Module 2 Hot Water System Flashcards
Localised hot water heaters explain?
Also known as point of use , heat water for single appliances, showers, under sink, they can come in 10litres or 30-40 litre
Centralised hot water supply explain??
They usually take the form of hot water cylinder or calorifier which stores hot water for later use
What else can be used to centrally or instantaneously heat water?
A combination or multi point boiler
What are the 2 different systems hot water is stored?
Direct or indirect, they can also horizontal and vertical
Direct cylinder system of hot water supply talk about it??
When central heating is NOT installed bin a house the direct system may be used
In the direct cylinder system what does it supply?
All the hot water drawn off the taps has passed through the boiler
What are the main equipment required for the direct system of hot water supply??
1) cold water storage 2) direct cylinder (no coil) 3) direct back boiler
What is other names for the secondary flow?
Hot water supply/ service/ distribution pipe/ vent pipe
Explain how hot water can be heated or stored??
Hot water is usually heated in what is categoried local or centralised, in addition to this hot water can be heated INSTANTANEOUSLY or more commonly preheated and stored
In the event of the water in the cylinder heating to 100’ where does the water go?
The extra water is pushed out of the vent pipe this is not considered normal expansion as it is steam
What is the cold feed also know as and why?
Cold feed and expansion pipe because under normal heating in the cylinder the expansion of heat will go back up the cold feed as its the easier route
Explain the term gravity circulation?
When the boiler is heated the water becomes lighter as it expands and is then transferred by convection current up to the cylinder via the primary flow pipe this form of hot water heating brought about by convection current is known as GRAVITY CIRCULATION
What is the direct supply of hot water??
This method of hot water supply all of the hot water drawn off at the taps has passed through the boiler
In designing the direct cylinder system where is best place to put cylinder and why??
It’s as close to the boiler as this will prevent excessive heat loss from the circulation pipes, the higher the cylinder over the boiler the faster the flow between the two
Why should steel valves or fittings never be used on direct system??
The steel will rust
How is the boiler for direct system heated and how long does it take?
They usually heating up period is between 1/2 hour and 1 1/2 hours, there are several methods of heating the water most traditional being a range with internal boiler in the kitchen or back boiler behind an open fire
The direct back boiler are made from what material and why?
Generally made in stainless steel or copper, as this system has a continuous supply of fresh water passing through it so these materials must be used to prevent corrosion and discolouration of the water
What is important about the angle when installing primary flow and return pipes??
They should rise steadily from the boiler to the cylinder to prevent air locks and also improve circulation
What is important when installing the hot water supply pipe??
This should be connected to the top of the cylinder and prevent (one pipe) circulation it should run almost horizontal for at least 457mm out from the boiler before the vent pipe goes up
What is the minimum size vent pipe to be used and why?
In domestic plumbing systems the min diameter is 22mm as smaller pipes would be prone to obstruction
What is the main function of the vent pipe??
1) maintain atmospheric conditions in the pipe work to prevent a vacuum building up 2) permit the escape of air 3) in event of water boiling it allows it to discharge over the feed cistern
How does air form and also escape out of the cylinder?
Air bubbles will form when fresh water is heated and or its pressure is reduced, the vent pipe will release this air from the cylinder
How is the height of the vent pipe determined??
It should be 1/16 the height from the bottom of the cylinder to the water level in the cistern
Know
Care should be taken not to take a draw off too high on the vent pipe as this could draw in air or lead to a NO FLOW situation
What flanges can be used on the top of cylinder for a pumped supply ??
A Surrey or warrick flange it pulls water from the hot zone without effecting the vent pipe
Where should you never draw an appliance from?
The cold feed pipe
What can be reasons for drawing air into a pipe?
Insufficient diameter of the cold feed pipe as the smaller cold feed would not be able to supply a peak demand on the hot water supply pipe water and then air would be drawn down the vent pipe to compensate also If The cold feed was teed off the an appliance
What is one pipe circulation?
It’s a form of circulation in which bathe circulatory flow band return of hot water takes place in the same pipe,
How can you prevent one pipe circulation?
Run a vent pipe 457-460mm away from the cylinder
What is dead legs ?
it’s a term used to describe a situation where old water has to be drawn off from a hot tap before a supply of hot water is obtained
How is dead legs caused??
By the hot water storage vessel being fitted a long way away.
How would you prevent a dead leg?
Keep the hot water vessel close and centralised
To avoid wasting energy and hot water a distribution system should be designed so that hot water appears quickly at draw off taps when opened
Commercially secondary return circuits are frequently required due to unavoidable long pipe runs
How is a secondary circulation achieved?
By fitting a secondary return pipe after the last hot water connection Bon the system
Where should the secondary return be on the cylinder?
It should connect to the top 1/3 of the cylinder if lower it can mix with colder water and reduces its overall temperature
What can be fitted to a system when a gravity circulation secondary return can’t be formed?
