Heating ventilation and air conditioning systems

Control systems are devised to suit each individual application. Generally, each part of the system will contain air of different types. With reference to Fig. 27.6 the room air (RA) is extracted by a fan, a proportion of the air is exhausted to atmosphere and the remainder

Note. This diagram forms an introduction to the basic system concept highlighting the major functional areas of the overall system. It is intended for users who require a basic appreciation of the system.

240 V 50 Hz

N .

Note. This diagram forms an introduction to the basic system concept highlighting the major functional areas of the overall system. It is intended for users who require a basic appreciation of the system.

(a) Block diagram

Thyristor control unit PL1 A

(a) Block diagram

Thyristor control unit PL1 A

Lthw Boiler House Layout

Note. This diagram shows part of a detailed block diagram developed At this level the diagram becomes a useful diagnostic tool where input/

from the simple form of block diagram shown in (a). In this diagram functional information has been expanded and specific information in respect of input/output terminations has been added.

output parameters may be monitored and hence faulty operation detected at unit, printed boards, etc. level. Maintenance at this level involves the replacement of the faulty unit or printed circuit board thus restoring normal working fairly rapidly.

Note. This diagram shows part of a detailed block diagram developed At this level the diagram becomes a useful diagnostic tool where input/

from the simple form of block diagram shown in (a). In this diagram functional information has been expanded and specific information in respect of input/output terminations has been added.

(b) Detailed block diagram output parameters may be monitored and hence faulty operation detected at unit, printed boards, etc. level. Maintenance at this level involves the replacement of the faulty unit or printed circuit board thus restoring normal working fairly rapidly.

Squarers

Air Conditioner Block Diagram Circuit Engineering Drawing Block Unit

boards forming part of the overall thyrlstor control system. Functional stage headings and waveforms have been Included to assist the reader In: (i) understanding the function of the equipment; (Ii) rapid location of areas of malfunction. (Ml) Circuit diagram for zero voltage trigger

50HZ input at TR1 and TR3

TR1 output

50HZ input at TR1 and TR3

TR1 output

C4, R6, output l I \ j ¡i (Differentiator)_|V_j_ iv j

TR2 output

C4, R6, output l I \ j ¡i (Differentiator)_|V_j_ iv j

TR3 output

C3, R7, output (Differentiator)

TR4 input TR5 output

inrrrr

Note. Although the waveforms shown in (c) are of assistance to the reader in establishing that the correct signals are present at various parts of the diagram, thus assisting preliminary fault location, it does not show the timing relationship that exists between waveforms. This diagram is a supplementary diagram that defines this time relationship.

(d) Supplementary diagram for waveform development for zerovoltage trigger

Fig. 27.2 (continued)

is returned and mixed with a supply of fresh outside air. The mixed air will then be returned to the room via a supply air fan after its temperature has been corrected to suit the design requirements.

In most cases this involves a heating operation. However, if the outside air temperature is high, or if there are considerable heat gains within the controlled space, then a cooling operation may well be necessary. In addition, full air conditioning specifications require control of the relative humidity in the space.

Personal physical comfort conditions depend on adjusting air and surface temperatures, humidity and air movement. By balancing these four factors, the engineer can design a climate to suit any type of activity.

In Fig. 27.6 the air is heated by passage through a heat exchanger supplied with hot water. Hot water from a boiler operating at normal atmospheric pressure is Low Temperature Hot Water (LTHW). If the boiler operates at pressure, its output is High Temperature Hot Water (HTHW). The heat exchanger could also be supplied with steam or operated by electricity.

The volume of outside air supplied will vary considerably with the occupancy density within the space and the activity. For example, theatres, public houses, conference rooms, areas with large solar heat gains, industrial premises with processing equipment, swimming pools and incubators, to name just a few, all require very special attention. Hence, various degrees of air purification and levels of sophistication exist. Three typical schemes now follow and Fig. 27.7 shows a ventilation system. Here a controller adjusts the position of a three way valve so that more, or less, water passes through the heat exchanger in response to supply air temperature demands. The air supplies are controlled by electrically operated dampers fitted in the ducts. Note that the air into the space has its temperature measured by the sensor f1. An alternative position for the sensor could be in the outlet duct when it could take note of any temperature increases generated within the space, or it could be positioned within the space itself, shown by u2. Many choices need to be considered.

A scheme for partial air conditioning is illustrated in Fig. 27.8 where in addition to ventilation and heating, the humidity has been given a degree of control. For full air conditioning it is necessary to provide equipment to cool the air and typical plant has been added to the layout in Fig. 27.9.

All of the installed plant needs to be carefully sized to ensure that specifications for air quality are met. The Engineer uses a psychrometric chart to determine the physical properties of the air to be handled.

