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

Garcia Galuska DeSousa, Inc. 370 Faunce Corner Road Dartmouth, Massachusetts 02747-1217

Mitchell Elementary School Bridgewater, MA

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 4. Questions and Discussion

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.

• 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

Dedicated Outdoor Air Systems (DOAS) with Energy Recovery for Ventilation

GARCIA • GALUSKA • DESOUSA

Consulting Engineers Inc.

Mixed Systems

DV Systems Ec= 0.8 Ec=1.2 - 1.4

• 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

• f the air throughout the space.
• 2-4˚ F differential between supply air

temperature to space temperature

• Supply air rises when heat source is contacted
• Displaces room air upward
• Air rises with pollutants to ceiling
• Air returns at ceiling back to air handling unit

70-76°F 80°F + 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

Displacement System – Energy Conservation

Load Calculation Reductions

• Conventional System: All heat generated in room is

included in air flow calculation since all airflow is mixed.

• Displacement System: Only loads which occur in

the Occupied Zone are factored

• Results in: Smaller equipment & systems and lower

installed and operating costs for Displacement Systems

Additional Energy Efficiency Measures

• Energy Recovery: Transfers energy from the return

air stream to the supply air stream to pre-heat or pre-cool the outside air.

• Variable Air Volume w/ CO2 Demand Control

Ventilation: Modulates the airflow to large single zone areas in accordance to space mounted thermostat and CO2 sensors reducing energy consumption due to reduced air changes. 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.

Occupied Zone Unoccupied Zone GARCIA • GALUSKA • DESOUSA

Consulting Engineers Inc.

Displacement Partial Air-Conditioning Displacement Full Air-Conditioning

• Temperature in space within comfort zone;

typically maximum 78°F DB on a design cooling day of 88°F DB / 73°F WB

• Reduced duct sizes or need for secondary

equipment

• Reduced construction cost when compared to

conventional non-conditioned buildings

• Similar operational costs when compared to

conventional non-conditioned buildings (Typically $1.20 - $1.70/s.f.* depending on hours of operation and utility rates)

• Maintains space temp. at 75°F DB, 50% RH
• Additional equipment required w/ increased

capacity to maintain 75°F DB, 50% RH

• Increased duct sizes or need for additional

piping system

• Increased construction cost by approximately

$8/s.f. for area served

• Increased operational cost by approximately

$0.30 - $0.70/s.f. *(depending on hours of

• peration and utility rates)

*(Actual increased installed and operating costs to be determined during SD phase life cycle energy model report)

Displacement Ventilation –Dehumidification versus Full Air-Conditioning

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
• ccupied 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

Pros:

• Low piping installed costs due to refrigerant piping

system only

• Moderate overall installed costs
• Chiller plant and distribution systems not required
• Reduced boiler plant size
• Single cabinet can be utilized for both heating and

cooling applications

• Smaller central ventilation ductwork as only the code

required ventilation air is provided to meet occupancy

• load. CO2 demand ventilation for improved energy

efficiency Cons:

• Individual fan motors in space
• Higher noise levels
• Quarterly filter changes per unit
• More complex automatic

temperature controls

• Condensate drain maintenance for

terminal units

• Maintenance of equipment is in
• ccupied area
• Higher electric energy consumption

due to increased electric heating

• System is proprietary in nature after

installation

• System maintenance requires

technicians w/ refrigeration license.

GARCIA • GALUSKA • DESOUSA

Consulting Engineers Inc.

TERMINAL UNIT HEATING COILS TERMINAL UNIT COOLING COILS

GARCIA • GALUSKA • DESOUSA

Consulting Engineers Inc.

High-Efficiency Gas-Fired Condensing Boiler and Electric Chiller Systems

Options:

• Air Cooled Packaged or Split Condenser
• Water Cooled with Cooling Tower

GARCIA • GALUSKA • DESOUSA

Consulting Engineers Inc.

High-Efficiency Chiller Plant Options

• System (Zone) Scheduling
• Occupied-Unoccupied Control
• Night Setback Operation
• Lighting Control System Integration
• Increased Energy Savings
• Integrate with Preventative Maintenance

Scheduling

GARCIA • GALUSKA • DESOUSA

Consulting Engineers Inc.

Building Energy Management System

Goal of 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 study period to determine the most advantageous system considering… Utility costs, maintenance costs, and initial construction costs. By comparison of each option to the baseline system, the option with the greatest benefit when factoring 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.

Energy Economics Methodology

• Architecture
• Weather data
• Building occupancy

& usage

• System Operating

Characteristics

• Utility Rates

Energy Simulation

• Operating Costs
• Installation costs
• Maintenance cost

Energy Economics Life Cycle Cost Analysis

GARCIA • GALUSKA • DESOUSA

Consulting Engineers Inc.

Energy Model Analysis Methodology

• Computer Simulation of Building Energy Usage using Department of

Energy (DOE-2)/eQuest.

• Model consists of project specific:

– Architectural features (geometry, orientation, envelope) – Lighting Power Density – Local Weather Data – Occupancy, Lighting, Equipment Schedules – HVAC System Data (specific to each system option) – Regional or Actual Owner Utility Rates

• Computer calculation of HVAC System economics utilizing NIST BLCC 5.
• Calculation factors:

– 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.

Example Summary of Results

Conclusions and Recommendations

Upon completion of the life cycle cost analysis study, the system with the highest ownership savings over the 30 year study period is typically recommended while also factoring budget limitations, maintenance requirements, site limitations, thermal comfort conditions, and other factors unique to the project studied.

GARCIA • GALUSKA • DESOUSA

Consulting Engineers Inc.