HVAC Systems Overview New Marblehead Elementary School at the Bell School Site Marblehead, MA GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.
Life Cycle Cost Analysis HVAC System Options HVAC System Options Overview 1. Baseline: VAV System (ASHRAE Baseline) 2. Option 1: Induction Unit System with DOAS (Dedicated Outdoor Air System) 3. Option 2: Dehumidification Displacement System with DOAS (Dedicated Outdoor Air System) 4. Option 3: Fully Air-Conditioned Displacement System with DOAS (Mixed-Air System) GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.
Goal of Life Cycle Economic Analysis The goal of the mechanical lifecycle engineering economic analysis is to assess the performance of various mechanical systems in comparison to a baseline mechanical system. Each option is compared to the baseline system to determine the lowest combined savings over a 30 year cycle to determine the most advantageous system considering electrical costs, gas costs, maintenance costs, and initial construction costs. By comparison of each option to the baseline system, the option with the greatest total life-cycle savings is generally recommended. To further enhance controllability and overall system performance, additional options should be considered that will enhance year round temperature control and comfort at a possible marginal increase in capital cost. GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.
Variable Air Volume (VAV) System Pros: Cons: • • Lower piping installed costs due to two-pipe system as Moderate noise levels chilled water piping is not required • Reduced temperature control if several rooms • Moderate to high overall installed costs are served by the same V A V unit • • Chiller plant and distribution systems not required Reduced indoor air quality as a result of being a mixed-air system • Low maintenance; no condensate drains, fans, or filters at • terminal units Maintenance of equipment is in occupied area • • Reduced automatic temperature controls installed costs Higher energy consumption due to increased fan resulting from reduced control components energy • Higher energy consumption as summertime use of hot water system is required for hot water reheats of V A V boxes • Overall ductwork costs are greater due to the larger supply and return ductwork systems providing mixed-air rather than ventilation only GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.
Induction Units (Full Air Conditioning) • Ventilation air is provided from high efficiency packaged gas-fired heat/DX cooling RTU w/ ERV • Primary (Ventilation) Air is supplied to plenum and discharges through nozzles • Room air is induced through the heating/cooling coils • Mixture of Primary and Room air is delivered to room through diffuser slots. • Condensate drain pans and piping system for condensate removal GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.
Induction Units Pros: Energy efficient • Ventilation air & ductwork • minimized Low Noise Levels • Flexibility of Installation • Moderate first cost • Simplified Controls (No Fans) • Lower Maintenance (No Terminal • Filters) Cons: Requires increased coordination • with “ceiling” system. (e.g. additional piping, HW , CHW & condensate piping) Requires additional ventilation • air in some cases Increase Energy Consumption • vs. Dehumidified Air Systems GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.
Option 1 – Induction Unit Classroom Section GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.
HVAC System Comparison Mixing vs. Displacement Systems AIR CONDITIONING DEHUMIDIFIED AIR • VENTILATION AIR COOLED BY • VENTILATION AIR COOLED AND SUPPLIED DEHUMIDIFICATION AND REHEATED BY AT 55 DEG F. TO SPACE HOT GAS HEAT RECOVERY TO 68 DEG F. • MAINTAINS SPACE TEMP. AT 75 DEG F. • TEMP. FLOATS IN SPACE WITHIN COMFORT • ADDITIONAL EQUIP. REQD. WITH ZONE INCREASED CAP. TO MAINTAIN 75 DEG F. • REDUCED DUCT SIZES OR NEED FOR • INCREASED DUCT SIZES OR NEED FOR SECONDARY EQUIPMENT ADDITIONAL PIPING SYSTEM • REDUCED CONSTRUCTION COST WHEN • INCREASED CONSTRUCTION COST BY 20% COMPARED TO CONVENTIONAL NON- CONDITIONED BUILDINGS (Dependent upon AC System) • SIMILAR OPERATIONAL COST WHEN • INCREASED OPERATIONAL COST BY 20% COMPARED TO CONVENTIONAL NON AIR (APPROX. $1.75/SF, BASELINE VAV) CONDITIONED BUILDINGS (APPROX. $1.39/SF FOR DEHUMIDIFICATION DISPLACEMENT OR $1.47/SF FOR FULL AC DISPLACEMENT) GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.
Displacement System (Classrooms, Cafeteria, Gymnasium, Corridors) • Ventilation air is provided from high efficiency packaged gas-fired heat/DX cooling RTU w/ ERV • Air is delivered at low velocity and at low levels within the space • The system uses naturally occurring buoyant forces within the space to create a vertical rise of the air throughout the space. Mixed Systems DV Systems E c = 0.8 E c =1.2 - 1.4 • 2-4˚ F differential supply air to space • Supply air rises when heat source is contacted 80°F + • Displaces room air upward 70-75°F • Air rises with pollutants to ceiling 65-68°F • Air returns at ceiling back to air handling GARCIA • GALUSKA • DESOUSA unit Consulting Engineers Inc.
Displacement System Pros: • Excellent pollution removal • Very low noise levels • Very low air velocity • Low moisture levels • Reduced cooling loads • Reduced initial cost • Variable volume reheat is not required • High ventilation effectiveness Cons: • Requires Perimeter Radiation Heating • Does not provide Cooling Setpoint temperature control Displacement Diffuser Options GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.
Displacement System – Energy Conservation Load Calculation Reductions Additional Energy Efficiency Measures & Features • Conventional System: All heat generated in room is included in air flow calculation since • Energy Recovery: Transfers energy from the all airflow is mixed. return air stream to the supply air stream to pre-heat or pre-cool the outside air. • Displacement System: Only loads which occur in the Occupied Zone are factored • Full AC - Variable Air Volume w/ CO2 Demand Control Ventilation: Modulates the • Results in: Smaller equipment & systems airflow to large single zone areas in and lower installed and operating costs for accordance to space mounted thermostat Displacement Systems and CO2 sensors reducing energy consumption due to reduced air changes. Unoccupied Zone Occupied Zone
Option 2 - Dehumidification Displacement Classroom Section GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.
Option 3 – Full AC Displacement Classroom Section GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.
High Efficiency Heating Hot Water and Chilled Water Plant Boiler Plant Chiller Plant • High efficiency (90%+) gas-fired • High efficiency air-cooled chiller condensing boilers • Chilled water temperature reset controls • Boiler temperature reset controls • Variable speed pumps with VFD’s • Variable speed pumps with VFD’s GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.
Building Automation and Energy Management System System (Zone) Scheduling • Occupied-Unoccupied Control • Night Setback Operation • Lighting Control System Integration • Increased Energy Savings • Integrate with Preventative Maintenance • Scheduling
Energy Economics Methodology Energy Economics • Architecture Life Cycle Cost • Weather data • Installation costs Analysis • Building occupancy & • Maintenance cost usage • System Operating Characteristics • Utility Rates Energy Simulation GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.
Energy Model Methodology • Computer Simulation of Building Energy Usage using Department of Energy (DOE-2)/eQuest. • Model consists of project specific: – Architectural features (geometry, orientation, envelope) – Local Weather Data – Occupancy, Lighting, and Equipment schedules – HVAC System Data (specific to each system option) – Local Utility Rates GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.
• Computer calculation of HVAC System economics utilizing NIST BLCC 5. • Calculation factors: – Annual Building Energy Consumption – HVAC System and Maintenance Cost Estimates • Prepared in house using recent project cost data and industry standard estimating references. – Standard Industry Discount, Inflation and Interest Rates GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.
Summary of Results
Recommend
More recommend
