【 Weak current College 】 on HVAC design design issues

Summary-control on the design specifications, regulations, standards, listed the HVAC system design, equipment selection, network layout, graphics, and other aspects of typical problems, analyses the causes of the problem, the proposed solutions and measures for improvement.

As a result of work relations, access to some of the design of HVAC project design, control of the heating, ventilation and air conditioning design code GBJ19-87 (hereinafter referred to as the "design specifications"), the senior civil building design fire protection standard "GB50045-95 (hereinafter referred to as the" regulations "), the heating, ventilation and air conditioning cartography standards GBJ114-88 (hereinafter referred to as the" cartography standards "), the building design documentation of the depth of the regulations (hereinafter referred to as the" design depth regulations ") and other relevant norms, rules, standards, find HVAC design staff in implementing the existing norms, regulations, standards, systems design, equipment selection, network layout, there is a lot of problems. Now will see problems and their causes and solutions of the following.

1 implement HVAC design specifications and standards issues

1.1 indoor and outdoor air calculation parameters do not meet standard requirements
The design code provides that the calculation of indoor air in winter, bathroom, toilet parameter should not be lower than 12 ° c, bathroom should not be less than 25 degrees centigrade. However, some public buildings of toilet, lavatory room (equipped with exterior Windows, facades), residential building of the bathroom (in winter there is a bath of hot water supply, should be treated as bathroom) is not set heat sink, it is difficult to reach room temperature not lower than 12 ° c and 25 ° c. There is also a kitchen of the apartment building is located the heatsink, I think that is wrong, kitchen and interior temperature also should be not less than 12 degrees centigrade requirements set heat sink.
The design code provisions, some of the major cities of outdoor weather parameter should be the norm in Appendix II. According to the Appendix b, Beijing area outdoor design temperature in winter heating except yanqing, Miyun, should be-9 ° c. While project is located in the Beijing suburbs, has access to-12 ° c, is obviously not appropriate.

1.2 heating load calculation leaky and wrong entries
The design code provisions, winter heating system heat load should include heated indoor door slot into the cold air of the heat consumption. But some of the projects in the calculation of the heating load calculation that partly not heat loss, resulting in the heating of heat load and from larger; the design specifications "on the envelope's heat loss calculation orientation correction rate made clear, 0 ~ 10% in the North, East and West-5 per cent, South-15% ~ 30%, but some projects will become the orientation correction rate of 20% in the North, East, West, South, 15%-5%, contrary to the specification requirements.

1.3 bathroom radiator type selection wrong
The design code requirements, relative humidity larger room use cast iron radiators. However, many works of the toilet using steel radiator, nor the strengthening of protection measures, it is inappropriate. I have seen some of the Office building of the toilet using steel closed radiator, but I couldn't use a few years, the radiator series Tablet is corrupted, the remaining two tubes are also serious corrosion. Practice has proved that such places the best use of cast iron radiators or aluminum radiator.

1.4 staircase radiators, pipes are not separate configuration
The design code provisions, stairs or other places where freezing danger, their radiator should be separate legislation, the branch pipe heating, and shall not be equipped with control valve. However, some projects will staircase radiator and radiator adjacent room heating rooms sharing a standpipe, dual side connection, connecting staircases one side of the radiator, the other connection o room room radiator and radiator pipes on the valve. In this way, because it is difficult to guarantee enclosed stairs, once the heating failure, may affect adjacent room heating effect, even crack the heatsink.

1.5 heating pipe laying slope does not conform to specification
The design code requirements, installation of heating pipes should have certain slope, for hot water pipe slope use 0.003, shall not be less than 0.002. However, some engineering heating for return pipe slope only 0.001 ~ 0.0015. Of course, if there were constraints, hot water pipes or even no gradient, but this time for laying should ensure the water flow in pipes must not be less than the 0.25m/s.

1.6 kitchen operations room ventilation problems
The diet building design code (JGJ64-89) on kitchen operations room ventilation was clearly defined: (1) calculation of the exhaust volume of 65% by exhaust hood flows into the outdoors, but the room ventilation exhaust of a full 35%; (2) exhaust hood mouth suction speed generally should not be less than 0.5m/s, exhaust tube speed should not be less than 10m/s; (3) should be heated up air flow between the exhaust volume of 70%, the room should not be greater than the negative pressure values 5Pa. However, there are works of kitchen exhaust hood is not set, only the walls located several pieces of the exhaust fan; though set exhaust hood, but cover mouth suction speed far less than 0.5m/s, with optional blower air volume is low. Most of the works does not set the overall ventilation device, also does not take into account wind installations, difficult to maintain indoor health environmental requirements and negative pressure values.

