Denver Place North & South Towers Case Study Matt Urquhart Amerimar Realty Management Company Jack Wolpert E-Cube, Incorporated

Denver Place North & South Towers Two office towers, 23- story & 24-story, with 6- story terraces Interconnecting mall on bottom 2 floors of terraces Total of 911,000 square feet in one city block

Denver Place North & South Towers Original Equipment Cooling load served by two 1100 ton electric centrifrugal chillers Electric baseboard space heating Majority of lighting in office towers are standard fluorescent fixtures with magnetic ballasts All electrically powered –need to reduce utility bills, especially demand charges

Denver Place North & South Towers Electricity Use Monthly heating, cooling & other electricity consumption Monthly electricity demand

Denver Place North & South Towers System Work Done Half of electric baseboard heat converted to natural gas hybrid heating system Replace old Energy Management System with new direct digital EMS for hybrid system Installed two flat plate heat exchangers Retrofit existing fluorescent light fixtures Replace electric garage ramp snow melt heaters with radiant gas heaters No chiller work actually performed

Denver Place North & South Towers Hybrid Heating System Tied into chilled water loop Substitutes gas fired heating for electric heating Reduces electric demand charges Used during morning warmup and unoccupied hours for night setback Used for pressurization of outside air during occupied hours 50% of the electric baseboard heaters were disconnected to ensure savings

Denver Place North & South Towers Snow Melt System Formerly an electric system buried in a concrete ramp –high demand load –maintenance and replacement hassles New gas fired radiant heaters –eliminate peak electric demand –hung overhead –use 1.6 times the energy, but gas fueled

Denver Place North & South Towers Lighting Improvements Existing lighting mostly double 34 Watt T-12 fixtures with magnetic ballasts Replace with single 32 Watt T-8 fixtures with electronic ballasts Lighting levels stay the same More than 10,000 fixtures replaced

Denver Place North & South Towers Plate and Frame Free Cooling Two plate and frame heat exchangers installed –work well in arid climates –transfer heat from the chilled water loop to the cooling tower water Allows the possibility of “free cooling” without using the chiller under mild conditions Also decouples the mall and office towers - can now heat and cool these separately if needed

Denver Place North & South Towers Energy Management System Old system controlled lighting and main HVAC functions as a simple time clock New direct digital controls automation system and uses more advanced logic –resets supply air, chilled water, and hot water tempartures re outside air and high zone temperature values –deadband heating and cooling –demand limiting strategies

Denver Place North & South Towers First Cost and Annual Savings of Retrofits Payback period of 7.3 years without rebates

Denver Place North & South Towers Chiller Options Studied Two Existing 1100-ton electric chillers, using R-12 refrigerant –gear teeth failure on one chiller Replace gears and retrofit to use R-134a –various efficiency options studied Use a small gas-fired chiller to reduce peak demand loads Replacement not studied - chillers only 15 years old, with 0.75 kW/ton efficiency

Efficiency not improved much in chiller conversions Small, if any, energy savings, long payback periods Denver Place North & South Towers Cost of Chiller Conversion

Denver Place North & South Towers Small Gas-Fired Chiller Used to eliminate cooling load spike –205 kW for about 100 hours during the year Reconditioned single-effect absorption chiller –annual savings from switch to gas and reduction of electricity demand charges

Denver Place North & South Towers Combining Chiller Work with Other Retrofits Other energy retrofits would have helped finance the chiller work

Denver Place North & South Towers Project Timeline

Denver Place North & South Towers Project Results Energy & operating savings of $182,730 annually Partial replacement of electricity with natural gas for heating Improved tenant comfort in office spaces and main lobbies Improved indoor air quality Savings of retrofits can help to pay for any future chiller retrofit or replacement work