Temperature, Pressure & Hot Water Systems

Hot Water

• People need hot water to keep their bodies and living areas clean.
• A regular supply of hot water is required to break down and dissolve oils and dirt.
• Some substances, like fatty foods, need at least 60°C to dissolve.

The Law

• The Building Act 2004 governs the building industry in New Zealand.
• The Act seeks to improve control and encourage better practices in building design and construction.
• The objectives of the New Zealand Building Code align with the Building Act's purposes.
• The Code defines required building performance and comprises multiple clauses, including clause G12.

Means of Compliance

• The Building Code includes clauses like G12, containing compliance documents for hot water supply.
• G12 AS1 is an acceptable solution for hot water supply installations.
• G12 AS1 also links to AS/NZS 3500 Part 4 as a verification method for Building Code requirements.
• All work on hot water services must conform to the Building Code.
• Clause G12 AS1 performance criteria summary for hot water services:
  • Delivered at a temperature that avoids scalding risks.
  • Have adequate flow rates to sanitary fixtures and appliances.
  • Avoid the likelihood of leakage.
  • Allow reasonable access to components needing maintenance, including isolation.
  • Be controllable to prevent Legionella bacteria growth.
  • Vessels used for storing/producing hot water must have safety devices; these devices relieve excessive pressure and limit temperatures to avoid flash steam.
• The textbook covers best trade practices and acceptable solutions of the NZBC.
• It doesn't cover alternative designs at a certifying level.

Building Code Requirements

• Building consent for water heating installation requires compliance with Building Code sections, including:
  • B1: Structure
  • B2: Durability
  • E2: External Moisture
  • G12: Water Supplies
  • H1: Energy Efficiency
• Clause B1 ensures the building's support structure can handle water heating system loads for its lifespan.
• Clause B2 sets durability requirements for installed products like water heating components (generally lasting 15+ years).
• Some components needing maintenance may last less than 15 years if identified in the owner's manual.
• Installers should provide durability information in a Building Consent application.
• Clause E2 protects the structure's weatherproofing envelope from external moisture leakage.
• This clause addresses penetrations of the roof cladding and suitable waterproofing methods.
• Clause G12 protects potable cold and hot water purity and ensures safety.
• G12 includes the acceptable solution G12/AS1, which merges elements of the Building Code.
• If compliance is shown with G12/AS1, it must be used entirely and kept within its scope.
• Clause H1 covers all building structure aspects for energy efficiency. This outlines storage vessel and pipe insulation needs for water heating systems.
• Clause H1 references NZS 4305 for domestic electrical and gas systems up to 700 litre storage.
• The NZBC does not control larger systems and piping.
• Clause H1 includes ways to conserve water and energy by minimizing pipe runs.

Hot Water Science

• When heated, water undergoes various changes:
  • Volume changes, though practically incompressible.
  • Boiling point changes.
  • Dissolves and expels gases.
  • Some solids dissolve within it.
  • May become corrosive.
  • Flows differently.
• Standard piping or cylinders cannot restrain forced water in a container.
• Water expands when it freezes and when it is heated.
• Water's expansion during freezing can damage pipes.
• Heated water becomes less dense and rises and forms layers, known as stratification (hottest water is at the top, coolest at the base).
• Water density peaks at 4°C.
• Expansion from 4°C upwards is not constant, but greater at higher temperatures.
• Expansion between 4°C and 100°C is roughly 4% of the original volume.
• For water heated from 10°C (cold) to 65°C (hot), the expansion will be 2-3% of its original volume.
• Water expanding is usually released via an expansion valve, generating pressure proportional to heat input.
• Pascal's Law says pressure applied anywhere to a confined fluid is transmitted with undiminished force across it in every direction.
• Heated water may explode if expansion isn't accommodated.
• Explosion force depends on vessel material strength and construction.
• The Building Code requires people to be safeguarded from hot water-related explosions and flash steam production.
• The relationship between water temperature and pressure in boiling water must be remembered.
• Water heating systems need correct installation to prevent excess temperature and steam production.

