A summary of common knowledge points and problems in HVAC design and how to solve them?

What are the common knowledge points and problems in HVAC design and their specific solutions? Zhongda Consulting will answer them for you below.

The design position of the water pump in the system

Generally speaking, the chilled water pump should be located at the front end of the chiller, and the chilled water coming back from the end is returned to the chiller through the chilled water pump; the cooling water pump should be On the water path where the cooling water enters the unit, the cooling water from the cooling tower is returned to the unit through the cooling water pump; the hot water circulation pump is located on the return water main pipe, and the hot water coming back from the end is returned to the plate heat exchanger through the hot water circulation pump. device.

Valve design on the cooling tower

1. Add a solenoid valve to the water inlet pipe of the cooling tower (the use of manual valves is not recommended)

2. Pipe drain valve It should be installed indoors (if it is placed outdoors, it will freeze easily in winter because there is some water in the pipe).

The installation position of the electronic water treatment instrument

is placed behind the water pump and in front of the main unit.

Valves before and after the filter

Put pressure gauges before and after the filter.

Valves before and after the water pump

1. The water pump inlet pipe is connected in order: butterfly valve-pressure gauge-soft connection.

2. The water pump outlet pipe is connected in order: soft joint - pressure gauge - check valve - butterfly valve.

Water distributor/collector

1. Add an electric differential pressure bypass valve and bypass pipe (pipe diameter is generally DN50) between the distributor/collector.

2. A thermometer should be installed on the return pipe of the water collector.

Location of various instruments

Arrangement of temperature gauges, pressure gauges and other measuring instruments should be located in places convenient for observation. The height of the valve is generally 1.2-1.5m above the ground, and higher than this When the height is high, a working platform should be set up.

Location of the unit

The distance between the protruding parts of the two compressors is less than 1.0m, the distance between the refrigerator and the wall and the distance between the non-main channels is not less than 0.8m, The distance between large and medium-sized refrigeration units (centrifugal, screw, absorption refrigeration units) is 1.5-2.0m. It is best to reserve hooks for lifting the largest components or install electric lifting equipment in the upper part of the refrigeration machine room of the refrigeration unit.

Problem 1: The slope of the water pipe must be reasonable

1. Horizontal branches and main pipes should maintain a slope of no less than 0.002 along the direction of water flow;

2 . The slope of the drainage branch pipe of the unit water pan should not be less than 0.01.

3. Due to limited conditions, it can be laid without slope, but the flow rate in the pipe shall not be less than 0.25m/s.

Problem 2: Design of condensed water main pipe

1. Condensed water should be discharged nearby, usually to the bathroom floor drain.

2. When designing the length of the condensate main pipe, the height caused by the slope should be considered. The height difference between the two ends of the pipe should not be greater than the height of the ceiling.

Problem 3: Select appropriate pipeline valves

1. Install a regulating valve at the connection between the vertical pipe and the horizontal pipe

3. Each part of the water pipeline An exhaust device is installed at the highest point (when laid without slope, at the end of the horizontal pipe flow)

3. A shut-off valve is connected to the lowest point of the riser to facilitate maintenance of the riser

4. Thermal compensation of water pipes can be compensated naturally by using elbows. When insufficient, an expansion compensator can also be added

Problem 4: Water pipe layout

1. Riser pipes should not be placed in pipe wells If placed randomly, it should be placed against a wall or in a corner (see attached picture)

2. Pipes are not allowed to pass through stairs, shear walls, distribution rooms, etc. in the horizontal plane

Problem five: Water pipe insulation

1. The insulation structure is generally composed of an insulation layer and a protective layer

2. The thickness of the insulation layer should be determined based on thermal calculations. For empirical values, please refer to "Civil Building Air Conditioning Design".

3. Insulation materials can be adapted to local conditions and sourced from nearby materials. Non-flammable or flame-retardant materials should be used and must comply with the "Fire Protection Code for Building Design".

