Central air conditioning design
Design order: end first, then host.
Design principle: reasonable and economical, and save the operation cost to the maximum extent.
Design scheme and scope of application:
First, the ending part:
1, fan coil system;
Scope of application: general offices, restaurants and other places.
2. Fan coil plus fresh air system;
Scope of application: offices, hotels, restaurants and entertainment places with high requirements.
3. Full air system;
Scope of application: shopping malls, supermarkets, workshops and other large spaces.
Second, the host part:
1, screw chiller refrigeration, municipal or boiler heating;
Scope of application: there is a dedicated computer room with sufficient power and a special person on duty.
2, air cooling unit refrigeration (heating), municipal or boiler heating;
Scope of application: the air conditioning area is small, there is no computer room and no special person on duty.
3, centrifugal chiller refrigeration, municipal or boiler heating;
Scope of application: the air conditioner has a large area, a dedicated computer room, sufficient power and needs special personnel to be on duty.
4, lithium bromide unit refrigeration (heating), municipal or boiler heating;
Scope of application: power shortage, municipal heat source, comprehensive economy, special computer room and special person on duty.
Third, others:
1, one-to-many system;
Scope of application: places with small air-conditioning area, no special computer room, no special person on duty, large air-conditioning area but not used at the same time, and need independent billing.
2. Pipeline blower system;
Scope of application: large bay, no special computer room, no special person on duty, flexible control and low initial investment.
Design program:
First, the ending part:
(1) equipment selection:
1, calculate the actual air conditioning area;
2. Determine the cooling load index according to the place of use, calculate the total design load, and determine the required number and model of equipment according to the characteristics of equipment layout;
Cooling load budget index:
Use combined air conditioner, the cycle number is 6 ~ 7 times, 8 ~ 9 times is recommended.
(2) Water system design:
1. Locate and arrange the equipment, determine the position of the riser, and decide to adopt the same scheme or different scheme according to the complexity of the system (try to adopt the same scheme when the distance between the riser and the terminal equipment exceeds 30m);
2, determine the direction of the main pipeline, and reasonable connection with the equipment, when the main pipeline has branches, should be set to facilitate the adjustment of the valve;
3. Determine the water flow of each pipe section according to the equipment flow, and then calculate the pipe diameter according to the design water flow;
4. The design flow rate of air conditioning water is 0.9-2.5m/s, and the greater the pipe diameter and flow rate, the specific friction resistance of the pipeline should be less than 500;
5. When the water pipe is connected to the equipment, the water inlet pipe is provided with a hose, a filter and a valve, and the water outlet pipe is provided with a hose and a valve;
6, condensate pipe diameter design:
When the cooling load q of the unit is ≤ 7kW, DN = 20q = 7.1-kloc-0/7.6, DN = 25Q= 17.7- 100, DN = 32q =10. DN = 50Q=599- 1055，DN = 80Q= 1056- 15 12，DN = 100； Q= 15 13- 12462，DN = 125； Q> 12462，DN= 150
7, air conditioning water pipe insulation:
When the ultra-fine glass wool shell is insulated, the insulation thickness of return pipe is 50mm, and the insulation thickness of condensate pipe is 30mm；;
When rubber and plastic materials are used for insulation, the insulation thickness of return pipe is 30mm, and the insulation thickness of condensate pipe is15 mm; ;
When the condensate pipe is made of plastic pipes such as PVC, it does not need heat preservation treatment. One-tow multi-fluorine system should be insulated.
(3) Wind system design:
1, air volume selection:
(1) Fresh air condition: determined according to the minimum fresh air volume per person.
For theaters, museums, gymnasiums and shops, the minimum fresh air volume per person is 8m3/h;
For offices, libraries, conference rooms, restaurants, dance halls and general wards, the minimum fresh air volume per person is17m3/h;
Guest room, the minimum fresh air volume per person is 30M3/H, which is 50m3/h normally;
(2) Return air condition: determined according to the number of cycles, generally 8- 10 times /H, that is, air conditioning space volume × (8-10)/h.
2, the choice of fan pressure:
Estimation method: wind pressure = (the most unfavorable loop length × 10)Pa.
