actuator, control program).

From the test results, the flow distribution of the cold source water supply in Block D is uneven. In the case of single refrigeration pump operation, the cold water supply flow rate of the 3rd floor conference hall is mostly intercepted by the 1st and 2nd floor canteens, resulting in the temperature difference between the supply and return water in the canteen. The small temperature difference between the small and the conference halls makes the temperature control of the conference hall not guaranteed in time.

There are three main reasons for this problem:

(1) The control schedule of the air conditioner is unreasonable

From the time of energy use demand, the use time of canteens, kitchens, and conference halls is not exactly the same, and the dining hall peaks are generally different from the meeting time. Therefore, the air-conditioning units in the above three areas should be started and stopped according to the actual demand of the cold source, but the initial control procedures of the air-conditioning units of the building automation system are all in the same time, resulting in the centralized use of cold sources in each area at the same time. The phenomenon that the supply of cold source does not correspond to the actual demand.

(2) Failure to effectively utilize natural cold sources

At present, the fresh air control of each air conditioner in Block D adopts the mixed air control mode of 20% fresh air 80% return air, because the fresh air temperature varies with outdoor time, when the temperature is low and the humidity is suitable in summer (especially at 5 o'clock in the morning) At 8 o'clock, natural cold source should be used more, and when the outdoor temperature is high, closed loop (ie full return mode) or minimum fresh air mode can be adopted when the indoor air index (ie, the upper limit of carbon dioxide concentration) is satisfied. To save cold source demand.

(3) The fan frequency failed to make an effective immediate adjustment

At present, the D-seat air conditioning unit is equipped with a frequency converter, but the frequency is not dynamically controlled. When the outdoor temperature is low, the frequency of the air conditioner can be increased, and the natural cold source can be utilized efficiently. When the temperature difference between the supply and return water of the air conditioning system is small and the utilization rate of the cold source is low, the method of increasing the frequency of the air conditioner can also be adopted to increase the air volume per unit time, increase the total amount of heat exchange, and thereby improve the temperature difference between the water supply and the return air. Make full use of the cold source.

Optimized energy-saving operation plan for cold source supply scheduling

In response to the above problems, we adopted an optimized control method, with the principle of “time sharing, segmentation, and temperature separation” as the guiding principle, and the cold source is allocated according to the usage. The specific contents are as follows:

In view of the different cold source time requirements of the D-story 3rd floor conference hall and the D other canteen areas, we control the fan return water valve through the building automation system to meet the respective usage requirements in different time periods. In the morning, especially from 9:00 to 11:00, the whole system gives priority to the cold source of the kitchen, and from 11:00 to 1:00, the priority of the cold source in the cafeteria is given priority. At other times, priority is given to ensuring the cooling demand of the conference hall. When the return water temperature is too high, and then there is insufficient cold source, the set temperature of the restaurant can be raised, and the water valve opening of the canteen air-conditioning unit can be controlled to be cold. The source gives priority to meeting room requirements.

At the same time, if the conference hall is to be used in the morning, it is controlled by the pre-cooling scheme, that is, the air-conditioning unit of the conference hall is turned on at 5:00 am every day to lower the room temperature to a lower value. If the outdoor temperature is low, the fresh air valve can be fully opened, and the fan frequency can be turned up to 50 Hz. The indoor temperature should be controlled within the indoor range of 21 °-22 ° before 7:00. After 7:00-8:00, the indoor temperature is controlled within the range of 24°-26° by using the cold storage capacity of the conference hall enclosure structure, and the opening of the fresh air valve is reduced as the outdoor temperature increases. Indoor temperature control needs at the meeting.

From the practical point of view, real-time control of the air-conditioning equipment start-stop time, fan frequency, fresh air valve opening and water valve opening degree through the building automation system achieves the effect of optimizing the cold source distribution mode, without opening other freezes. In the case of the unit and the chilled water pump, the optimized supply of the cold source is realized, and the operation of the cold source system equipment is increased due to insufficient cold source demand of the conference hall, resulting in waste of the cold source.

After the building has been put into operation, according to the actual use function of the building and the equipment load, the operating state of the equipment system is precisely adjusted, and energy-saving operation is realized under the requirement of ensuring the comfort of the indoor space. It is a comprehensive and systematic quality control process. Property management personnel need to fully understand the characteristics of energy demand in buildings, master the operation principle of building automation system and controlled equipment, and aim at the overall energy allocation of office buildings, and allocate existing energy supply to achieve energy saving effect. In order to achieve a win-win situation between corporate benefits and social benefits.