Avoiding the Creation of Steam

• Water becomes steam at 100°C at sea level in an open container (electric jug).
• Water boiling under pressure (pressure cooker) has a significantly higher boiling point.
• Water changing from liquid to steam has a violent force.
• During steam conversion, hot water will expand explosively as a gas.
• Steam inside a water storage vessel can be dangerous.
• If steam forms/condenses back, this may create a vacuum and collapse the cylinder.

Types of Water Heaters

• Water heaters can be for single point use or central storage.
• Building design, occupancy, and use will determine appropriate systems.
• Long pipe runs supplying one hot tap ("dead legs") are uneconomical; these waste water/cause heat loss.
• Clause H1 defines flow minimums and maximums for draw-off points.
• Single-point electric or gas heaters can prevent dead legs.
• Possible water heater choices include:
  • Instantaneous water heaters.
  • Storage water heaters (high, medium, or low pressure).
  • Heat exchange (coil) storage water heaters.
  • Boiling water heaters.

Water Capacity

• Water supply system capacity varies. Average water use is 40-60 litres a day; the capacity should be factored with those figures.
• Determining hot water capacity variable factors:
  • Number of people to be served.
  • Number of appliances using hot water, especially showers.
  • Dwelling size.
  • Winter cold water temperatures.
  • User's standard of living.
  • Users Habits
  • Spa baths.
• Water heaters should be sized for the accommodation potential rather than the present users.
• Systems should accommodate peak load/maximum demand.
• Peak demand can be calculated through Building Code flow rate tables, manufacturer's information (e.g. Rinnai: 30–40 l/hr).
• The potential of the home must be considered for water heater sizing, appliances, etc.

Types of Energy Sources

• The type of energy source will decide the choice of water heater.
• Energy sources:
  • Electricity (single phase immersion elements, three phase electrode boilers).
  • Solid fuel (wood, coal, pellets).
  • Gas (LPG, Natural gas).
  • Steam (including geothermal).
  • Oil.
  • Solar (solar gain from collectors, heat pumps).
• Energy source choice depends on current/predicted fuel prices, fuel availability, and efficiency.
• Gas water heaters have improved from ∼80% to 95% efficient recently.
• Energy sources have two types: controlled or uncontrolled.
• Controlled heat sources can be regulated to stop heat input (e.g. electric cylinder thermostat), terminating heat when necessary.
• Uncontrolled heat sources have the potential to continuously heat water up to boiling point. Wet-back or solar sources cannot be turned off.

Water Heater Construction

• The Building Code has specific building code requirements for water heater construction, temperature and pressure.
• Unit standards require some knowledge of regulations, standards and codes for maintenance of water supply systems.
  • AS/NZS 3500.4:2003 Plumbing and drainage Heated water services.
  • Clause G10 Piped Services.
  • Clause G12 Water.
• Water heater construction must comply with standards and regulations (NZBC clause G12 AS1 contains list).
• Standards and regulations examples:
  • Low pressure electric copper storage water heaters: comply with NZS 4602.
  • Applies to the design, materials, construction, thermal insulation, and performance of thermostatically controlled heaters of 6.5 l to 450 l capacity (120 kPa/12m head).
  • Vertically-installed/open-vented copper water heaters: comply with G12 and NZS 4603; if valve vented, NZS 4607.
  • Electric storage water heaters (not covered by NZS 4602): comply with NZS 4606 (e.g. mains pressure storage water heaters).
• Parts 1, 2, and 3 to this standard specify constructional and performance requirements for 6.5-630 l storage water heaters.
• Specs for heat loss allowance.

