Mitchell Elementary School Bridgewater, MA Garcia Galuska - PowerPoint PPT Presentation

Mitchell Elementary School Bridgewater, MA Garcia Galuska DeSousa, Inc. 370 Faunce Corner Road Dartmouth, Massachusetts 02747-1217

Introduction and Agenda 1. HVAC Existing Conditions 2. HVAC System Option Overview – Goals – Displacement System with Dedicated Outside Air Handling Unit System (DOAS) w/ High-Efficiency Heating & Cooling Plants • Options: – Dehumidified (78-80 deg F setpoint) with low humidity (55%RH) – Displacement with Radiant Cooling (75 deg F setpoint, 50-55% RH) – Chilled Water Induction Unit System with DOAS • w/ High-Efficiency Heating & Cooling Plants – Air-Source Variable Refrigerant Flow (VRF) System with DOAS 3. Economic Analysis Methodology Questions and Discussion 4. GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.

HVAC System - Existing Conditions 1. Hot Water Boiler Plant – Standard Efficiency 2. Previously installed Chiller system removed; served 2 pipe system 3. Unit Ventilators - Currently Hot water heating only – Serve Classrooms, Cafeteria/Platform, and Library – Poor Condition; Near end of Service Life – Noisy Operation – Uneven heating and ventilation – High Operational Cost 4. Heating and Ventilation Air Handling Units - Gymnasium - Near end of Service Life 5. Ductless AC Units - Administration Offices - Poor condition; Near End of Service Life 6. Exhaust Air Fans - Majority located in Attic Space - No Energy Recovery; exhaust conditioned general exhaust air 7. Automatic Temperature Controls – Antiquated DDC System GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.

Goals for New HVAC System 1. High Energy Efficiency • High Efficiency Equipment • CO2 demand control ventilation • Energy Recovery • Lowers Operation Costs 2. High Degree of Thermal Comfort 3. High Level of Indoor Air Quality 4. Low Noise Operation – Indoor & Outdoors 5. Reduced Maintenance Requirements • More Central than Terminal “Unitary” Equipment • Fewer filter changes 6. New Building Automatic Temperature Control & Energy Management System 7. HVAC System must fit Architectural/Structural conditions • Ductwork Sizes can vary between system options GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.

Dedicated Outdoor Air Systems (DOAS) with Energy Recovery for Ventilation • Ventilation air is provided from Dedicated Outdoor Air System (DOAS) Air Handling Units • Units located in Attic • Energy Recovery capability allows removal of Exhaust Fans • Hot water Heating and Chilled water Cooling for Highest Efficiency GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.

Displacement System • Ventilation air is provided from high efficiency hot water coil heating/chilled water coil cooling rooftop unit (RTU) w/ energy recovery wheel (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 Mixed Systems DV Systems of the air throughout the space. E c = 0.8 E c =1.2 - 1.4 • 2- 4˚ F differential between supply air temperature to space temperature • Supply air rises when heat source is contacted • Displaces room air upward 80°F + • Air rises with pollutants to ceiling 70-76°F • Air returns at ceiling back to air handling unit 65-68°F GARCIA • GALUSKA • DESOUSA 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 • Requires perimeter radiation cooling to maintain full AC setpoints during peak cooling conditions Displacement Diffuser Options GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.

Displacement System – Energy Conservation Additional Energy Efficiency Measures Load Calculation Reductions • Energy Recovery: Transfers energy from the return • Conventional System: All heat generated in room is air stream to the supply air stream to pre-heat or included in air flow calculation since all airflow is pre-cool the outside air. mixed. • Variable Air Volume w/ CO2 Demand Control • Displacement System: Only loads which occur in Ventilation: Modulates the airflow to large single the Occupied Zone are factored zone areas in accordance to space mounted • Results in: Smaller equipment & systems and lower thermostat and CO2 sensors reducing energy installed and operating costs for Displacement consumption due to reduced air changes. Systems Full AC Option - Supplemental Radiant Cooling Panels : Provide additional cooling without increasing airflow requirements reducing energy consumption due to smaller equipment and fan run time. Unoccupied Zone Occupied Zone GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.

Displacement Ventilation –Dehumidification versus Full Air-Conditioning Displacement Partial Air-Conditioning Displacement Full Air-Conditioning • • Temperature in space within comfort zone; Maintains space temp. at 75°F DB, 50% RH typically maximum 78°F DB on a design • cooling day of 88°F DB / 73°F WB Additional equipment required w/ increased capacity to maintain 75°F DB, 50% RH • Reduced duct sizes or need for secondary • equipment Increased duct sizes or need for additional piping system • Reduced construction cost when compared to • conventional non-conditioned buildings Increased construction cost by approximately $8/s.f. for area served • Similar operational costs when compared to • conventional non-conditioned buildings Increased operational cost by approximately (Typically $1.20 - $1.70/s.f.* depending on $0.30 - $0.70/s.f. *(depending on hours of hours of operation and utility rates) operation and utility rates) *(Actual increased installed and operating costs to be determined during SD phase life cycle energy model report) GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.

Displacement Ventilation – Partial versus Full Air-Conditioning PARTIAL AC FULL AC GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.

Induction (Active Chilled Beam) Units • Ventilation air is provided from high efficiency hot water coil heating/chilled water coil 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 • Low Noise Levels • Flexibility of Installation • Moderate first cost • Simplified Controls (No Fans) • Lower Maintenance (No Terminal Filters) • CO2 demand control for improved energy efficiency 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 System GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.

Variable Flow Refrigerant (VRF) System w/ DOAS • Ventilation air is provided by DOAS air handling units to each space via a sheet metal ductwork distribution system • Terminal indoor VRF units are located within occupied areas to provides zone heating and air conditioning • VRF system uses refrigerant as the cooling and heating medium • The VRF system consists of outdoor condensing units that are connected with refrigerant piping to multiple indoor units. • VRF system can provide simultaneous heating and cooling capability GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.

Variable Flow Refrigerant (VRF) System w/ DOAS Cons: Pros: • Individual fan motors in space • Low piping installed costs due to refrigerant piping • Higher noise levels system only • Quarterly filter changes per unit • Moderate overall installed costs • More complex automatic • Chiller plant and distribution systems not required temperature controls • Reduced boiler plant size • Condensate drain maintenance for • Single cabinet can be utilized for both heating and terminal units cooling applications • Maintenance of equipment is in • Smaller central ventilation ductwork as only the code occupied area required ventilation air is provided to meet occupancy • Higher electric energy consumption load. CO2 demand ventilation for improved energy due to increased electric heating efficiency • System is proprietary in nature after installation • System maintenance requires technicians w/ refrigeration license. GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.

High-Efficiency Gas-Fired Condensing Boiler and Electric Chiller Systems TERMINAL UNIT TERMINAL UNIT HEATING COILS COOLING COILS GARCIA • GALUSKA • DESOUSA Consulting Engineers Inc.