Expertise: Estimation and data of common ventilation and air conditioning

1. Examples can be given for the calculation of the platform floor, the station hall floor, and the main equipment room, and then the selection of important parameters such as the air leakage volume of the screen door can be specifically explained, so that you can have a preliminary understanding of the design parameters of the subway station.

Thermal index per unit area: residential: 150W/sq.m., office building: 180W/sq.m., restaurant: 250W/sq.m., no specific index for subway stations, need to be calculated.

2. Estimation of main equipment for ventilation and air conditioning:

The main equipment that can be estimated for ventilation and air conditioning is the main engine, cooling water pump, chilled water pump and cooling tower, and the air conditioner has no obvious estimation data relationship because it involves heat and moisture conversion. Generally, Haochen or Hongye software is commonly used to calculate.

The relationship between the cooling capacity of the main engine - the flow rate of chilled water - the flow rate of cooling water is as follows:

Chilled water flow rate = cooling capacity of the main machine * 4.187 / (temperature difference) * 3.6 (unit m3/h)

Cooling water flow = chilled water flow rate * 1.25 (unit: m3/h)

Cooling tower flow = cooling water flow rate * 1.1~1.25 Generally speaking, the selection of cooling tower is conducive to heat transfer

For example, the cooling capacity of the main engine is 1290KW, and the estimated chilled water flow rate is 222m3/h, the cooling water flow rate is 277m3/h, and the cooling tower flow rate is 300m3/h. The design drawings have the same parameters. 3. Fresh air calculation standard:

The public area is the largest of the three, and the screen door usually has the largest air leakage.

When the air conditioning in the public area of the station is running, the following three maximums are taken:

Each calculated person is calculated as 20m3/person·h;

The fresh air volume shall not be less than 15% of the total air supply volume of the system;

Screen door air leakage

When the station adopts four piston air shafts, it is temporarily calculated at 6m3/s

When the station adopts two piston air shafts, it is temporarily calculated at 8m3/s

After the fresh air calculation results come out, it should be checked, and the standard is "fresh air operation in the air-conditioning season of the public area of the station or full ventilation in the non-air-conditioning season: each calculation person is calculated according to 30m3/person·h and the number of air changes is greater than 5 times." ”

Station equipment management room, control center, depot: the fresh air volume of air-conditioning personnel is calculated as 30m3/person·h.

4. Estimated pressure drop of equipment:

Evaporator condenser of centrifugal chiller absorption chiller: pressure drop kPa50~100

Cooling tower: pressure drop kPa20~80

Heat exchanger: pressure drop kPa20~50

Hot and cold water pipe: pressure drop kPa20~50

Fan pipe: pressure drop kPa10~20

Control valve: pressure drop kPa30~50.

5. The distance between the smoke exhaust vent is up to 30m: in fact, it should be the natural flow distance of the smoke.

6. Conversion of several units:

1RT=3.517KU,1M2O=0.01MPa=0.1ATM=0.1bar

7. Water flow rate: generally the chilled water should be less than 2 m/s, and the cooling water can be appropriately amplified, and should not be greater than 2.5 m/s.

8. Nominal diameter of condensate pipe:

Q≤7kWDN＝20mmQ＝7.1～17.6kWDN＝25mm

Q＝101～176kWDN＝40mmQ＝177～598kWDN＝50mm

Q＝599～1055kWDN＝80mmQ＝1056～1512kWDN＝100mm

Q＝1513～12462kWDN＝125mmQ>12462kWDN＝150mm

Along the direction of water flow, the horizontal pipe should maintain a slope of not less than 1/1000, and no stagnant water is allowed.

When the condensate tray is located in the negative pressure section of the unit, a water seal must be set at the outlet of the condensate tray, and the height of the water seal should be about 50% greater than the negative pressure (equivalent to the temperature of the water column) at the condensate tray. The outlet of the water seal should be connected to the atmosphere. In order to prevent condensation on the surface of the condensate pipe, an anti-condensation check must be performed.

Annotation:

(1) When polyvinyl chloride plastic pipes are used, it is generally not necessary to carry out anti-condensation insulation and vapor insulation treatment.

(2) When galvanized steel pipes are used, condensation verification should generally be carried out, and an insulation layer should usually be set.