Materials

• Topics discussed include construction, components, and materials of water heaters.
• Cylinders use various materials, including copper or stainless steel.
• Copper cylinders: suitable for low to medium pressure; medium-pressure cylinders require thicker copper.
• Stainless steel: needs corrosion/stress-cracking resistance for hot water heaters.
• 2304 Duplex: commonly used in water heaters, low-alloy duplex stainless steel, high-strength, and low-cost.
• 2205 Duplex Stainless Steel: is a medium-alloy duplex stainless steel with higher corrosion resistance.
• Water supplies with high chlorine content (50+ ppm): stainless steel cylinders may need a sacrificial anode.
• Systems should use the same/similar materials where possible; combining independent cast iron boilers and half-hard copper cylinders makes this unavoidable.
• Joints in copper cylinders, copper and brass bushes: generally zinc alloy/silver-alloy brazed.

Effect of Pressure on Cylinder Construction

• Cylinders require labeling for operating pressure; damage will occur if the limit is exceeded.
• Some New Zealand manufacturers produced jacketed vitreous enamelled steel cylinders that appeared to be mains pressure units without actually being mains pressure systems. Open vent only labels are the primary indicator of the distinction.
• Low/medium pressure cylinders: labelled with pressure (meters head); example, 7.6m head=cylinder's maximum working pressure and cylinder tested at 120 kPa.
• Mains pressure cylinders are labelled with pressure (kPa).
• Excess pressure on copper hot water cylinders can be dangerous.
• Cylinders use domed ends for extra strength.
• Modern copper cylinders are supported by dense polyurethane insulation.
• Vitreous enamel lined cylinders are concave (top) and convex (bottom) to withstand pressure.

Effect of Temperature on Cylinder Construction

• The building code requires limitations on temperatures of water heaters, including:
  • Prevention of steam production.
  • Protection of users from hot water.
• Hot water cylinders limited by material; for example, vitreous enamelled steel cylinders must avoid connection to the boiler because they cannot handle extremely high temperatures.
• Maximum temperatures occur at night, if night rate' electricity is used.

Components of Water Heaters

• Components apart storage are protected by many safety components and valves.
• Valves, tempering valves must match outlet for hot water.
• Uncontrolled heat sources place demands on storage vessel, valves, and system components. Different manufacturers make various water heaters for different uses.
• Fuel varies component design.
• The billy on a campfire lacks temp. control/heat retention is energy inefficient.
• Gas water heating: gas burner.
• Electric water heating: element. Boilers: various means (oil, pellet burners). Electric water heaters rated lower than gas/solid fuel burners. Older electric heaters: used to fit 1 kW elements.
• New electric heaters: usually 2 kW or 3 kW elements.
• Correct element rating should be chosen to replace a failed element. More powerful elements draw is limited by wiring; domestic: 2 kW element only may be supported. Electric instantaneous water heaters: 27+ kW (3 phase wiring required). 4 m² solar collector: transfers energy at ∼2 kW/hr.
• Gas instantaneous water heater: 55+ kW.
• Pellet burner: 200+kW.

Water Heater Systems

• Elements must work side by side using the same metal materials.
• Tin plated elements specialize working in conjunction with glass-lined water cylinders.
• In glass-lined cylinders, steel, tin, and magnesium are close, and steel or magnesium is a good solution.
• Other elements cause the sacrificial anode to dissolve quickly, decreasing heater life and voiding the warranty.
• Nickel plated elements require the use of a nickel-plated element in copper cylinders.
• The cylinder and plate element are different metals in solution in the absence of a sacrificial anode.
• Other types of plating will force unnecessary corrosion.
• A incoloy element containing high nickel content will sometimes be implemented, and it will work where the conditions are extreme with the water is known to hard.
• Hard water and a low watt density combine as the ultimate solution to where the element always fails early.
• Less watts in any square cm reduces that the limescale can start affecting all performance.
• Gases or electric water heaters with extra help can act in the same manner as quick-recovery to raise store water.
• Other additional parts such as additional element/thermostat can further provide fast heating.
• Electric boiling water unit cuts the power when steam activates the pressure switch to retain heated water for other short uses.