Problem 6: Hydraulic calculation

1. The difference in pressure loss between parallel loops of the air-conditioning water system should not be greater than 15;

2. Water pipeline ratio Friction should be controlled at 100-300Pa/m.

Problem No. 7: Water system replenishment

1. The air-conditioning water system replenishment should be treated with softened water. Only summer cooling systems can use electronic water treatment devices;

2. The system water replenishment amount should be 2 times the system water capacity;

3. The water replenishment point should be located at the suction section of the circulating water pump.

Problems that should be paid attention to in the end design

1. For the design of the air outlet of the air disc connected to the air duct, see the attached figure.

1) The distance between the first air supply port and the air outlet of the wind disk must be appropriate;

2) The diameter of the air supply duct of the air disk with two air outlets must be changed;

3) The distance between the air supply outlet and the return air outlet of the fan disk should be appropriate. (≤5 meters)

2. For the design of the water inlet and outlet pipelines of the fan coil unit, see attached figure 1-2.

1) The water inlet and outlet pipes are "top in and bottom out";

2) The relative elevation between the fan disk and the water supply and return main pipe is not less than 200mm;

3 ) Connect the filter, gate valve, and soft joint to the water inlet pipe in sequence;

4) Connect the soft joint and gate valve to the water outlet pipe.

3. Determination of the number of air outlets of the same type of fan disk

The number of air outlets of the same type of fan disk may vary depending on the air conditioning area, see attached figure 1-3.

4. Two small private rooms must use one fan disk for airflow organization

Two small private rooms must use one fan disk. Each private room can have an air outlet, and the return air outlets of the two private rooms can pass through Connect in series to the return air outlet of the fan coil.

5. Fan coil arrangement near the window:

To resist the penetration of outdoor cooling load, the fan coil unit should be arranged as close to the exterior wall and exterior window as possible.

6. Arrangement of fan coil units in large spaces:

When arranging fan coil units in large spaces, it is advisable to arrange the fan coils in an airflow arrangement with air return in the middle and air supply on both sides.

7. Layout of embedded machines: When arranging embedded machines, the distance from the side wall shall not be greater than 3 meters;

When arranging embedded machines in conference rooms, multi-functional halls, etc., multiple machines with small cooling capacities should be used and arranged evenly .

8． Selection of indoor machines: embedded machines can be used for large spaces, and cassette machines are best for rectangular offices.

9. Air outlet selection: It is not advisable to use a diffuser for air supply in a high space (the wind should not be delivered to the work area). It is best to use an adjustable double-layer louver air supply outlet.

10． How to use return air box:

Return air design of air handler: build a relatively large return air box at the return air place, and open a return air outlet on one side of the return air box. This method can adjust the air flow and reduce noise).

11. Design an appropriate fan disk according to the room function and cooling load.

The fan disk selection should be based on the design load, and the fan disk layout should consider the characteristics of the air-conditioned room and try to make the layout as beautiful as possible.

12. The distance between the air supply and exhaust outlets should be appropriate.

Keep a distance of at least 3 meters between the exhaust outlet and the air supply outlet to prevent air flow short circuit.

13． Choose an appropriate damper.

In principle, the system air pressure balance error is within 10%-15%, and there is no need to set up a regulating valve. However, in fact, it is very difficult to adjust the air pressure solely based on the size of the air regulating duct. Therefore, an air volume regulating valve must be installed for adjustment.

① An air volume regulating valve should be installed at the branch of the air duct. A three-way regulating valve can be installed at the three-way branch, or a regulating valve can be installed at the branch.

② The obviously unfavorable loop may not have a regulating valve to reduce resistance loss.

③ Where a fire damper is required, a fire regulating valve can be used instead of a regulating valve.

④ The louver air outlet at the air supply outlet should be an air supply outlet with a regulating valve. If the requirements are not high, a double-layer louver air outlet can be used, and the air volume can be adjusted by adjusting the angle of the air outlet.

⑤ A damper that can be opened and closed tightly should be installed at the fresh air inlet. An insulation damper should be installed in severely cold areas. When automatic control is available, an electric damper should be used.

14． Air duct layout.

① Local resistance should be reduced as much as possible, that is, the number of elbows, tees, and diameter reductions should be reduced.

② The central curvature radius of the elbow should not be smaller than the diameter or side length of the air duct. Generally, 1.25 times the diameter or side length can be used.

③ In order to facilitate the adjustment of the air duct system, pressure measuring holes should be reserved before and after the branch points of the main pipe. The distance between the pressure measuring hole and the local pipe fittings in the front should be greater than 5b (b is the long side of the rectangular air duct or the diameter of the circular air duct), and the distance from the local pipe fittings in the back should not be less than 2b. A pressure measuring hole should be reserved on the pipe section with relatively stable air flow at the outlet of the ventilator.

15． Location of fresh air inlet

① The air inlet should be located in a place where the outdoor air is relatively clean to ensure air quality.

② It should be located on the north wall, avoid being located on the roof and west wall, and should be located in the shade of the building so that the temperature of the outdoor air inhaled in summer can be lower.

