Transcript
-SQA-SCOTTISH QUALIFICATIONS AUTHORITY Hanover House 24 Douglas Street GLASGOW G2 7NG NATIONAL CERTIFICATE MODULE DESCRIPTOR -Module Number-
0075043
-Session-1987-88
-Superclass-
TH
-Title-
DOMESTIC GAS FIRED CENTRAL HEATING
-DESCRIPTIONType and Purpose
Preferred Entry Level
Learning Outcomes
A specialist module to give technician level students on courses specifically related to or allied with the utilisation and/or distribution of natural gas an understanding of wet central heating and warm air central heating gas appliances, controls, systems and design procedures.
75042 Domestic Gas Appliances
The student should: 1.
know the construction, operation and application of domestic gas fired central heating appliances;
2.
know the operation and function of controls for a gas fired central heating system;
3.
know the pipe and ducting systems used to provide combined central heating and domestic hot water supplies;
4.
know the sequence of controls for central heating systems;
5.
know and apply design procedures for gas fired central heating systems suitable for small domestic buildings.
Continuation of Module No. 75043 Content/ Context
Session 1987-88
Corresponding to Learning Outcomes 1-5: 1.
the construction, operation and application of: (a)
wet central heating appliances: (i) (ii) (iii) (iv)
(b)
cast iron sectional; low water content; combination; condensing.
warm air central heating appliances: (i) (ii) (iii) (iv) (v)
2.
3.
upflow; downflow; crossflow; direct heat exchanger; indirect heat exchanger.
(a)
the operation of the primary gas controls manual control, governor, flame failure device, boiler thermostat;
(b)
the operation and function of electronic and electro mechanical secondary controls: (i)
clocks and programmers, room and cylinder thermostats motorised zone valves;
(ii)
unit control switch, limit thermostat;
(a)
Combined central heating and domestic hot water systems:- heating systems-small bore and micro bore; hot water systems - gravity circulation and pumped circulation;
(b)
warm air central heating systems eg. (i)
extended plenum;
(ii) radial; (iii) subduct;
4.
the operational sequence of controls for central heating systems. Use of functional flow and schematic diagrams for fault finding.
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Continuation of Module No. 75043 5.
Session 1987-88
heat requirements; pipe and radiator sizing; duct sizing; pipe and duct routes.
Suggested Learning and Teaching Approaches
Extensive use of gas appliances and controls is essential to this module. Where appropriate student participation in the demonstration of equipment under supervision is highly desirable. Project work should be included as part of the ongoing assessment for Learning Outcome 5. Learning outcomes 1 - 5 may be monitored by tutorials and student centred learning.
Assessment Procedures
Acceptable performance in the module will be satisfactory achievement of the performance criteria for each learning outcome. Where cutting scores are stated these are intended to be for guidance. The precise cutting score for a test will depend on the difficulty of the test and will have to be decided by the Tutor aided by the Assessor. The following abbreviations are used below: LO IA PC
Learning Outcome Instrument of Assessment Performance Criteria
LO1 IA
6 written short answer questions 4 of which include graphics:
(a)
two questions with graphics relating to wet central heating appliances;
(b)
two questions with graphics relating to dry central heating appliances;
(c)
two questions relating to the application of central heating appliances (ie wet and dry).
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Continuation of Module No. 75043
Session 1987-88
PC In (a) and (b) the performance criteria will rely on the accuracy of descriptions and sketches: (a)
for two from the following list of wet central heating boilers: (i) (ii) (iii) (iv)
cast iron sectional; low water content; combination; condensing.
the construction detail and operation will be described and illustrated by an annotated sketch. The points of construction to be indicated are burner, combustion chamber, heat exchanger flue way. Flow of air for combustion and products of combustion. (b)
For two from the following list of warm air central heating units: (i) (ii) (iii) (iv) (v)
upflow; downflow; crossflow; direct heat exchanger; indirect heat exchanger.
the construction and operation will be described and illustrated by an annotated sketch. The points of construction to be indicated are burner combustion chamber heat exchanger fan flue way. Flow of air for combustion, flow of products of combustion, flow of heated air. (c)
One question for each of: (i) (ii)
wet central heating boiler; warm air central heating unit.
