Consulting-Specifying Engineer - August 2008 - (Page 38) Gas consumption, boiler output, Btu 70 2 million 60 Outdoor temperature, F 1.5 million 50 40 1 million 30 20 500,000 10 0 6 a.m. 9 a.m. 12 p.m. 3 p.m. 0 6 p.m. Time (Jan. 16, 2006) Existing boiler peak delivery, Btu/hr Proposed boiler peak delivery, Btu/hr Gas consumption rate, Btu/hr Estimated load-low end Estimated load-high end Outdoor temperature Figure 1: Graphical representation of the estimated loads of the existing boiler and the proposed replacement. Source: David Sellers 2.50 Learning from experience Mining the data from your building can be a powerful technique for guiding ongoing O&M, and we had used it before on the facilities chilled water plant as shown in Figure 2. The red line in Figure 2 represents the overall plant kW per ton at different load conditions when Marriott Retrocommissioning Commissioning (MRCx), Marriott’s own brand of retrocommissioning, was first started. The full load kW per ton was satisfactory but the part load performance was disappointing, especially when the team realized that its plant actually spent a lot of time operating at 250 to 400 tons. But the team identified and implemented an improvement that reduced the condenser and evaporator pump energy, shifting the plant’s profile to the green line. The opportunity was identified by testing the exiting pumps at full load and part Pre MRCx original plant kW per ton 2.00 Modified plant kW per ton, option 1 Post MRCx original plant kW per ton Overall plant kW per ton Modified plant kW per ton, option 3 1.50 1.00 0.50 0.00 0 100 300 300 400 500 600 700 800 900 1,000 1,100 1,200 1,300 1,400 1,500 1,600 Load, tons Figure 2: San Diego Marriott Hotel and Marina historical and anticipated chilled water plant kW per ton. Source: David Sellers 38 Consulting-Specifying Engineer • AUGUST 2008
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