③ The distance between the bottom of the air inlet and the outdoor ground should not be less than two meters. When the air inlet is arranged in a green belt, it should not be less than one meter.

④ It should be arranged on the upwind side of the exhaust outlet and lower than the exhaust outlet, and try to keep a distance of no less than 10 meters.

16． Requirements for fresh air outlets

① Fixed blinds should be used.

② In rainy areas, waterproof blinds should be used to prevent rainwater from entering.

③ To prevent birds from entering, metal mesh should be installed inside the shutters.

17. New methods for exhaust ducts

The design of an exhaust system similar to hotel rooms can be considered as follows: use an exhaust fan to exhaust indoor air into the ceiling of the corridor. An exhaust duct is provided to exhaust air. In order to effectively utilize waste heat, an exhaust fan can be installed in the bathroom.

18. The distance between the air outlet and the side wall: the distance between the air outlet and the wall should not be less than 1 meter.

19. Selection of air outlets:

① Use double-layer louver air outlets for fresh air outlets and supply air outlets;

② Use grille air outlets for return air outlets;

③ Use double-layer louvers for the air exhaust outlet;

④ Since the air volume of the fluorine system is generally relatively small, if heating is required in winter, double-layer louvers should be used instead of a diffuser.

⑤ When the fan coil unit has two air outlets, double-layer louvers with regulating valves should be used.

20. Condensation at the air outlet

Condensation at the air outlet is due to the small air outlet and low temperature. The size of the air outlet can be increased to prevent condensation.

21. Calculation of static plenum box

① The controlled wind speed of the static plenum box should not be greater than 1.5m/s

② The air outlet cross-sectional area A=G/V (G is the air supply volume), The cross-sectional area in all directions should be the same

③ In general systems, the static pressure box can be replaced by a variable diameter tuyere and a silencer

22. Determination of the number of ventilations for smoke prevention and exhaustion.

① No less than 4 times in the fire pump room

② 5-8 times in the transformer room

③ 5-8 times in the transformer room

23. The arrangement of smoke exhaust vents.

① The corridor is more than 60 meters long and should be used as a smoke exhaust outlet.

②The elevator front room uses a normally open multi-leaf air supply vent, one on each floor.

③ Use self-hanging louver air vents in the stairwell, one on the 2-3 floors.

24. The air pressure status of the room.

① The air-conditioned room in the building should maintain positive pressure.

② Toilets, washrooms, and various equipment rooms in the building should maintain negative pressure.

③ Positive pressure should be maintained in hotel rooms and negative pressure should be maintained in bathrooms.

④The front hall of the restaurant should maintain positive pressure, and the kitchen should maintain negative pressure. The air pressure in the restaurant should be between the front room and the kitchen.

25. The layout principles of air ducts in the suspended ceiling: from top to bottom: smoke exhaust duct, exhaust duct, air supply duct, and water pipe.

26. The relative positions of the air supply and exhaust outlets

When the air supply and exhaust ducts are parallel to the air-conditioned room, try not to arrange the air supply and exhaust outlets side by side, and it is best to arrange them in a staggered manner.

27. The design of the air supply duct

Try to prevent the air from flowing backward in the air supply duct to ensure good air flow and air outlet effect in the pipe.

28. The overlap between the tee and the air duct

The diameter of the pipe connected to the tee should be consistent with the diameter of the tee. Do not change the diameter to avoid excessive local losses.

About ventilation, smoke exhaust and smoke prevention

1. Determination of ventilation times to eliminate residual heat and moisture.

① The fire pump room shall not be less than 8 times/h;

② The transformer room shall be 10 times/h.

2． Smoke exhaust is mainly for underground garages, rooms with an area of ??more than 100m2 and no external windows, inner walkways, atriums and basements with an area of ??more than 50m2.

①For detailed calculation of smoke emission, please refer to the "Fire Protection Design Code for High-rise Civil Buildings"

3. Smoke prevention

It mainly provides pressurized air supply to the smoke-proof stairwell and fire elevator front room (shared front room).

①For the calculation of air volume, please refer to the "Fire Protection Design Code for High-rise Civil Buildings".

② Air vents must be installed in the front room of the fire elevator (common front room). Multi-leaf air vents must be installed on each floor. Smoke-proof stairwells can be equipped with self-hanging louvered air vents on each floor.

In addition, natural smoke exhaust can also be used, that is, if there is an external window and the openable area of ??the external window meets certain requirements, mechanical smoke prevention is not needed.

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