1. Types of Cooling and Heating Sources
(1) Chilled/Hot Water Units
1. Electric Compression Chillers/Heaters
- (1) Reciprocating
- (2) Scroll
- (3) Screw
- (4) Centrifugal
2. Lithium Bromide Absorption Chillers/Heaters
- (1) Steam-powered
- (2) Hot water-powered
- (3) Direct-fired
(2) Heating Sources
- 1. Electricity: (1) Electric furnace, (2) Heat pump
- 2. Fossil Fuels: Gas, oil, coal
- 3. Renewable Energy: Solar, geothermal, river water, industrial waste heat, residential waste heat
(3) Heat Pumps
Heat pumps transfer heat from outdoor environments to indoor spaces, providing heating in winter and cooling in summer.
2. Advantages and Disadvantages of Different Systems
(1) Chiller + Heat Exchanger
Concept: Uses a chiller for cooling in summer and a boiler or district heating system for winter heating.
Advantages:
- Lowest initial investment among centralized systems
- Lower operational costs than steam-powered lithium bromide systems
- Longest lifespan (23 years per ASHRAE standards)
- Centralized system simplifies maintenance Disadvantages:
- Large system, difficult for individual metering and control
- Requires a sizable mechanical room and extensive piping
- Cooling towers generate noise and impact aesthetics
(2) Air Source Heat Pump
Concept: Extracts heat from outdoor air for heating in winter and rejects heat to outdoor air for cooling in summer.
Advantages:
- Dual-purpose system, eliminating the need for a separate boiler
- Saves water and energy due to a high efficiency ratio (~3)
- Compact structure, no cooling tower needed, reducing space and maintenance costs
- Outdoor installation saves indoor space
- Modular design enables flexible zoning and operation Disadvantages:
- High noise levels
- Reduced heating efficiency in humid winter climates due to frequent defrosting
- Less reliable than chillers, with higher failure rates in extreme conditions
- Shorter lifespan due to outdoor exposure and environmental factors (e.g., acid rain corrosion)
(3) Steam-Powered Lithium Bromide Absorption + Heat Exchanger
Concept: Uses waste steam from power plants for both cooling and heating.
Advantages:
- Environmentally friendly, reduces greenhouse gas emissions
- Reduces peak electricity demand, lowering utility costs
- Safe low-pressure operation
- Minimal noise and vibration
- Wide modulation range (20%-100% capacity)
- Utilizes low-grade waste heat effectively Disadvantages:
- Higher overall energy consumption than electric chillers
- Large footprint and heavy equipment
- Requires extensive cooling water infrastructure
- High vacuum integrity required for performance maintenance
- Corrosion issues with lithium bromide solutions
(4) Ice Storage + Heat Exchanger
Concept: Stores thermal energy during off-peak hours and releases it during peak demand.
Advantages:
- Reduces peak electricity demand
- Decreases chiller size and electrical infrastructure costs
- Takes advantage of electricity price differences
- Low-temperature chilled water (1-4°C) enables efficient air distribution
- Enhances air quality and comfort Disadvantages:
- 20-40% higher initial investment than conventional systems
- Requires significant space for ice storage
- Lower chiller efficiency during ice-making mode
- Complex design and operation
(5) Variable Refrigerant Flow (VRF) System
Concept: Uses a variable refrigerant flow system to efficiently control indoor temperatures across multiple zones.
Advantages:
- Small refrigerant piping makes installation flexible
- Allows for independent control and metering per tenant
- Eliminates large mechanical rooms
- Enables phased installation to reduce upfront investment Disadvantages:
- Higher initial investment than traditional systems
- Shorter lifespan than centralized systems
- Insufficient heating capacity in extreme cold
- Complex refrigerant piping increases leakage risk
- Uneven airflow distribution reduces comfort
(6) Ground Source Heat Pump (GSHP)
Concept: Extracts heat from the ground, water bodies, or underground water.
Advantages:
- Utilizes renewable energy with 30% lower operational costs
- Environmentally friendly with lower emissions
- Long lifespan (~20 years)
- Flexible installation and independent control Disadvantages:
- 10-20% higher initial cost than traditional systems
- Requires thermal balance in the ground to maintain efficiency
- Limited research on long-term ground heat accumulation effects
(7) Water Loop Heat Pump
Concept: Uses a water loop for heat exchange, transferring energy between heating and cooling zones.
Advantages:
- Energy-efficient, reuses heat within the building
- Lower initial investment, no need for large mechanical rooms
- Allows for independent metering and flexible installation Disadvantages:
- High noise levels for units over 10 kW
- Requires dedicated fresh air supply system
- Hidden installation makes maintenance challenging
- Higher electrical load than traditional central systems
(8) Room Air Conditioners
Concept: Decentralized units suitable for residential and small-scale office use.
Advantages:
- Lowest initial investment due to market competition
- Low operating costs with independent control
- Simple to install, operate, and maintain
- Quick temperature adjustments with inverter models
- Useful as a supplementary system for frequently occupied areas Disadvantages:
- Poor indoor air quality due to lack of fresh air intake
- Aesthetic issues with visible outdoor units
- Uneven airflow distribution
- Inadequate heating in winter
- Condensate drainage issues
- Heat interference between stacked units (“frog leap effect”)
Conclusion
Each cooling and heating source has unique strengths and weaknesses. The choice depends on factors like initial investment, operational efficiency, environmental considerations, and site conditions. Proper evaluation is necessary to ensure an optimal balance between cost, performance, and sustainability.