Central Heating Systems

Flashcards about domestic central heating system installation and maintenance techniques

What is the purpose of central heating systems used in dwellings?

To provide a set of conditions within a building that make us feel thermally comfortable.

What is humidity?

The amount of moisture in the atmosphere within an environment, given as a percentage.

What is the ideal humidity range for humans?

Between 40-60%.

Why are air changes required?

To remove a CO2 rich atmosphere and replace it with Oxygen rich air.

How many air changes per hour are required for a lounge, bathroom/kitchen, and bedroom?

Lounge: 2, Bathroom/Kitchen: 3, Bedroom: 1.

What are the optimum temperatures for human comfort?

22oC in the winter and 23oC in the summer.

What does air velocity refer to?

The speed at which air travels through the building.

What is the optimum air velocity?

0.2 to 0.25 m/s.

How does clothing affect thermal comfort?

The more clothing worn, the less air temperature is needed.

Which demographic often feels the cold more intensely?

Older and infirm people.

When is thermal comfort achieved?

When a balance between the body and its surroundings has been achieved.

Define full central heating.

The simultaneous heating of all spaces in a dwelling to maintain specified temperatures based upon calculated heat losses.

Define background heating.

The simultaneous heating of all or some of the spaces in a dwelling to temperatures below those specified based upon calculated heat losses.

Define selective heating.

The simultaneous heating of some of the spaces in a dwelling to maintain specified temperatures based upon calculated heat losses.

What is a one pipe system?

A system that uses a single circuit of pipework runs from the boiler and back, connecting each radiator in turn.

What is a two pipe system?

Two circuits of pipework - a flow circuit and a return circuit - to distribute the heated water to the heat emitters.

Define low pressure heating.

A heating system that operates at temperatures below 100oC because it includes an open vent pipe.

What is the purpose of the open vent?

Prevents heating systems from exceeding 100oC and assists with accommodating the expansion of water due to the water being heated.

Define sealed heating.

A heating system that does not contain a vent pipe or feed and expansion system.

What is gravity heating?

A method of heating water that uses conduction. When water is heated, it expands and loses density, the lighter, hotter water then flows upwards to the heat exchanger.

What is a microbore system?

A system of heating that uses very small pipework to the radiators, typically 8mm and 10mm pipework.

What is a manifold?

A fitting or component that allows multiple pipe connections in one place.

What is a Feed and Expansion Cistern?

A small, usually 10 litre capacity, cold water cistern that is connected to a low-pressure heating system for system filling and to allow water to expand in to it when heated.

What is a filling loop?

A temporary connection between the mains cold water supply and the heating system for filling and pressurization.

What can be used to heat water in wet central heating systems?

Gas, oil, or solid fuelled appliances or by environmentally friendly sources.

In a one pipe low pressure system what is usually connected via swept tees?

Radiators.

In a one pipe system, each successive radiator is fed with water that is around how much cooler than the previous radiator?

Around 4oC.

What is the purpose of the heat leak radiator?

To disperse any excess heat to the surrounding atmosphere.

What type of temperature control do solid fuel appliances use?

Mechanical temperature control.

With a Honeywell C Plan system, what is the purpose of the two-port motorized zone valve on the primary flow into the cylinder?

This is linked to a cylinder thermostat placed on the hot water storage cylinder to control the secondary hot water temperature.

How did heating systems become fully pumped?

By the inclusion of a motorized valve or a series of motorized valves.

In a Honeywell Y Plan, if both heating and hot water are needed, what position does the valve enter?

The valve enters a mid-position allowing water to flow around both the heating and hot water circuits

What is the Honeywell W Plan designed to do?

Designed to give priority to the hot water circuit

What is a sealed heating system?

Is a system that does not contain an open vent pipe and is, in effect, sealed off from the atmosphere.

What are the benefits of heating water that is around 1 bar pressure?

Air infiltration through the open vent pipe is eliminated. Higher water pressure means better flow rate through the system. Higher temperatures can be used if required.

What is the Building Regulations Approved Document L1?

States all dwellings must be zoned between the living space and the sleeping space in a dwelling to give individual time and temperature control across these zones.

How does the S Plan sealed system layout compare to its low-pressure version?

The S Plan sealed system layout is almost the same as its low-pressure version.

By how much does water expand when heated?

Water, when heated, expands by 4%.

What is one of the biggest problems in central heating systems?

Trapped air.

What is the minimum head of pressure required between the F&E cistern and the central heating circulating pump?

1.5m.

What is the correct order for the open vent, cold feed, and pump connections?

Vent, Cold feed, Pump.

How does air is released from open vented heating systems?

Air is released from open vented heating systems as the system fills.

What does the expansion vessel contain?

Contains a neoprene rubber diaphragm. One side is full of air and the other contains the heating system water.

Why are microbore systems connected to two flow/return manifolds?

Microbore systems should be connected to one flow/return manifold pair to supply the living space and another to supply the sleeping space.

What are the most common solid fuel appliances?

The most common solid fuel appliances are high output back boilers, room heaters, cookers, and independent boilers.

What grade of oil oil do most oil fired appliances for domestic heating systems use?

28 second viscosity oil.

When natural gas is combusted, what do the resulting flue gases contain?

Water vapour.

What are the energy efficient systems are suitable for use with traditional, system, and combination boilers?

Solar hot water supply and underfloor heating systems.

For a forced draught room sealed appliance what is a postive pressure?

Positive pressure – where the fan is positioned before the gas burner. The fan forces gas and air to a pre-mix gas burner where it is combusted. This creates a positive pressure inside the boiler casing. Generally used on condensing-type boilers.

How do natural draught open flues function?

Natural draught flues rely on the up-draught of the flue, which is created because the heat from the combustion process rises.