1.7 expansion tank and thermal (cold) water system does not meet the standard requirements
The boiler room design code (GB50041-92) provides that high expansion tanks and hot-water system pipe should not be fitted with valves. The pipe is a pipe expansion pipe and circulation. This article on chilled water system is applicable. But some of the chilled water system expansion of high-expansion tank fittings to the frozen water on the room set and installed valve, which is not allowed. Once the operation errors, will compromise system security.

1.8 fire ventilation and air-conditioning system valve settings do not meet standard requirements
The doctrine of the duct is not appropriate to pass through the firewall or deformation seams, as must pass through, should pass through the firewall set fire dampers; through the deformational slots, should set the fire damper on both sides. However, some tall buildings, windPipe through the firewall is not set fire dampers, air ducts only through the deformational slots in the side of a fire safety valve, and the other side it is not set. In addition, some engineering fire damper position is set incorrectly. According to the requirements of fire safety valve should close the firewall settings, and connect the fire damper of through-wall air pipe thickness ≥ 1.6mm δ, firewalls on both sides from 2m range air pipe should be non-combustible materials and thermal insulation. But some engineering ventilation and air-conditioning duct on the fire damper setting, away from the firewall at will, during which wind pipe is neither marked thickening, nor take any protection measures that exist.

1.9 smoke staircase in front of the room air flow by identify the problem
The resistance of the law on high-rise building smoke stairs before pressurization provides air volume, and points to the specific air flow value. In the notes to that article to open door through the door of the wind speed is less than 0.7m/s; provisions provided in the notes to the door opening number, 20-2, the following 20 layers above is 3. The regulations also stipulate that the smoke before the Chamber of the stairwell pressurizationoutlet should have one on each floor. Under these provisions, the layers can be projected from in front of room air in air should be L/2 (20 stories) or L/3 (20 layers above, L-front room total pressure air). However, there are works whose smoke stairs room air air volume is labeled L/n (where n is the number of building layer), it is clear that small. As a 12-story building, smoke stairs before the total pressure air as 16000m3/h, but each layer front room air flow is labeled 16000/12 ≈ 1300 (m3/h), it is clear that its air inlet with small. The correct dimension should be 16000/2 = 8000 (m3/h), should this configuration outlet size.

1.10 wrongly smoke partition exhaust volume calculation does not get to the calculation of the exhaust fan
The doctrine of the exhaust fan was clearly defined: take a smoke partition exhaust, should press the smoke partition area is not less per m2 60m3/h, with two or more smoke partition exhaust, the maximum preventing smoke partition area is not less per m2 120m3/h. Please note, here is a selection of the air exhaust fan, and not the smoke partition exhaust volume doubles (on each smoke partition exhaust volume still press the smoke partition area is not less per m2 60m3/h), but when the exhaust fan either horizontally or vertically with two or more exhaust smoke partition, only two exhaust smoke partition at the same time to determine the exhaust fan of the air flow.

However, some project exhaust fan horizontal shoulder area of size 2 ~ 3 exhaust smoke partitions, design errors, the exhaust fan of 2 ~ 3 smoke partition is not less per m2 approx. 60m3/h calculation, instead of by one of the biggest smoke partition area is not less per m2 120m3/h, causing the exhaust fan is small, it is difficult to meet fire protection requirements. There is also the exhaust fan (systems) in vertical orientation with two or more smoke partition (aisle) exhaust, design errors will each smoke partition (aisle) exhaust volume accordingto the respective area is not less per m2 120m3/h calculation, instead of by their respective area of not less than per m2 60m3/h calculated, multiplying the vertical smoke partition (aisle) exhaust volume more than doubled, making each floor duct, Tuyere configured on the high side.

1.11 high-rise building exhaust system improperly exhaust port selection
The provisions of the regulations, (HVAC) ducts pass through fire partition wall Department
Should be set fire damper. The author believes that the exhaust air pipe should not pass through the firewall, such as the need to go through, you should put the firewall is set when the gas temperature of more than 280 ° c will automatically close when the fire damper, and exhaust fan interlock. However, some project at design time on this negligence. If a basement an exhaust system with 3 bedrooms and 1 internal walkways (all rooms and corridors between doors are fireproof door) of smoke, smoke exhaust duct with a smoke fire dampers, while all rooms and corridors of the exhaust vents are single louver, exhaust pipe passes through the firewall is not set up smoke fire dampers. This problem is caused by: each room fire door useless, once a room fire, through the exhaust pipe affecting other rooms. The correct approach is: in single-layer blinds exhaust mouth (exhaust duct through firewall) additional smoke fire dampers (280 ° c auto-off) or will be changed to single-layer louver dedicated exhaust outlet (usually the normally closed, open automatically when the ignition, the exhaust gas back off 280 ° c).

