1. The centrifugal pump head estimating method
Hvac centrifugal pump selection: usually choose than revolutions ns in 130 ~ 150 clear centrifugal pump, centrifugal chiller rated flow of centrifugal pump flow rate should be 1.1 ~ 1.2 times (single take 1.1, two parallel take 1.2.Press estimates can take roughly every 100 meters length of the path loss is 5 mH2O, centrifugal pump head (mH2O) :

Hmax = delta P1 + delta P2 + 0.05 L (1 + K)

Delta P1 for chiller evaporator pressure drop.

Delta P2 for the ring in the parallel of the the largest air conditioning end device of hydraulic loss of a water drop.

For the most unfavorable loop length LK for local resistance in the most unfavorable loop combined equivalent length and the ratio of and straight pipe length, when the most unfavorable loop is longer than the K value 0.2 ~ 0.3, the most unfavorable loop shorter take 0.4 ~ 0.6 K value

2. The freezing of head practical estimation method of centrifugal pump
Here talking about the resistance of the closed air conditioning cold water system, because the system is commonly used system.

Drag: 1. The water chiller unit by the manufacturer to provide, generally is 60 ~ 100 kpa.
2. The pipeline resistance: including friction resistance and local resistance, the friction resistance of unit length than the group depends on the technical and economic comparison.If the value is small diameter, initial investment, but the centrifugal pump energy consumption;If small values.The cold water line in the design of appropriate group than the control in 150 ~ 200 (pa/m range, larger diameter, the values can be smaller.
3. Air conditioning end device resistance: the type of terminal device with fan coil units, modular air conditioner, etc.Their resistance was presented according to the design of air into and out of the air conditioning coil parameters, cooling capacity, and poor water provided by the factory after coil configuration computation, many can value the rated conditions on the product samples.The resistance generally in the range of 20 ~ 50 kpa.
4. The regulator resistance: always require control of air conditioning room at room temperature, through setting the electric air terminal device on waterways in two-way regulator is a means to achieve room temperature control.Two of the specifications of the valve by valve fully open flow capacity and allowed pressure drop to choose.If this allowed pressure drop value is large, the control valve performance is good;If small value, the control performance is poor.Valve fully open the pressure drop of the branch of the percentage of the total pressure drop is called right of valve.Rights of the water system design requirements valve S > 0.3, so the two-way regulating valve of allowed pressure drop is generally not less than 40 kpa.

According to the above, can be a rough estimate of about 100 m high a high-rise building air conditioning water system pressure loss, also called circular centrifugal pump head needed:
1. The water chiller resistance: take 80 kPa (8 m water column).
2. The pipeline resistance: take freezer room decontamination, Siamese, manifold and piping resistance of 50 kPa;Take lateral distribution pipe length 300 m and more than 200 Pa/m friction, the friction resistance is 300 * 200 = 200 Pa = 60 kPa;Such as considering the lateral distribution of local resistance is 50% of the friction resistance, the local resistance to 60 kPa * 0.5 = 30 kPa;System total resistance of pipeline for 50 kPa + 60 kPa + 30 kPa = 140 kPa (14 m water column);
3. The resistance of the combined air conditioner generally larger than the fan coil resistance, therefore, take the former resistance to 45 kPa (4.5 water column);
4. The two-way regulating valve resistance: take 40 kPa (4.0 water column).
5. As a result, water system of the resistance to the sum of the parts: 80 kPa + 140 kPa + 45 kPa + 40 kPa = 305 kPa (30.5 m water column)
6. centrifugal pump head: take the safety factor of 10%, the head H = 30.5 m * 1.1 = 1.1 m.

According to the result of the above estimates, can master basic similar size of the structure of the air conditioning water system pressure loss value range, especially should prevent because of without calculation, too conservative, and the system pressure loss estimation is too large, the centrifugal pump will choose too large, lead to waste of energy.

The formula of centrifugal pump

Head for the unit mass of effective energy after the liquid flows through the pump.Is an important work of pump parameters, also known as the pressure head.Can be said as the pressure of the fluid to the increase of the head, the kinetic energy and potential energy, namely

H = (p2, p1)/rho g + (c2 c1) / 2 g + z2 - z1 type of H - head, m;

P1, p2, import and export of liquid pump pressure, Pa.

Import and export of c1 and c2 - fluid in the pump velocity, m/s.

Z1, z2 - height of imports and exports, m;

Rho, liquid density, kg/m3;

G - the acceleration of gravity, m/s2.