3, equipment positioning, as far as possible close to the water system riser;
4. When arranging tuyeres, on the premise of ensuring no air conditioning dead zone, try to reduce the number of tuyeres and unify the specifications of tuyeres; The wind speed of the air supply outlet is 2-2.5m/s, the wind speed of the air return outlet is 3-5m/s, and the size of the air outlet is determined according to the air volume and wind speed of the air outlet;
5. Determine the direction of the main air duct, and connect it with each air outlet reasonably. When the main air duct has branches, it should be equipped with valves that are easy to adjust, and each tuyere should be equipped with air flow control valves;
6. Determine the air volume of each section of the air duct according to the number of tuyeres, then calculate the cross-sectional area of the air duct according to the design wind speed, and determine the specifications of the air duct according to the installation space. On the premise of ensuring the decoration elevation, try to reduce the height-width ratio of the air duct and reduce the diameter change as much as possible;
Design speed in ventilation and air conditioning ducts (m/s):
Note: 1, the numerator in the table is the recommended flow, and the denominator is the maximum flow.
2. For systems with strict requirements for noise elimination, the velocity in the pipe should not exceed 5 m/s, and the velocity in the branch pipe should not exceed 3 m/s. ..
7. When the air duct passes through the machine room or fire partition, a fire valve should be set on the air duct;
8. When the air volume of the fan is greater than 10000 M3/H, the inlet and outlet of the fan should be provided with a muffler static pressure box, and the cross-sectional flow through the static pressure box is 2-3m/s; When it is less than 10000 M3/H, a muffler can be installed at the outlet of the fan, and the inner diameter of the muffler is the same as that of the main air duct;
9, steel air conditioning duct insulation:
When ultra-fine glass wool board insulation is used, the insulation thickness is 40mm；; When the plastic board is insulated, the insulation thickness is15 mm.
Second, the host part:
(a) refrigeration and heating host:
Determine the load budget index according to the place of use, then multiply it by the total air conditioning area to calculate the total equipment load, and then determine the number of hosts and select the equipment model according to the system situation; For some multi-purpose air-conditioning places, the simultaneous utilization coefficient should be considered when calculating the equipment load.
Air conditioning host load budget indicators:
(2) cooling tower:
According to the required cooling water quantity of refrigeration unit, the actual water quantity of cooling tower should be greater than the required water quantity, and pay attention to that the cooling tower working condition should be consistent with the cooling water working condition of the unit.
(3) Refrigerant water pump:
1, quantity: one more unit as standby;
2. Flow rate: determined according to the cold water flow rate of the unit ×(20~30)%;
3. Lift: According to the system situation, it is generally (20 ~ 40) m;
(4) cooling water pump:
1, quantity: one more unit as standby;
2. Flow rate: determined according to the cooling water flow rate of the unit ×( 10~ 15)%;
3. Lift: according to the height from the water pump to the cooling tower+unit pressure drop+(5 ~10) m; (5) Water softening equipment:
According to the flow rate, it is usually (3 ~ 8) m3/h.
The flow of the make-up water pump should be determined according to the normal and emergency make-up water of hot water, which should be 4-5 times of the normal make-up water. The normal water supply is generally considered as 1% of the system water capacity. In the preliminary design, it can be estimated by 1% of circulating water. The flow of the makeup pump is normal makeup water+emergency makeup water; The flow of water treatment equipment can be determined according to the normal water supply, that is, 1%.
Make-up water can be estimated according to the system load: according to the designed cooling capacity, the water capacity of the system is about 2-3L/KW. According to the estimated interior construction area, it is about per square meter 1 liter.
(6) Softening water tank:
According to the size of the standard water tank, it is usually (2.5~8)M3.
(7) Floor expansion tank:
1. General tank diameter is φ 1000 ~ 1200.
2, with 2 pumps:
Flow: (3 ~ 8) m3/h; Head: (refrigerant pump head × 1.3) m.
(8), water collector, cylinder:
1, diameter d = (1.5-3) × maximum diameter in branch pipe, mm.
2. The length shall be determined according to the number of branch pipes and valve models.
(9) Cooling water treatment:
Usually, an electronic water treatment instrument is set at the cooling water inlet of the unit for treatment.
The constant pressure point of central air conditioning system is generally located on the backwater main pipe at the entrance of chilled water pump, so that the pressure head generated by the pump can be properly distributed in the system. At present, the constant pressure water supply methods of heating and air conditioning system mainly include expansion water tank constant pressure water supply, water supply pump constant pressure water supply, gas constant pressure water tank combined with water supply pump constant pressure water supply and so on. Among them, the expansion tank is the most economical and simple way of constant pressure water supply, so it is widely used in civil buildings now, but the expansion tank must be located at the highest point of the system.