2 in engineering design problems

2.1 excessive heating portal settings
When setting the heating, both entrances to consider the reasonableness of indoor heating system, and to consider the reasonableness of the outdoor pipelines linking, not only figure indoor system design is convenient, easy, regardless of the outdoor pipe network system. However, some engineering heating too many entrances. In the case of a 7 storey building, indoor heating system is divided into 10 loops (1 ~ 2-4, 3-7-6), heating entrances are also up to 10 more points of convergence with an outside line, too many have several directions, not only to get an outside line construction caused trouble, also for future inconvenience indoor system regulation.

2.2 heating system design is not reasonable
Heating system design unreasonable: ① the heating system consists of: 1 Master Li (stem)-introduction, several loop, loop, no valves, to the system operation, maintenance and management. ② the heating pipe layout is reasonable, and not easy to coordinate construction professional, or heating riser directly in the window, use, and affects both unsightly; or heating in horizontal pipe laying in channels, affecting both on the ground, he is not in a position to walk belongings. ③ the supply and return water dry pipe set high point leakage, once the exhaust gas, difficult to eliminate, the impact of system use. ④ the heating system for the same program, a loop fare for Chang 300m, cause, backwater dry pipe slope is very difficult to meet the specifications provided for not less than 0.002 requirements. ⑤ the heating system for two-sided thermal load on both sides of the connection, and the quantity of heat sink, vastlyWhile the two radiator supply and return water pipes has access to both sides of the same diameter, hydraulic imbalance, it is difficult to be allocated according to the design flow.

2.3 exhaust system design is not reasonable
If a dark basement toilet (WC) and several domestic room and equipment rooms located a ventilation system, horizontal duct length 60m, section only larger 200mm×200mm, wind resistance; select a roof fan exhaust, but the fan installed in the walls, were not coordinated. There are also located in the basement of the works of several private rooms (both darkroom), all rooms have a ceiling fan, air exhaust through dozens of m-long horizontal wind pipe from the outside, the air pipe section only 150mm×150mm, resistance, poor ventilation effect.

2.4 air-conditioning system choice unreasonable
If a project has a commanding Hall, conference rooms, computer rooms, etc., this nature House, ideal for air conditioning system should be a low-speed air duct system, and designed it with fan-coil system, and not set fresh air supply system, it is clearly unreasonable. As a project owner requirements section of the room interior design parameters for: winter tn = 18 ~ 22 ° c, φ = 55% ± 5%, summer tn = 25 ~ 26 ℃, φ = 60% ± 5%; other room tn = 22 ± 2 ° c, φ = 40% ~ 60%, the level of clean level is less than 10000, fresh air, 40 ~ 60m3/(h · people). The nature of these two types of rooms, all designed with fan-coil system, and not set fresh air supply system. Such a system cannot satisfy the request of the party.

2.5 toilet with air blower plate Tube is not fresh
The toilet has to meet the temperature requirements, and to eliminate odour, guarantee hygienic requirements. However, there is a project of the toilet without exhaust and no fresh air supply, simple horizontal dark dress fan coil for cooling, heating, causing odour itself cycle, it is inappropriate.

2.6 balance valve settings and aperture selection problems
Chilled water system should set balance valve, should generally be set on the return pipe. But some engineering air supply unit chilled water supply and return pipe has set the aperture and the diameter of the same valve. The author believes that the water supply pipe on does not have to set the balance valve, only set on the return pipe. Balancing valve diameter should be determined through the check calculation.
3 design drawings problems

3.1 design description incomplete
The design depth of regulations on HVAC design descriptions should include content clearly. Design description should have indoor and outdoor design parameters; heat and cold sources; htm, refrigerant parameters; heat load and heat consumption indicators system total resistance; radiator models; air-conditioning cooling load, thermal load; system forms and controls methods; noise, vibration isolation, fire prevention, corrosion resistance, thermal insulation; air duct, pipe material selection, installation requirements; system pressure test requirements. However, some design Notes content is incomplete.

3.2 plan enough depth, some should be drawn content omissions
The design depth of regulations on HVAC plan to indicate the detailed provisions. However, a considerable number of engineering design is not fully complying with the provisions in drawing, the main problems are: heating floor plan, some not tagging level dry pipe diameter and position size; there is no number of standpipe; some have labeled risers, but will stand pipe leak painting; a second layer to the top level and draw the floor plan, radiator also conducted a callout, hierarchy but does not indicate the appropriate level; only with the first floor heating surface, without drawing on the second floor to top floor heating plane. Ventilation and air conditioning plan, some did not indicate the number and positioning of various equipment dimensions; outstanding description of freezing water pipe diameter and position size. There is also the design of public buildings, the kitchen part of heating, ventilation, air conditioning, and other content for kitchen equipment manufacturers to do it, it is not appropriate.

