Rik Prowen, operations director at JS Humidifiers, takes a looks at the
economy of using gas-fired humidification
HUMIDIFIERS can be the most expensive piece of equipment in an air-handling unit, so it is understandable that contractors and ahu manufacturers often look to install humidifiers with a low capital cost in order to keep within budgets. These are very often electrode boiler humidifiers which use electricity to boil water and release steam. However, this type of unit can leave the facilities manager or building owner burdened with extremely high energy consumption and running costs because of the nature of its operation.
In recent years the development of gas-fired humidification has helped relieve this burden. The financial advantages of using gas to power a steam humidifier rather than electricity can pay for electric humidifiers to be ripped out and replaced with new gas-fired units in less than one year.
To illustrate this, let us examine the costs of humidifying an average London office with 180kg of steam per hour in order to maintain a healthy environment at around 50% relative humidity throughout the building.
Operating 12 hours a day, five days a week, would equate to a full load running time of 1,321 hours a year. The typical purchase cost for an electrode boiler of this size would be around £8,000 and it would have a power consumption of 137.2kW an hour. The equivalent gas-fired humidifier has a much higher purchase cost around £21,000 and a power consumption of 180kW.
Given the much higher initial cost of the gas unit, the electrode boiler system seems very attractive, especially to a contractor on a budget. However, based on electrical costs of 6p per kW, the energy consumption of the electrode unit is £10,874 per year versus just £2,968 at only 1.248p per kW for gas. The electrode boiler's energy costs are over four times higher than the gas system.
In addition to this, the maintenance required for the electrode system, including labour and service parts, is more than five times higher than the gas system - some £5,000 per year versus £1,000. This is because replacement boiling cylinders have to be bought regularly for the electrode boiler as they rapidly become caked in limescale because of the minerals left behind during the evaporation process.
Taking all these factors into consideration, installing the initially more expensive gas system provides a payback of around 12 months with savings of £46,530 during a five-year period (see graph).
In the past, gas humidifiers have been notoriously difficult to maintain. Removing the scale on some units can take up to four hours because of difficult access and flat and tubular heat exchangers with scale attached like cement. With the high duties they are designed for, gas boiling vessels are commonly large and can be very heavy when scaled, making handling of the boiling vessel difficult. However, the latest generation of gas-fired humidifiers takes account of the need for maintenance.
For instance, the Neptronic SKG gas-fired humidifier from JS, can be emptied of scale in less than five minutes because of easy access panels and a quick-release mechanism on the boiling tank.
Also, the heat exchanger is a patented spiral design that changes significantly in size during operation. This increase and decrease in size cracks the scale from the surface, keeping the exchanger clean and fully efficient.
The scale that falls off is either flushed away to drain or collects in the bottom of the boiling tank which, because of the quick release mechanism, is very easy to empty.
Its payback time!
Unlike electrode boiler units which are always attached to a wall, gas units are always located on the floor and, until now, have needed considerable amounts of space. It is not just the footprint of the unit itself to consider but also the access around it needed to remove the tank for maintenance. However, a Neptronic SKG with an output of 100kg/h has a footprint of just 61cm by 56cm, with correspondingly small access requirements, making locating a gas-fired humidifier in a plant room now much easier than before.
These improvements in gas-fired humidifier design couldn't have come at a better time with such importance now being placed on reducing carbon footprints. A study by BG Technology has shown that by using a gas-fired humidifier rather an electric unit a reduction in CO2 emissions of 8.2 tonnes per year for a humidifier of around 180kg/h can be achieved.
The Neptronic SKG gas-fired humidifier can be emptied of scale in less then five minutes
Gas-fired humidifier technology has been available in the UK for several years now but in order to gain the financial and energy saving benefits the user did have to suffer with huge units that were difficult to maintain. However, the lessons learned from early generations of gas-fired humidifiers have resulted in modern technology with space-saving design and easier maintenance. The current generation of gas-fired steam humidifiers, such as the Neptronic SKG, allows users to capitalise on the benefits of gas, without any of the previous drawbacks.
JS Humidifiers T: 01903 850200