Domestic hot water installations
Domestic hot water (DHW) system is required in buildings for showering, bathing, clothes and dish washing, etc. It makes use of two resources, water and energy, and therefore retrofitting efforts should respect proper DHW system installation.
Average hot water demand in educational building operated 250 days a year runs at 5-15 litres a day and person in schools without showers and 30-50 litres in schools with showers at 45°C. Average lifetime of DHW equipment is 10-15 years. Most of DHW systems in EU make use of gas and oil as an energy source, 30% are powered by electricity.
Proper systems should meet the following requirements:
- continuous and instantly water flow at desired volume and given temperature
- low capital and operation costs
- easy regulation of temperature
- easy to maintenance and reliable in use
- proper water quality, legionella disaster proof

DHW systems development and retrofitting activities according to European Union Directorate General for Energy and Transport:
- inefficient instantaneous electric heaters replacement with systems that will aid peak power management (e.g. energy efficient storage-type DHW systems, instantaneous gas heaters, solar-assisted systems)
- equipment improvement, e.g. highly efficient instantaneous gas heaters, gas, oil and electric storage heaters, and efficient distribution systems and components
- developing of appliances that minimise hot water use, e.g. low flow rate, high pressure showerheads, faucet and showerhead aerators, hot/cold water mixers, optimised volume bathtubs, improved washing machines and dishwashers
- developing kits to facilitate the retrofitting of solar systems onto existing storage-type DHW systems
- developing integrated heat recovery/water heating systems that use warm "grey water" for pre-heating feed water in centralised DHW systems in the residential and non-domestic sectors
- researching and demonstrating units that combine compressive refrigeration with storage-type DHW systems.

A classification and description of existing Domestic Hot Water Systems (DHWS) available and some suggestion for selecting DHWS systems are given, including a list of advantages and drawbacks.