Since 1974, DWD International has designed, manufactured, installed and maintained HVAC and pressurization systems that withstand the most challenging conditions. DWD was one of the first companies to offer explosion-proof, corrosion-resistant HVAC equipment, and we continue to lead the industry with innovative designs and quality equipment. In 1990, DWD pioneered a variable frequency drive (VFD) pressurization unit that offers 100% stand-by in a single cabinet, minimizing outside-air loads while still meeting NFPA 496 standards.