The top of the condensate riser should be designed with a vent pipe leading to the atmosphere.

9. Design safety factor:

When the equipment of the ventilation and air-conditioning system is selected by using the design calculation value, the cooling capacity of the refrigerator, the cooling capacity and air pressure of the air conditioner, the water flow rate and head of the water pump, and the air volume and air pressure of the fan should all consider a certain safety factor. The final equipment selection parameters (air volume, cooling capacity, full pressure, head, flow rate, etc.) are indicated in the drawings

Air conditioner equipment selection cooling capacity = calculated cooling capacity * 1.1

Air volume of air conditioner equipment selection = calculated air volume * 1.05

Cooling capacity of the chiller = Calculated cooling capacity

Equipment selection flow rate of water pump = calculated flow rate (flow reduction should be considered in parallel working conditions)

Equipment selection head of the pump = calculated head * 1.05

Equipment selection of the fan: air volume = calculated air volume * 1.05

The equipment selection of the fan is full pressure = calculated full pressure * 1.1

Choice of cold water pump

Centrifugal clean water pump with a speed of 30~150 revolutions per second is usually selected, and the flow rate of the pump should be 1.1~1.2 times of the rated flow rate of the chiller (1.1 when a single unit is working, and 1.2 when two units are working in parallel). The head of the pump should be 1.1~1.2 times of the total water pressure drop of the most unfavorable loop of the water supply and return pipe network it bears. The total water pressure drop of the most unfavorable loop includes the water pressure drop Δp1 of the evaporator of the chiller, the water pressure drop Δp2 of the one with the largest water pressure loss of each air conditioning terminal device connected in parallel in the loop, and the sum of the water pressure drop of various pipe fittings in the loop and the pressure drop along the loop. The water pressure drop of the chiller evaporator and the end device of the air conditioner can be found from the product sample according to the design conditions, and the local loss of the loop pipe fittings and the loss along the loop should be calculated by hydraulic calculation, and the loss along the 100m pipe length can be roughly taken as 5mH2O per 100m pipe length when estimating. In this way, if the total length of the most unfavorable loop (i.e., the sum of the length of the supply and return pipes) is L, then the head H (mH2O) of the chiller pump can be estimated as follows.

Hmax=Δp1+Δp2+0.05L(1+K)

where K is the ratio of the sum of the local resistance equivalent lengths to the total length of the straight pipe in the most unfavorable loop. When the most unfavorable loop is long, K is 0.2~0.3, and when the most unfavorable loop is short, K is 0.4~0.6.

Selection of cooling water pumps

1) The flow rate of the cooling water pump should be 1.1 times of the cooling water of the chiller.

2) The head of the water pump is 1.1~1.2 times of the sum of the water pressure drop Δp1 of the condenser of the chiller, the height of the open section of the cooling tower, the loss along the pipeline and the local loss of pipe fittings. Δp1 and Z can be found from the relevant product samples, and the loss along the route and the local loss should be calculated from the hydraulic calculation, when estimating, the local loss of the pipe fittings in the pipeline can be taken 5mH2O, and the loss along the route can be about 5mH2O per 100m pipe length. If the length of the return pipe of the cooling water system is L, the estimated value of the head required for the cooling water pump H(mH2O) is about H=Δp1+Z+5+0.05L

3) According to the flow rate and head of the cooling water pump, the cooling water pump is selected with reference to the performance parameters of the water pump.

Water flow calculations

1. Cooling water flow rate: Generally, the value provided by the product sample is selected, or calculated according to the following formula, and Q in the formula is the refrigeration capacity of the refrigeration host

L(m3/h)=[Q(kW)/(4.5~5)°Cx1.163]X(1.15~1.2)

2. Chilled water flow: The unit selected without considering the simultaneous utilization rate can be selected according to the value provided by the product sample or calculated according to the following formula. If the simultaneous usage rate is considered, we recommend that you use the following formula: Q in the formula is the total cooling load of the building without taking into account the simultaneous occupancy.

L(m3/h)=Q(kW)/（4.5~5）℃x1.163

3. The amount of cooling water replenishment is generally 1~1.6% of the circulating water volume of cooling water.