BRE IP18/00 PDF

Introduction

The phasing out of CFCs and HCFCs (chlorofluorocarbons and hydrochlorofluorocarbons), and uncertainty about the environmental acceptability of the newer HFC (hydrofluorocarbon) refrigerants, has led to growing use of ammonia in air conditioning systems in buildings. Ammonia has excellent refrigeration properties and a low environmental impact. The high efficiency of ammonia-based refrigeration systems could reduce the energy consumption and CO₂ emissions of building cooling systems. However, ammonia is highly toxic and mildly flammable which means that more demanding safety measures are required than with the much safer HFC refrigerants and older CFCs and HCFCs.

Until recently ammonia refrigeration systems were mainly used for industrial applications, especially in the food processing and brewing industries where the advantages of higher efficiency offset the higher cost of safety and maintenance.

The environmental benefits of the use of ammonia must be weighed against the higher safety risks. The Health and Safety Executive (HSE) is concerned^[1] that deficiencies in the underlying management of industrial ammonia systems cause unnecessary incidents leading to injury, deaths and sometimes widespread evacuation of the vicinity. HSE is also concerned that wider use of ammonia could increase the incidence of such occurrences.

Designers and consultants currently believe that a safe location for ammonia refrigeration systems is in the open air on a building roof, based on the premise that because ammonia vapour is less dense than air it should discharge safely skywards. This paper shows that this is an incorrect assumption which can lead to unsafe installations, and it gives preliminary guidance on how to overcome this problem.