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Reznor Advances The Performance of Warm-Air Heaters

The latest generation of Reznor’s industrial gas-fired unit heaters has reached new levels of efficiency. Called the RHeco range, the efficiency of these condensing units at minimum load (modulating down to 20%) is 109% net. Full-load efficiency is 100% net. Such high efficiencies enable these heaters to qualify for Enhanced Capital Allowances and achieve a favourable payback period compared with conventional heaters.

Simon Garratt, marketing manager, summarises the range: ‘Following years of extensive research and development, we’ve created the next generation of industrial gas-fired unit heaters.’

There are five models in the range with outputs from 25 to 100 kW and airflows from 3590 to 10 617 m3/h.

The development of this range was driven by the demands of recent and forthcoming European legislation, especially the ErP (Energy related Products) Directive, Lot 21 of which includes gas-fired warm-air heaters. Such products have been required to have low NOx emissions (less than 25 ppm) since 25 September 2013 and low carbon-monoxide emissions (less than 20 ppm).

Tier 1 of Lot 21 comes into effect in 2017, with Tier 2 following in 2019. That is a long way ahead, but it has been characteristic of manufacturers (pumps are a well known case in point) to be years ahead of the requirements of the ErP Directive and then encourage the wider industry to match their pace by specifying and installing such products.

The RHeco range has a number of innovative features. They include a new design of heat exchanger, premix burner and what is claimed to be a unique pull-through configuration with a patent pending. One benefit of the pull-through configuration is to prevent the risk of flue gases leaking into the heated space if a crack develops in the heat exchanger, as required by legislation in some European countries. The loss of pressure will ultimately lead to the burner shutting down.

But it is the heat exchanger that immediately attracts attention as an integrated unit with sections for sensible and latent heat. Starting from the burner in the bottom right-hand corner of the illustration, the combustion gases pass through a series of tubes with two hairpin bends and three right-angle bends. The combustion gases then pass through the stainless-steel condensing heat exchanger, with several changes of direction to maximise heat recovery.

The pull-through fan is a specially modified unit from ebm-papst with a plastic impeller designed to cope with pH4 condensate. The impeller is balanced by drilling holes in it rather than adding weights. There is a drain hole in the fan unit for condensate.

Air from the space to be heated is driven across the heat exchanger (right to left) by a Ziehl-Abegg fan with Owlet axial impeller blades for energy efficiency and low sound levels.

The flue and air inlets can be horizontal or vertical. A balanced-flue arrangement is also available.

There are two control options. One is Opentherm bus communication. The other is 0 to 10 V.

Reznor’s plans for the future development of these unit heaters include a range with centrifugal fans followed by a ducted version