A condensing boiler or condensing water heater is a type of boiler which has a much higher efficiency rating than conventional boilers. This improved efficiency is due to the different technology that condensing boilers contain within. In recent years, condensing boilers have become a top choice for replacements and new installs for heating and hot water applications due to their reduced running costs. The rate of energy-saving has even resulted in overseas laws that prohibit the installation of conventional boilers.
How it works
To understand why a condensing boiler is more efficient, you need to know how a conventional boiler works. A conventional boiler has one heat exchanger for the water to pass through. Cooler water from the system enters and collects heat from the boiler flame as it travels through, before flowing off to the heating system or water tank.
The boiler burns fuel to generate a flame. This flame results in the creation of water vapour and carbon dioxide, which, are expelled in gas form through the boiler flue system. Flue gases in a conventional boiler are expelled at a very high temperature which is essentially wasting precious energy. These hot gases are expelled into the atmosphere, causing excess waste.
Why it’s more energy efficient
Depending on the age of a conventional boiler, the typical efficiency rating could be between 70-80% efficiency. To put it simply, there’s a potential for 20-30 cents in the dollar to be wasted through the flue. Condensing boilers were designed to combat energy loss. These boilers are equipped with another heat exchanger to recover the energy that would have been wasted with flue gases. The waste gases travel through this condensing heat exchanger which cools and condenses the vapours into a liquid form which is known as condensate. By transferring vapours to a liquid form, the boiler can extract as much energy as possible out before it is wasted.
The condensing heat exchanger is situated prior to the main heat exchanger in the hydraulic layout of the boiler. The return system water travels through the condensing heat exchanger to preheat before heading through the main heat exchanger. It is common in modern boilers for both heat exchangers to be physically incorporated within one component. So it usually looks like one heat exchanger, but there are actually two forms of heat transfer taking place.
Changing the state of the flue gases and vapours into liquid form occurs when the gas comes in contact with the secondary heat exchanger, which needs to cool the gasses down to at least 55°C to condensate. Therefore, for a condensing boiler to operate in full condensing mode, the return water temperature should be lower than this to achieve the best result. The condensation process should always be considered in the design of a heating system to obtain the maximum benefit from the boiler. Having said that, due to the style of the heat exchanger and the constant developments in condensing boilers, a condensing boiler running at traditional flow/return temperatures of 80/60°C will still achieve about a 4-5% efficiency improvement on a conventional boiler.
With modern control systems and boilers, it is also possible to modulate flow temperatures down when demand is low. For example, a system may be sized at 80/60 (say in a boiler replacement scenario), but if the demand is low, the boiler can alter its flow/return temperatures to make the most of its full condensing mode.
Disposing of the condensate is another important consideration when using a condensing boiler. Condensate discharge is acidic and therefore, corrosive, so it needs to be managed correctly. The best way to do this is to neutralise the liquid with an inline neutraliser before draining. Inline neutralisers give you more options of where you can drain the liquid, and also ensures you are minimising your impact on drains, sewers and the surrounding environment. Hunt Heating offers different sized inline neutralisers, depending on the expected condensate volumes and size of your boiler.
Your new solution from Hunt Heating
The complete shift to condensing technology has already occurred in Europe, and it looks like Australia will follow suit. This shift is more prevalent right now in the Australian commercial market where the savings can be very significant. It makes sense to design an all-new commercial heating and hot water system using a condensing boiler.
It is definitely worth assessing the age, reliability, and efficiencies of any conventional boilers installed in your building. At Hunt Heating, we not only assist with the scope of new projects. We can conduct plant room inspections and assessments on existing boiler plants to see if changing to a new condensing boiler would be beneficial for you and your business.