F25 Pic Fuse Box

j R9C F25 I Fuse/relay box "2ök

Dim light relay

54-73A

Ci22 2.5 BK/OG

j R9C F25 I Fuse/relay box "2ök

Ignition switch

15-16

2.5 BK/SR

-fe.

15-B

4 BK

4 BK

i5-F

4 BK

i5-i9

Dim light relay

54-73A

fS2 Earth distribution C9.CC

54-96

Ci22 2.5 BK/OG

Ria dim light resistor

(a) Headlamps 32.CC-Ci (Ford Motor Co. System).

T"

i5-ia

9 i5

Rower distribution

C7.CC

Light/Wiper I switch

56-i

(2) Dipped beam

1 R9C

Fuse/relay box

F23 i5k

Fuse details Ca.CC

I Fuse details I Ca.CC

56B-i6

75 YE C121

56A-3

Multi-function switch w I (i) Flash i 2"3 | (2) Dip (3) Main

Ci6C

CC-C2

56A-16

Dipped beam relay

C121

Earth

5 YE/BU I distribution C9.CC

32.CC-C2

GiCCi

32.00-00 32.00-01

32.00-00 32.00-01

1 P90 Fuse/relay box

1 P90 Fuse/relay box

N13 Instrument Cluster Fuse

Instrument cluster

Earth distribution 09.00

Earth distribution 09.00

Earth distribution 09.00

Instrument cluster

G1001

F15 10A

I Fuse details ¡08.00

Instrument cluster (4) Direction indicator

49A-1

C336 .75 BK/WH/GN

49A-1

Instrument cluster (4) Direction indicator

C336 .75 BK/WH/GN

work technograph

32.40-00

Indicator flasher relay

E4 light

C49 f S3

Earth distribution 09.00

52 Clhjd>

Earth distribution 09.00

49A-1

F17 10A

52 Clhjd>

49A-1

Headlamps 32.00

Earth distribution 09.00

Nissan N13 Headlamp Wiring

Headlamps 32.00

Horn 32.70

Headlamps 32.00

F19 10A

Fuse/relay box

Headlamps 32.00

Headlamps 32.00

Multi-function switch

(4) Hazard flesher warning light on

(5) RH direction indicator

(6) RH direction 2.5 WH indicator

Horn 32.70

Headlamps 32.00

32.40-01

32.40-02

(c) Signal and hazard indicators 32.40-00.

Fuse details 08.00

54-33

54-33

Heating And Ventilation Engineer

Fuse details 08.00

Fuse/relay box

Windscreen washer pump

Distribution 09.00

K11 Front intermittent wiper relay

1 distribution

09.00

I distribution 09.00

Fuse/relay box

Windscreen washer pump

Light/wiper switch

(3) Normal speed

(4) Fast speed

(7) Intermittent wipe

(8) Windscreen washer/ headlamp washer

Distribution 09.00

K11 Front intermittent wiper relay

1 distribution

09.00

I distribution 09.00

G1001

(d) Wiper/washer control 32.60-01.

Component location views

Component location views

Engineering Drawing Conventions
Behind dash (LH drive shown, RH drive similar)

A2 Instrument cluster D1

C3 D1

C105a

C105b

E4 Trailer warning light .

G1001

M3 Heater blower

. D1 . E2 . C4 . D3 .A4 . E1 . B4 . E4 . C4 . D1 . E1 . C4 . D4 . A3 . F4 . E1 . E4 . E2

N13 Electrical headlamp alignment

system switch E1

N14 Heater blower switch D3

N15 Stop light switch D1

N16 Safety switch D1

N26 Door ajar sensor, driver side A3

51 0 B4

511 B4

51 2 E4

51 3 E4

S18 B4

N3 Door ajar sensor, passenger side F4

Fig. 27.4 Component location views 90.10-22

C107

58-26 SR/BU

30-66 RD/YE

31-49 BN

56B-4 YE/WH

58-26 SR/BU

30-66 RD/YE

31-49 BN

C110

58-20M SR/GN

31-117 BN

C111

Connector views

56B 1B YE/BK 56B-18A YE/WH 31-98B BN

56B-9 YE/SR 56B-18 YE/WH 31-98A BN

C120

C121

C122

54-54A BK/OG 30-41 RD/WH

30-40 RD/YE

31-113 BN

C123

56B-16 YE

54-96 BK/GN + 56B-15 YE/BU [54-99 BK/GN+ 56B-15 YE/BU]

15-19 BK/YE

C126

C122

54-73 BK/OG

54-72 BK/RD 31-89 BN

C128

31B-26 BN/RD 31B-28 BN/YE

31B-27 BN/BU

58-34 SR/BU

54-73 BK/OG

54-72 BK/RD 31-89 BN

31B-26 BN/RD 31B-28 BN/YE

31B-27 BN/BU

C129

54-12 BU/GN

54-12 BU/GN

54-12 BU/GN

54-12 BU/GN

Fig. 27.5 Connector view 91.00-05

Air types: (DIN 1946).

