Condensing water heaters have been manufactured since the 1980s, and now represent a fully mature technology used extensively throughout the world. Terry Plaisted of Automatic Heating outlines the benefits of the condensing water heater.
The condensing water heater is a system of technologies, consisting of the water heater itself fuelled by gas or oil, the flue stack, and the condensate collection system. Condensing water heaters operate at around 95 per cent gross efficiency, compared with 80-85 per cent gross efficiency for conventional water heaters.
They achieve higher efficiencies by using newer technology and by condensing the water vapour that is produced during combustion and trapped in the flue gases.
In traditional water heater technologies, the latent heat contained in the water vapour is allowed to escape through the flue.
Condensing water heaters reclaim that latent heat by condensing the water vapour and transferring its heat to the return water via a secondary heat exchanger with a resultant increase in water heating efficiency.
The flue stack temperature is considerably reduced and the return water temperature raised. Hence the term ‘Condensing Water Heater’.
These potential efficiency gains are achieved if the water heater is operating in or near condensing mode, which requires the temperature of the water returning from the building to the water heater to be as low as possible.
Having said that, condensing water heaters will achieve increased efficiencies over non-condensing water heaters even in a situation utilizing the existing building return water temperature, due to the larger surface area of the heat exchanger in a condensing water heater and the reduced flue temperature.
Optimum return water temperatures are achieved when the return water is below the dew point of the water vapour in the flue gas.
The dew point is determined by several variables, including altitude, outdoor air temperature, and the type of fuel the water heater consumes. The critical variable, however, is combustion efficiency: excess oxygen in the combustion process leads to lower efficiency and requires a lower dew point before condensation can begin.
In general, with efficient combustion, return water temperatures (RWT) should be below 54°C, with lower RWT resulting in more condensation and greater efficiency.
Condensing water heaters require Stainless Steel flues to prevent corrosion. The condensate produced is also slightly acidic so a condensate neutraliser is required before piping condensate to the drain. Plastic piping must be used for the condensate drain to prevent corrosion.
Apart from the obvious cost saving advantages of condensing water heaters, they also offer other benefits. They don’t heat up the plant room (low radiation losses), hot water is supplied when needed (low standby losses) and minimal energy is lost via the flue. The comparatively small footprint of the modern equipment supplied today is also an advantage when floor space is at a premium.
Many plant rooms in Australia house relatively old equipment. It’s not uncommon for equipment to be in excess of thirty years old and property managers can sometimes overlook the fact that this inefficient equipment is costing them a lot more money to run than it needs to.
Many businesses, particularly hotels and aquatic centres are still spending tens of thousands of dollars more on heating than they need to every year because of low-efficiency equipment, outdated technology and suboptimal system maintenance.
Interestingly, a client of Automatic Heating compared their gas usage data from before and after a recent installation of three Modulex 770kW condensing water heaters and reported consistent savings of in excess of 20 per cent with monthly gas usage on average reducing by more than 500,000 MJ.
Gas condensing water heaters are an ideal choice when you want a highly efficient heating system. They achieve a high thermal efficiency by using waste heat to pre-heat the return water entering the water heater. Quality gas fired water heaters deliver consistent warmth without the noise and draft related with forced air systems.
Potential energy savings can be significant. At Automatic Heating we offer free energy usage appraisals, system designs and technical advice. Visit www.automaticheating.com.au