Each answer to indicate how the distinguishing characteristics of each type of boiler would be applied in practice so that the engineer can select the appropriate appliance for a particular installation. For example: cast iron section traditional heavy boiler high thermal efficiency; low water content - light weight suitable for wall -4 -
Continuation of Module No. 75043
Session 1987-88
mounting. combination - application of sealed central heating system; condensing - new design with exceptionally high thermal efficiency; Warm air - upflow, downflow and crossflow the relationship of burner heat exchanger and fan determining the type of flow and how these can be applied to installations. Direct heat exchanger - hot gases heat the metal heat exchanger. Indirect heat exchanger previously heated water heats the heat exchanger. LO2 IA
8 written short answer questions and graphic exercises. (a)
4 questions which relate to primary controls;
(b)
4 questions which relate to electronic and electro mechanical secondary controls.
In each case the graphics exercise is to complete a sketch. PC In (a) and (b) the performance criteria will rely on the accuracy of description and sketching: (a)
clearly describe, with the aid of the sketch, the operation and function of each of the following primary controls: (i) (ii) (iii) (iv)
(b)
manual control; constant pressure governor; flame failure device; boiler thermostat.
clearly describe, with aid of the sketch, the operation and function of each of the following primary controls: (I)
clock and programmer;
(ii)
room and cylinder thermostats;
(iii)
zone valves;
(iv)
fan control switch and limit thermostat .
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Continuation of Module No. 75043
Session 1987-88
LO3 IA
5 graphics exercises where the student - completes a worksheet and annotates the five incomplete sketches of which: 1 question is on a small bore central heating and domestic hot water system. 1 question on a microbore central heating system 1 question on a sealed central heating system 2 questions on ducted warm air systems.
PC In each case the question will be marked on accuracy of sketching and use of the correct terminology. (a)
correct pipework layout and location of pump to supply water to radiators and a calorifier to provide domestic hot water.
(b)
correct pipework layout indicating the use of a manifold, microbore, piping, twin entry radiator valves.
(c)
correct pipe layout and additional controls such as the pressure vessel and water make up container to provide a pressurised central heating system.
(d)
ducting arrangements and selection of duct fittings to produce warm air central heating. Duct system to be extended plenum type and radial or stub duct types.
LO4 IA
3 graphics exercises on the control systems for central heating of which:
(a)
1 question is on wet central heating system controls;
(b)
1 question is on warm air central heating system controls;
(c)
1 question is on the application and use of functional flow diagrams.
PC For (a) and (b) from a list of controls the student should accurately place these in operational sequence and in a schematic diagram:
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Continuation of Module No. 75043
Session 1987-88
(a)
clock, room thermostat cylinder thermostat, boiler thermostat, motorised valve, pump, gas valve.
(b)
clock, room thermostat, limit thermostat, fan control switch gas valve, fan.
(c)
accurately convert a schematic diagram into a functional flow diagram and indicate how these could be used to identify a fault condition.
LO5 IA
Project involving graphics and calculations. Using a given set of plans and reference material for a small domestic building, the student is required to design a wet or dry central heating system.
PC Will be based on: (i)
accuracy of calculations of e.g. for a wet system: heat requirements and boiler power rating and dimensions of all radiators, pipe sizes and water flow rates and pump rating;
(ii)
correctness of the application of the figures to produce a correct layout of the system.
A completed sketch should indicate: (i)
position and power rating of the boiler;
(ii)
position and dimensions of all radiators or registers;
(iii)
pipe or duct dimensions and routes;
(iv)
pump location where appropriate;
(v)
ventilation and construction requirements of the appliance compartment.
02/12/98 Copyright SQA 1987
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