5 Hot Water Systems: Installation & Efficiency

• Installation requirements for domestic hot water plumbing systems covered
• Installation requirements for domestic hot water systems include:
  • Keeping efficiency
  • Dead legs
  • Secondary circulation
  • Trace heating
  • Pipe Protection
  • Fluid Categories
  • Water Regulations
  • Backflow, Back Pressure and Back siphonage
  • Contamination

Keeping Efficiency

• Once water is heated, the system needs to retain heat and supply hot water effectively on demand
• Heat loss is minimized by insulation on the cylinder and pipework per Building Regulations part L
• Control is needed on the length of pipe used to deliver hot water to the outlet
• Waste of cold water occurs before hot water is drawn off
• Hot water left in the pipe cools down, which reduces the efficiency

BS EN 806

• BS EN 806 establishes maximum pipe length before it becomes a dead leg
• 12 - 22mm – 12m is the maximum length
• 22 - 28mm – 8m is the maximum length
• over 28mm – 3m is the maximum length
• Water Regulations recommend the temperature at a terminal fitting must not be less than 50°C within 30 seconds after fully opening

Active Dead Leg

• Active dead leg refers to the need to draw off a lot of cold water before hot water reaches the outlet
  • This causes a waste of water
  • Also a waste of heated water left in pipe

Passive Dead Leg

• Passive dead leg refers to a section of pipe that has been capped off, where water cannot flow or be drained off
• Stagnant water can build up in a passive dead leg
• Legionella and bacterial growth can occur in passive dead legs
• Passive dead legs must be kept to a minimum length after appliances have been removed

Overcoming Dead Legs

• To overcome a dead leg, localised hot water can be installed, or the use of a secondary circulation should be used
• Dead legs can be overcome by:
  • Bronze pump
  • Return
  • Smaller return pipe
  • Essex flange
  • Top one-third of cylinder
  • Timer control

Secondary Circulation

• Secondary circulation brings the circuit of hot water much closer to the outlet point
• Systems are fitted with long pipe runs (dead legs) with secondary circulation
• The connection to the cylinder for the secondary circulation should be made in the top third of the cylinder, commonly using an Essex flange
• The return pipe to the cylinder can be a smaller diameter than the flow
• Systems are often on time clocks to save energy when hot water is not demanded

Trace Heating Element

• In vulnerable situations where there may not be any heating underneath the insulation on a hot water pipe, a trace heating element can be used
• A low temperature heating element attaches to the outside of the pipe, controlled by a thermostat to prevent freezing
• It can also be used to overcome waste of water in active dead legs

Location of Pipework

• Consideration needs to be taken where and how to install pipework to avoid issues such as:
  • Unsightly appearance
  • Creaking in joists due to expansion and contraction
  • Transfer of heat if the hot pipe is below the cold pipe
  • Insulation in vulnerable areas
  • Refer to BS EN 806
  • The Water Regulations

Cold Water Heating Up

• Cold water can warm up when hot and cold water pipes are too close together, transferring heat
• Hot water pipes should be installed above cold water pipes
• Hot water pipes should be insulated to avoid heat transfer and heat loss
• If the hot water cylinder overheats, the vent pipe discharges into the CWSC, which can also warm the cold water up
• BS8000 pt15 says the hot pipe should be above the cold pipework and that the pipe should be insulated if there is any possibility of heat transfer

Pipe Protection

• Pipe protection is needed for multiple reasons:
  • Damage
  • Frost/Freezing
  • Heat loss
  • Being drilled into (pipe guard)
  • Plastic pipe locations (metal tape)
• Hot water pipes in vulnerable places should be protected by insulating the pipes
• Vulnerable places include:
  • In a suspended ground floor void
  • Unheated garage or room
  • In the loft area

Fluid Categories

• Fluid categories range from 1 to 5, each representing a different level of health risk and requiring specific protection measures:
  • Category 1: Wholesome water from the water undertaker. Example: Mains water. Protection: None
  • Category 2: Water that would be Cat 1 except for colour, odour, appearance/temperature. Example: Hot water in cylinder, softened water. Protection: Single check valve
  • Category 3: Fluids representing a slight health risk, not suitable to be drunk. Example: Primary water, bath/shower water, washing machines/dishwashers. Protection: Double check valve
  • Category 4: Fluids representing a significant health risk, containing toxic substances. Example: Commercial primary water, microorganisms, pesticides, swimming pools. Protection: RPZ valve
  • Category 5: Fluids representing a severe/serious health risk, containing pathogenic organisms, radioactive, faecal matter. Example: Urinal, WC, bidets, grey water, medical rooms, laboratories. Protection: Air gap

Water Regulation Responsibility

• Under the Water Regulations, responsibility exists to prevent contamination of wholesome water within a property:
  • Non-approved material should not be used
  • Stop backflow
  • Stop back pressure
  • Stop back siphonage
  • Avoid cross connections
• Prevention is achieved by either an air gap or mechanical means

Backflow and Back Pressure

• Backflow occurs when water flows in the wrong direction due to loss of system pressure
• If mains cold water shuts off for repairs, cold water in the plumbing system would backflow into the water main, this is called Back pressure

Contamination and Back Siphonage

• Back siphonage occurs when the pressure at the water main supply end drops suddenly
• Back siphonage creates a vacuum, sucking water backward