3.3 system map depth not enough
The design depth of regulations on HVAC system diagram rendering explicit requirements. But some of the engineering design for failing to comply with the prescribed execution. The main problems are: heating system diagram, there is no number of risers, but to the axis, instead of building; a pipe, note the grade, slope, but did not indicate the beginning or end of pipeline end elevation; some changes in the pipeline (steering) elevationleakage note; some even not art heating system diagram or riser diagram. Air conditioning, ventilation design, and some projects did not draw a chilled water system diagram and system diagrams (if the floor plan fully explain clearly, can not draw a system diagram, but for some of the more complex design of ventilation and air conditioning, rely on the floor plan is difficult to express clearly).

3.4 boiler room design simplistic
The design depth of regulations on boiler house construction drawing design for detailed provisions. However, the boiler room design, drew a plan only, no profiles and system diagrams, many should explain the content is not accounted for, from the design depth requires very different.

3.5 account book content is not full or even all blank
The design depth of regulations on HVAC design account book shall include the detail of the content. However, a significant part of the engineering design no HVAC design account book. Some heating air-conditioning design notwithstanding the account book, but the content is incomplete. The design of heating, heat loss calculation, only without the hydraulic balance calculations and calculation; a radiator of high-rise buildings of central air-conditioning and smoke control design, only the summer cooling load calculation, without air-conditioning system and water system hydraulic calculation, no refrigeration and air conditioning equipment selection calculation, calculation of smoke-free. There's air conditioning design, regardless of room size, direction, level, location (intermediate or end) are the same indicators to estimate the summer air conditioning air-conditioning cooling load and thermal load in winter, and to configure the air conditioning equipment, this is inappropriate.

3.6 HVAC equipment is not numbered list indicated that the picture not complicated
The drawing standards stipulates that the heating, ventilation and air conditioning equipment, components, parts,preferably numbered list indicated that their models, performance should be complete, clear the form, only specify their drawings. However, HVAC design did not press thisProvisions, but to all kinds of equipment, parts of the name, model, or are written on the surface, surface text complexity, both fees Kung Fu, note write incomplete, unclear.

3.7 floor plans, elevations, system diagrams are not consistent
HVAC design, flat, profiles and system diagrams corresponding parts of the equipment, size, and other content should be consistent, otherwise to construction and installation, use and management. But some heating design, number, floor plan and the radiator system diagrams are not consistent; supply and return water dry pipe diameter, floor plan and system diagrams are not consistent; pipe connections, floor plan and system diagrams are not consistent. There is air conditioning and ventilation design, duct sizing, layout and system diagrams are not consistent; equipment, parts, location plan and profile, the dimensions are not consistent; the device number, quantity, drawings are not consistent with the device table; air-conditioning design selection of air conditioning and refrigeration equipment models, floor plans, systems and equipment table note write not one, people do.

3.8 design drawings and calculation of book inconsistencies
HVAC design, all equipment, pipes, part of select are determined by calculation, in a sense, design drawings, is the embodiment of computing books, so the design drawings and calculation should be identical. But the number of heating design, radiator, dry pipe diameter, design drawings and calculation of books are not consistent, or even considerably, account book no, drawing on, account book in small, drawing on the zoomed in, account book big, in drawings narrows. Calculation is completed, the drawings found unreasonable, allow adjustment, but should be adjusted calculation of books or adjust the description, thedrawings and calculation of the final book.

4 the cause and solution

4.1 on existing design rules, regulations, standards, learning is not enough, not enough to implement and therefore should strengthen the existing design rules, regulations, standards of learning, improve the implementation of the design specification.

4.2 design process lack technical and economical comparison of multiple scenarios, randomness. Should be the same as in architectural design, a number of programmes, reasonable design.

4.3 drawing review is not strict, or even mere formalities. Should insist triple (since the audit, audit, examination) system to ensure that design (including drawings, account book) quality, eliminate errors.

5 reference documents
1 Beijing General Research Institute for Nonferrous metallurgy design-heating, ventilation and air conditioning design specification (GBJ19-87): zhongguojihuachubanshe, 1988.
2 China Academy of building energy-saving design civilian standards (existing building) (GBJ26-95)-Beijing: the Chinese construction industry press, 1996.
3 Chinese architecture design Institute, Liaoning province of Northeast China food safety control and inspection the diet building design standard. (JGJ64-89)-Beijing: the Chinese construction industry press, 1990.
4 mechanical electronic industry code for design-boiler room (GB50041-92): zhongguojihuachubanshe, 1993.
5 the Ministry of public security. high-rise residential building design fire protection standard (GB50045-95): zhongguojihuachubanshe, 1995.
6 China Research Institute of building standard design-heating, ventilation and air conditioning drawing standards (GBJ114-88): zhongguojihuachubanshe, 1995.
7 zhongnan Institute. architectural engineering design documentation depth requirement. South Africa Institute, 1992.