Air type

Abbreviation

Outside air

AU

Penetrated outside air

VAU

Exhaust air

FO

Aftertreated exhaust air

NFO

Extract air

AB

Room air

RA

Aftertreated extract air

NAB

Return air

UM

Mixed air

MI

Supply air

ZU

Pretreated supply air

VZU

Water:

Flow

V

Return

R

Hthw Schematic
-15 -10 -5 0 5 10 15 20 25 30 35 40

Fig. 27.7 Ventilation system diagram. System designed to control the temperature of supply air into a space with heating from LTHW, HTHW or a steam heated coil. Variant with remote setpoint potentiometer s2

-15 -10 -5 0 5 10 15 20 25 30 35 40

Controller output temperature

Controller output humidity

Setpoint curve tR[°C]

Setpoint curve

Fig. 27.8 Partial air conditioning system. System designed to control the extract air from a room. The air into the space is heated with an electric heating coil and humidified with steam. Alternative: Room sensor instead of extract air sensor. Variant: with low limit supply air temperature control, and high limit supply air humidity control

ICrH

Control Temperature Humidity Scheme

Fig. 27.9 Air conditioning system diagram. System designed to control the extract air from a room. The air into the space is heated by LTHW, HTHW or a steam heated coil. Cooling and dehumidifying with CHW cooling coil. Humidifying with steam. Alternative: Room sensor instead of extract air sensor. Variants: with low limit supply air temperature control, and with summer compensation

Fig. 27.9 Air conditioning system diagram. System designed to control the extract air from a room. The air into the space is heated by LTHW, HTHW or a steam heated coil. Cooling and dehumidifying with CHW cooling coil. Humidifying with steam. Alternative: Room sensor instead of extract air sensor. Variants: with low limit supply air temperature control, and with summer compensation

Functions

Temperature control

The duct sensor f1 measures the temperature tzu. The controller u1 compares this value with the selected setpoint XK on the controller u1 or on the remote setpoint potentiometer u2 and adjusts the heating coil valve s1 in accordance with the difference between the two.

Safety devices

When there is danger of frost, the frost protection thermostat f2 must switch off the fan, close the damper s2, open the heating coil valve s1 and, where appropriate, switch on the heating pump.

Controller output temperature

Controller output temperature

Functions

Temperature control

The duct sensor f1 or the room sensor f2 measures the temperature tR. The controller u1 compares this value with the selected setpoint XK and adjusts the heating coil step controller (or power controller) u2 in accordance with the difference between the two.

Humidity control

The duct sensor f1 or the room sensor f2 measures the humidity q>R. The controller u3 compares this value with the selected setpoint XK and adjusts the humidfying valve s1 in accordance with the difference between the two.

Safety devices

If there is an air flow failure, the differential presure switch f4 must cut off the control voltage of the electric heating coil. With electric heating coils, it is advisable to incorporate a timer so that the fan will run on for approximately 5 min and dissipate any residual heat.

Functions

Temperature control

The duct sensor f1 or the room sensor f2 measures the temperature tR. The controller u1 compares this value with the selected setpoint XK and adjusts the heating coil valve si or the cooling coil valve s2 in sequence in accordance with the difference between the two.

Humidity control

The duct sensor f1 or the room sensor f2 measures the humidity q>R. The controller u2 compares this value with the selected setpoint XK and adjusts the humidfying value s3 or the cooling valve s2 in sequence in accordance with the difference bentween the two.

Safety devices

When there is danger of frost, the frost protection thermostat f4 must switch off the fan, close the damper s4, open the heating coil valve s1 and, where appropriate, switch on the heating pump.

Variant: with low limit supply air temperature control

The low limit supply air temperature sensor f3 prevents the supply air temperature tzu from dropping below the cut-in point XE set on the controller ul (draught elimination).

Variant: with summer compensation.

The outside temperature compensation sensor u3 is used to increase the room temperature tR in summer. If the outside temperatue ta rises above the cut-in point XE (22°C), the setpoint XK is increased continuously by the selected steepness SS.

Engineer uses a psychrometric chart to determine the physical properties of the air to be handled.

Controller output temperature

Controller output humidity

Setpoint curve tR[0C]

Setpoint curve tR[0C]

uy^ss

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