Use Hot Water Pressurized Tanks for Proper Hot Water Pressure
Tal Potishman asked:
Since their successful introduction to the UK market back in the 80s, pressurized water heating systems, alternatively known as unvented cylinders, have proven to be very popular. They are winning hearts both with the general public and the plumbing and heating industry. As an additional confirmation of their success, in 2007 unvented systems accounted for the first time for 50% of the hot water systems installed in the UK.
Unvented systems make a far better solution for water pressure compared with traditional hot water systems. In traditional domestic systems, the water feeder tank, normally positioned in the loft is responsible for filling the hot water tank and building up the pressure in the system. However, the feeder tank is rarely high enough to build enough of a head to create substantial pressure. This leads, for example, to an annoying drizzle from one’s shower rather than a powerful shower.
Unvented systems are sealed and thus have an internal pressure which is likely to increase as the water within the tank heats up. In traditional systems, expansion of water as it heats up is handled by the feeder tank, which easily accepts any such expansion. For unvented systems, the solutions come in the form of specially designed checks and safety equipment to ensure safe and reliable operations even as water heats up and expands.
The sealed nature of the system led to some technological developments that were needed to address issues such as water expansion. As water heats up it expands and increase the volume it occupies. Traditionally this was easily addressed by the feeder tank absorbing any such expansion of the water. For unvented systems, however, a set of safety solutions has been designed to ensure safety is maintained at the highest level while still allowing for reliable and efficient operation.
Legally certified unvented cylinders must meet the UK standard for safety measures to ensure that pressure build up within the sealed system does not pose a problem. The systems therefore rely on a combination of technical solutions. An expansion vessel is normally attached (externally or sometimes internally within the cylinder) to absorb expansion in the volume of the water due the heating. These vessels can handle up to around ten bars of pressure, addressing major expansion in the system.
Another safety measure is the temperature and pressure relief valve. The PT valve is a simple yet smart mechanical valve which senses whether the temperature or the pressure within the cylinder is too high (or is breaching a preset level). At that point the valve opens up to let the extra steam out into the drain, thus immediately reducing the temperature, the pressure and the volume of water in the system.
The above safety checks and measures ensure safe operations and full protection for the users. By replenishing hot water drawn by the user with fresh cold water, the system sustains a steady pressure (which is equal to the mains pressure). Hot water is normally drawn from the top of the cylinder (which is where the rising hot water accumulates due to gravity) and the cold water is normally entered via the inlet at the bottom of the cylinder rising up as it warms up.
Unvented cylinders are typically grouped into one of the following two groups - direct and indirect:
* Direct cylinders - normally use an electrical heating unit to heat the water. The electrical unit (often referred to as an immersion heater) is immersed within the water inside the cylinder and has a typical heating capacity of 2.5 to 3.6 kW to heat up the water electrically.
* In-direct cylinders - using a heat exchanger, the water in the cylinder acquires the heat from the heating medium. Typically a boiler is used to heat up water which is then pumped through the heat exchanger where it loses its heat to the water inside the cylinder. This system is widely used in conjunction with solar thermal systems.
Unvented systems have proven to be an improvement on the old hot water systems, offering higher pressure and better performance. With competition helping to improve availability and reduce prices, unvented systems are likely to grow in popularity.
Philip
Since their successful introduction to the UK market back in the 80s, pressurized water heating systems, alternatively known as unvented cylinders, have proven to be very popular. They are winning hearts both with the general public and the plumbing and heating industry. As an additional confirmation of their success, in 2007 unvented systems accounted for the first time for 50% of the hot water systems installed in the UK.
Unvented systems make a far better solution for water pressure compared with traditional hot water systems. In traditional domestic systems, the water feeder tank, normally positioned in the loft is responsible for filling the hot water tank and building up the pressure in the system. However, the feeder tank is rarely high enough to build enough of a head to create substantial pressure. This leads, for example, to an annoying drizzle from one’s shower rather than a powerful shower.
Unvented systems are sealed and thus have an internal pressure which is likely to increase as the water within the tank heats up. In traditional systems, expansion of water as it heats up is handled by the feeder tank, which easily accepts any such expansion. For unvented systems, the solutions come in the form of specially designed checks and safety equipment to ensure safe and reliable operations even as water heats up and expands.
The sealed nature of the system led to some technological developments that were needed to address issues such as water expansion. As water heats up it expands and increase the volume it occupies. Traditionally this was easily addressed by the feeder tank absorbing any such expansion of the water. For unvented systems, however, a set of safety solutions has been designed to ensure safety is maintained at the highest level while still allowing for reliable and efficient operation.
Legally certified unvented cylinders must meet the UK standard for safety measures to ensure that pressure build up within the sealed system does not pose a problem. The systems therefore rely on a combination of technical solutions. An expansion vessel is normally attached (externally or sometimes internally within the cylinder) to absorb expansion in the volume of the water due the heating. These vessels can handle up to around ten bars of pressure, addressing major expansion in the system.
Another safety measure is the temperature and pressure relief valve. The PT valve is a simple yet smart mechanical valve which senses whether the temperature or the pressure within the cylinder is too high (or is breaching a preset level). At that point the valve opens up to let the extra steam out into the drain, thus immediately reducing the temperature, the pressure and the volume of water in the system.
The above safety checks and measures ensure safe operations and full protection for the users. By replenishing hot water drawn by the user with fresh cold water, the system sustains a steady pressure (which is equal to the mains pressure). Hot water is normally drawn from the top of the cylinder (which is where the rising hot water accumulates due to gravity) and the cold water is normally entered via the inlet at the bottom of the cylinder rising up as it warms up.
Unvented cylinders are typically grouped into one of the following two groups - direct and indirect:
* Direct cylinders - normally use an electrical heating unit to heat the water. The electrical unit (often referred to as an immersion heater) is immersed within the water inside the cylinder and has a typical heating capacity of 2.5 to 3.6 kW to heat up the water electrically.
* In-direct cylinders - using a heat exchanger, the water in the cylinder acquires the heat from the heating medium. Typically a boiler is used to heat up water which is then pumped through the heat exchanger where it loses its heat to the water inside the cylinder. This system is widely used in conjunction with solar thermal systems.
Unvented systems have proven to be an improvement on the old hot water systems, offering higher pressure and better performance. With competition helping to improve availability and reduce prices, unvented systems are likely to grow in popularity.
Philip