A non corroding circulation pump (bronze pump) and should be fitted colour to the cylinder
It’s normal to fit a time switch controlling the pimp as it can switch off when there is no hot water demand
Know
What can be used as an alternative to a secondary circuit?
Tracy heating can be used to keep the pipe temperature up
When is the indirect system of hot water supply used?
When central heating IS installed in a house it is not usual to use the direct system of hot water supply
Give reasons for not using the direct system?
Radiators would rust from the oxygen content as they are made from steel, this could cause discolouration of the water at the hot water tap,
What are the main equipment needed for an indirect system?
A boiler (steel or any metal) an indirect cylinder (cool fitted) a feed and expansion cistern
What else can the indirect system be know as?
The open vented, indirect, hot water heating, system
What size cistern souls the system have?
A 45 litre feed and expansion cistern located in the roof space to supply the system
Know
A 13mm (1/2”)connection is taken from the cistern and connects to the return pipe close to the boiler,
What are the sizes of the pipes used on the indirect system?
25mm primary flow , 22mm minimum open vent, 25mm primary return pipe,
What are cool heat exchangers??
They are water to water heat exchanging devices named cool as they are usually a series of circular winding made from conductive pipe work such as copper
What are the difference types a cylinder coils can come in?
They have a single twin (dual) or triple coils to input or extract heat
What are coils made from and how?
They can be made from multiple layers of smaller pipe large diameter pipe or finned copper pipe
What is duplex stainless steel cylinder?
It is a rapid reheat (17min) offers superior corrosion resistance to copper glass lined
What are high recovery coils?
They should always be used as they are quicker to heat they are more economical
When fitting an indirect system of hot water supply what 4 points must be observed??
A) position of the cylinder b) the boiler c) position of the cold water storage cistern d) the feed expansion cistern
When filling the expansion cistern where should the water level be??
It should be set sufficiently low so that when the water heats up and expands it will not rise to a point higher in the cistern than 25mm below the overflow or warning pipe
Where is the ball valve in the expansion Cistern?
That and the overflow are in the same positions as in the storage cistern how ever the ballvavle Are is adjusted to a significantly lower level
What is the guideline temp for water to be stored at?
Not less than 60”c
What is stratification??
This is the term given to the formation of layers of water in the hot water storage vessel from the hottest at the top Dow through the temperature range to the coolest at the bottom
To enable stratification to work to its maximum efficiency what must be encouraged to be done??
Have a cylindrical shape vessel the taller the better fitted in a vertical position
Where should the cold feed be in the cylinder to maximise heat?
It should be at the bottom so that incoming cold water does not disturb or destroy the existing stratification
Cylinders can be heated by electricity explain how?
By a 3KW electric immersion heater they can be single or dual immersion elements to cater for filling a sink or a bath full of hot water, they can be top entry or side entry using a shorter length
What are safety overheat stats?
They are necessary on all electric immersion heaters to avoid the potential of scalding
Where is the Willis heater fitted and used?
Can be used to fit a short immersion where a side or top entry boss is not available,
What is a boiler??
A boiler is simply an enclosed vessel in which water is heated by application of heat which could be either from solid fuel pellet gas oil or electricity
What are the different types of boiler?
Combi boiler kitchen/utility boiler system boiler solid fuelled back boiler bra fe or stoves
What are oil burners??
These boilers are heated by pressure jet oil burners can be diesel or kerosene
What are the two types of back boilers ?
Cast iron or steel boilers
What are solid fuel boilers?
They burn wood coal turf or anthracite, they are only suitable for the open vented central heating system
What are system boilers?
They are basically combi boilers with the internal domestic hot water circuit taken away it just heats radiators and the cylinder
What does comi boilers heat?
Hot water taps and radiators
What is a mixing/blending/tempering valves?
They are thermostatic mixing valves and used to control the temperature of water to a tap or shower they are ideal for baths or sinks
How hot is too hot to children??
60” in 1 sec. 55” in 10 sec 50” in 5 minutes
Why do we store water at 65”c?
To kill bacteria (legionella) to have more quantity of warm water available when mixed and to allow for cleaning greasy pans kitchens etc
What temp should water be at. Ablutions such as toilet sinks??
45”c where children are present this is very important in schools childcare facilities and elderly care institutions
Remember
Shower mixers should be thermostatic, the cold feed to the cylinder should always be higher than the cold distribution feed in the cistern
What are the max recommend hot water outlet temp?
Bidet 38”c shower 41”c washbasin 41”c bath 44”c supervised 46”c
What are air locks ?
They are a very common cause of trouble with both hot water and heating system cause by unventilated arches formed in badly befitted pipe work
What are causes of air locks?
Sagging pipes, unventilated arches, not laid horizontal or with appropriate falls,
What temp does scale deposit start at??
Happens at 55”c and above in hard water
Why does a cylinder collapse?
Due to the pressure on the inside of the cylinder becoming less than that of the atmosphere
