Pressure and Thermal Store Hot Water Tanks

Introduction to hot water tank options

Every country in the world (almost) has a manufacture of hot water tanks produced from a varied number of materials, copper, to glass lined steel to plastic. The very big mass producers in the world require volume orders in order to invest in automation of a standard range of tanks and nothing much else. The small manufactures offer bespoke designs to suite the clients’ personal needs and that the tank will fit into the space available in an existing home or business cupboard/cellar.

This section is not about tank sizes, mass production or bespoke, material used or if installed on the roof or inside the house. I designed the first thermal store concept in 1997, which explained in simple terms is a buffer tank of water, open vented, made from any type of material, none pressure, but able to provide hot water at mains pressure. Below are some of my own proven reasons I can give from experience and living with such a tank design system where a 100% renewable energy resource like solar thermal and less of a renewable resource that of hot water generated by a air to water heat pump is consider to provide both hot water at mains pressure and space heating all from a single tank.

Every government in the world is aware of the affects of global warming, but not how to reverse it at no cost. Right now solar photo voltaic (PV) is seen as resolving part of the problem, but at a huge cost to somebody in the Feed in Tariffs that are paid out to those who can afford such a system by those who cannot
Heating a tank of water by solar PV, is both wasteful of resources and without government support would die a death in countries where there are no power cuts as yet.
In a growing number of hot countries, winters are getting colder to the point of freezing at night times, which is increasing the need for heating, not just hot water.

  • The majority of hot water tanks mass produced are of the pressure type, made of mild steel, with a glass lining to prevent rusting.
  • Also gaining sales is stainless steel as a lighter material, but higher cost.
  • The choice of heating these tanks is through an electric heating element or a heat exchanger coil inside connected to a gas/oil or electric boiler.
  • Both types of tanks provide one only use, the supply of hot water at mains pressure from the city supply into the house and into the bottom of the tank, with hot water out the top.
  • These tanks have to include safety protection to avoid bursting open if the pressure from a to higher temperature allows that to happen.
  • Using the UK as an example, there are 3 safety valves to make sure a tank of hot water does not burst open.
  • The growing solar water heating market which gains less publicity and support as solar PV does, has seen a 2nd heat exchanger coil added to the first one, which has moved up the tank as the secondary heating source.
  • Adding a high performing solar heat pipe collector to a unvented pressure tank, where the energy source (the Sun) cannot be controlled unless the programmer shuts off the circulating pumps, adds further to such a tank over heating and reducing its working life.

The alternative is a Thermal Store (A buffer tank, is a tank of water that when filled is not for drinking use thereafter or showers etc). The mass producers of pressure unvented tanks, sold as a hot water tank only product, have no interest in mass producing thermal stores for many reasons I wont go into in this introduction. The picture on the left shows one of two options to gain hot water at mains pressure through a none pressure tank as well as hot water for space heating from the water inside the tank, none potable.


So what is the Alternative and why do we need to consider it?

Decide for yourself from the points below:

  • Less metal material used and light weight.
  • Open vented (none pressure) requires no safety valves, as a water top up and vent tank of 10 litres placed above the thermal store is all the difference is costing less that $50.00
  • A true Thermal Store has no heat exchanger coils inside to scale up or leak, as the exchange of cold water into hot water is carried out in a box outside the tank itself ( as shown in the picture above.
  • A Thermal store in affect is a multi fuel heating system, as it allows any number of heat producing appliances to be connected to this type of buffer tank.
  • Number one is always an array of solar thermal collectors to make day time support heating viable, followed by a air to water heat pump if only electricity is available, with other options of a wood burning stove and finally a gas/oil boiler if heat demand is large.
  • An opened vented thermal store also means less worry about over heating to above 65-70c as is the cut off for unvented pressure tanks.
  • To limit the temperature to below 90c in summer months when there is no space heating requirement, there are many proven ways to use this excess hot water in the summer months.
  • No servicing of a thermal store is required as no danger in valve failures reducing running costs to the consumer.
  • The life of a thermal store is much longer as there is no stress on any of he tank joints from expanding water pressure.

Ask yourself this question if you see solar thermal free hot water as a viable resource we should all look to use for both hot water and space heating, WHY BUY A HOT WATER TANK THAT CAN ONLY SUPPLY A TANK OF WATER HEATED BY SOLAR AND A BACK UP THAT HAS TO BE SHUT DOWN AT 65C ON A DAY IN THE WINTER, WHEN THAT WATER COULD BE PASSED INTO YOUR HOME/BUSINESS HEATING SYSTEM?

Feel free to contact me with any questions to this tank issue, when considering investing in solar thermal hot water and space heating.