case study, news
High Efficiency CHW System – Design & Implementation
This case explores the process required to design and upgrade a facility's CHW production efficiency. The process below was taken from a real project for one of SDG's clients.
Project Summary
SDG was involved in both the energy study and design of a chilled water plant system replacement. The project yeilded over $110,000 in annual electric savings, an ROI less than 5 years, with a large incentive from the utility.
Problem & Baseline
The chilled water system for a 413,000 sq. ft. office building consisted of an ice storage approaching the end of its useful life. The ice storage was a source for noise complaints from tenants and also had a very poor efficiency. SDG was involved in analyzing the replacement solution and also designing the new system. The ice harvesting equipment had reciprocating compressors, and provided 650 tons in ice-making mode (at an estimated 1.5 kW per ton) and 900 tons in chilled water mode (at an estimated 0.8-1.1 kW/ton) - for a net peak cooling capacity of around 1,300-1,500 tons.
Proposed
The proposed alternative was to reconfigure the chilled water plant with high-efficiency centrifugal chillers (using chillers with oil-less compressors for the highest efficiency possible) for energy conservation. Three, 450 ton, oil-less chillers were installed. Two new 60-hp condenser water pumps replaced the two existing 40-hp pumps since additional condenser water flow was required for the new system. In addition, four existing 40-hp pumps used for the ice harvesting system were removed along with the existing plate and frame heat exchanger. (Some of the horsepower savings of removing these four pumps were offset by the increase in the condenser water pump power). A custom high efficiency control strategy was developed to reduce equipment load peaks and to maximize equipment efficiencies during operation.
Our Approach
SDG provided pre-purchase engineering services to prepare for preliminary design/scope of work for replacing the chilled water system. This preliminary work was to provide a basis for contractors to provide budget pricing. It included:
- Develop flow schematics
- Determine connection points for chilled/condenser water
- Size new chilled/condenser water piping
- Size/select equipment like chillers and pumps
- Determine preliminary electrical scope and connections
- Outline preliminary sequence of operation and control points
- Prepare and outline scope of work for budget price from contractor(s)
- Attend pre-bid meetings if deemed necessary by the client
After the preliminary design work was completed, SDG then provided design services which included the following:
Review existing/proposed conditions
- Perform a survey of existing proposed conditions and define connection points to new system (included chilled water piping, condenser water pumps, HVAC ductwork, controls, and electrical).
- Lay out proposed chillers and preliminary installation arrangement for discussion of preferred arrangement(s) and potential schedule(s) with facilities personnel. Provide sketches and field visit with selected contractors for planning purposes.
- Lay out proposed piping and ductwork.
- Lay out proposed proposed electrical work.
Draw mechanical and electrical schematics of proposed system
- Demo plan showing removed equipment (both mechanical and electrical).
- Provide updated flow schematic based on selection & design (including, but not limited to chillers, condenser water pumps, piping, insulation, valves, ducting, etc.).
- Provide electrical one-line diagram.
- Designate acceptable/compatible material types.
- Develop a control sequence of operation for new system.
Draw Plan View of proposed Chiller Installation
- Locate equipment.
- Locate piping and connections to existing system.
The last step in the project implementation was to provide engineering services for bidding construction. These included:
RFP Evaluation and Contract Award
- Prepare Design-Build scope for bidding to selected list of contractor(s)
- Contact contractor(s) and ensure attendance at pre-bid meeting
- Attend pre-bid meeting
- Evaluate contractor proposal(s)
- Contact contractor(s) with any questions that may arise
- Reply to any technical questions in reference to contract award (contract to be executed directly between the client and selected contractor)
Construction Administration and Engineering
- Review construction schedule with selected contractor
- Coordinate construction with selected contractor
- Engineering assistance during construction and system startup
- Provide record flow schematic and plan view
- Review operation and maintenance procedures
SDG also worked with the utility to identify incentives for this undertaking. We used a custom and proprietary hourly load/energy analysis to model the system savings. The model included assumptions for building specific data such as envelope construction, occupancy, plug loads, schedules, equipment operation, etc.
Results
The project yielded many positive benefits for the customer.
- $110,138 in electric savings per year
- Monetary incentive from the utility
- Less than 5 year return on investment
- Reduced noise complaints - tenant satisfaction
