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Humidification Is A Gas! - a feature in Energy In Buildings & Industry

Humidification Is A Gas! - a feature in Energy In Buildings & Industry 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 no surprise 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 into an AHU, duct or directly into a room space. This type of unit can leave the facilities manager or building owner burdened with extremely high energy consumption and running costs due to the nature of its operation.

Unfortunately, in some cases, this burden can lead to the unit being turned-off, resulting in poor environmental control and a wasted initial investment in the humidifier.

However, in recent years the development of gas-fired humidification has helped relieve this burden through the economy of using gas rather than electricity. In fact, it is so much more economical, an application that uses around 180kg/h of steam could pay for the replacement of electrode boiler humidifiers with a gas-fired alternative in around one year.

To illustrate this, let’s 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 during the times when the unit would be required, given our climate and seasonal conditions, would equate to a full load running time of 1,321 hours per year.

The typical purchase cost for an electrode boiler of this size would be around £8,000. It would have a power consumption of 137.2kW per hour. The equivalent gas-fired humidifier has typical 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 6 pence per kW, the energy consumption of the electrode unit is £10,874 per year versus just £2,968 at 1.248 pence 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 over five times higher than the gas system - some £5,000 per year versus £1,000. This is due to the fact that replacement boiling cylinders have to be bought on a regular basis for the electrode boiler as they rapidly become caked in limescale due to 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 over a five-year period (see graph).

So if electric humidification is so expensive to run then why is it the most popular type of humidifier system in the UK? Well, humidifier selection is dependent on many variables – initial capital available, acceptable maintenance requirements, available space in plant rooms, etc. Electrode boilers are cheap but as we have already seen, become very expensive, very rapidly. However, they are relatively easy to maintain.

Every steam humidifier will build-up scale as the minerals present in the water are left behind during evaporation. How a humidifier deals with this problem determines how easy it is to maintain. Limescale removal from an electrode boiler is achieved through simply draining the unit, unclipping the boiling cylinder and replacing with another. This is expensive in the long-term but it is quick and simple to do.

Gas units have been notoriously difficult to maintain. Removing the scale on some units can take up to four hours due to 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 and has been designed to make this as easy as possible.

The Neptronic SKG gas-fired humidifier, from JS, can be emptied of scale in less than five minutes due to 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 literally 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 due to the quick release mechanism, is very easy to empty.

Unlike electrode boiler units that are always attached to a wall, gas units are always located on the floor and, until now, have needed considerable amounts of space. It’s not just the footprint of the unit itself to consider, but also the access around it needed for tank removal 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 the EU Directive on The Energy Performance of Buildings coming into effect in January 2006. As particular attention is being paid in the Directive to the CO2 emissions of air conditioning systems, which includes the humidity control, a humidifier which is cost-effective, energy efficient and easy to use is the right product at the right time.

In fact, 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.

Gas-fired technology has been available for humidifiers in the UK for several years now and the cost savings have been a significant benefit for many users. As time has progressed, however, performance improvements have been realised giving better control over output. 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.

Rik Prowen is operations director for JS Humidifiers – the UK’s largest humidification company with the widest range of products, offering a service of advice, design, supply, installation and maintenance. It also offers a comprehensive range of humidifier spares, not only for JS equipment but also for a large range of different manufacturers’ humidifiers, mostly available ex-stock.