Thermostats for Heaters

• A thermostat provides temperature selection.
• Thermostats de-energize elements when the water’s set point is reached.
• Most maximums are 70c for vitreous, and others range between 10 and 110 for other commercial applications.
• Learn legionella and storage temps for pockets/sleeves is accessible the cylinders.
• A common thermostat for heating water is a rod type.
• Consisting a little invar steel rod then that metal type is inserted brass like a tube which expands with the invar steel, the tube brass is in contact when waters expands and draws a lever causing contact removal.
• The magnet magnetizes to attract and perform clean snaps on the switch to prevent arcing.
• New cylinders secure the thermostat is held in the copper using metal brackets.
• Extra safety will allow water cannot boil without a storage container, in case thermostat fails to perform the shutoff or valve in the supply.
• Early water heaters, for example, one measure one to make safety measure an option of a gas-cutoff or ECO.
• Modern designs incorporate a fusible link control that resets will require complete replacement.
• Manual can prevent or eliminate a heater and cut overheating or voltage.

Heater Safety

• Sacrificial anode helps with steel components and tin parts.
• Vitreous can even dissolve in high temps and ports may have covered; The water may explode by creating hydrogen gas due to no use.
• The top hot cylinders have the highest corrosive materials/scale buildup.
• Coils or heat exchanges with other water exchangers can easily circulate heat with solar.
• Larger complex controls require a bigger fan or compressor.
• Energy can comply using MEPS by increasing the energy and standards.
• Electric has wool.
• Other K value was replaced using purer materials like purer foam (superceded); Current MEPS use is 50mm.
• Non-flam can use fibreglass
• Safetys or the materials (NZBC) can prevent units from multi-apartment water damages by applying and isolating the unit from damage to the unit.
• Safety is important in hot cylinders over safe trays including pipes and diameter/overflow of piping.
• Tray material differs according voltage and safe trays are common with the resting.

Tank Safety

• Older tanks can crack over on any base.
• Waterproof materials were necessary with an unsafe tank or materials. Galvanized on the tank is necessary; over plastic; gas-fired tanks may be unsuitable (roof over union with air to roof/tray or ceiling.
• G 12 ASI minimum requirements for tanks below 150 liters or flooring. Buildings below tanks fail where the supply fails requiring 50 mm of cold reserve.

Structure Considerations

• For structure support
• There is no such similar to clause restraints required to refer as seismic movements.

Water Supply Needs (Minimum)

Water to heaters must ensure low restrictions and matching to available. Otherwise; water will be lower if water pressure is. G12 ASI minimum support specifications must be met.

Sanitary and temperature flows such as g12 require the lowest possible specified restrictions from the tap.

• In short there must also be a proper adequate way is through taps and ware.
• Also must have a pressure outlet for water (medium or high ( kPa /metres); Tanks such as above requires calculations (rose distance to the water is the distance).

Valves

• They are many valve variants (such as a combination which is in meters head) that the codes or state requirements in the layouts or system. Valves range from (max to overpressure in the temp.) and are continuous to use; failures can be (pressure. temp control etc). safety valves are often installed.
• Should have components like that and can overpressure and control systems.

Maintenance Valves

• Should be easy to drain or maintain the valve
• One method is isolate or tilt systems, these standards are stated by most. Back or pressure valves are often required with that standard to prevent heating being turned off.
• Air systems or breaks are necessary with the main low systems.

Valve Materials

• Ratings must be matched depending on the output of any heater.
• The material/sizing from the heater to relief valves requires much safety protection, using manufacturers standards, and proper connection/cleaning/position, including no overrating valves.
• Vents are always necessary or important for pressure that does not have an output.
• Some high volume or heater has no equal systems/parts.
• The flow/hot/tank has many requirements and isolation techniques are applied for the current standards and hot connections should comply.

Explore the relationship between temperature and pressure in boiling water, and the implications for plumbing and hot water systems. Understand the dangerous scenarios that can occur with steam formation and condensation. Learn about safety features and performance criteria for hot water services, as mandated by building codes.