Case Study – Renewable and efficient heating scheme for Olympic-size Swimming Pool

Objectives:

To provide a better swimming experience for customers, it is crucial to maintain a stable pool temperature of 26 degrees Celsius (+/- 2 degrees Celsius) all year round. In addition, at least 40% of the energy used to heat the pool water must come from renewable sources and waste heat recovery systems. A case study of a swimming pool heating system improvement project for a condominium is presented that offers a concept and project brief for retrofitting available heat sources within the building, which can be used as a general reference.
Keep in mind that the heating dynamics of the swimming pool will depend on several environmental, geographical, and construction factors, as well as usage patterns.

• Challenges:
  Frequent breakdown of an existing heating system comprising heat pumps assisted with the electrical heating system.
  With the increase in Occupancy of the residential flats in the condominium, usage of the swimming pools spread over 24/7/365 days.
  During the colder months, swimmers demand a comfortable pool water temperature.
  Repair and replacement of Electric heating elements and mechanical parts of the existing heat pump units is high in addition to the energy cost.
• Assessment of site condition:
  Swimming Pool –
  indoor Olympic-size Swimming Pool
  Indoor Air Change per Hour 6.0
  Inlet Water temperature varies from winter to summer between 100C to 200C.
  Indoor temperature at 27 +/-2 deg C
  Indoor Relative Humidity at 55 +/- 5%
  The condominium has a commercial-grade kitchen operating 24/7/365 days.
  Rooftop clear space is available for solar water heater units.
  Opportunities for decarbonisation and energy efficiency improvement:
  Retrofitting an existing commercial-grade kitchen exhaust system with a waste heat recovery system and using it to heat the pool water.
  Rooftop solar water heater
  Air to Water Heat Pump.
• Project Conception:
  Target:
  To maintain the pool water temperature at 26°C (+/- 2°C) consistently throughout the day and night, every day of the year.
  The rate of change in pool water temperature under operational conditions is around 5 to 7 degrees Celsius in 24 hours.
  The share of renewable energy must be at least 40% of the total energy input for water heating.
  Improve Energy efficiency and reduce Carbon footprint.
  To achieve a Simple Pay-back Period of less than 3.0 Years
  Reduce operating costs.

The heat pumps have been resized and connected in a series to meet the necessary base load for heating the pool water. During periods of high demand, other sources, such as commercial kitchen heat recovery, solar water heaters, and electrical heating units, are utilised to meet the required amount.

• • Each heating source is connected to a series of thermal storage tanks designed to discharge high volumes of water at relatively low temperatures.
    Pool water temperature control:
    The Thermal storage water tanks are installed with demand-sensing hot water recirculation controls.
    Sensors, valves, and actuators are calibrated and wired to the BMS.
    The PID system is tuned to prioritise, schedule, and optimise the operation of the hot water generator network.
    Performance trending is captured and analysed to assess operational demand and respond to requirements within pre-set values.
• Estimates and assumptions.
• The average pool water temperature requirement increase is 5 (+/-) 2 deg C in 24 hours.
  Heating Requirement:
  The demand for heat throughout the year is constantly monitored and referenced to control heat-sourcing systems. The heat pump is specifically designed to meet the base demand load. The Rooftop Solar Heater and the Kitchen Exhaust Waste Heat Recovery system supply the remaining amount.
• Pool Heating Equipment and system integration

Thermal Storage Tank

A thermal storage tank is designed to cater to the heat-up demand load round the clock 365 days. The thermal storage capacity adequately caters to a one-day storage cycle during peak demand load. During off-peak hours, the hot water feed is repurposed in the facility’s service utilities. Sizing of the storage tank, operating strategy, and controlling design would require detailed engineering analysis of hourly and seasonal operational demands.

Inverter Heat Pump (Packaged Air to Water)
The fan and compressor run at variable speeds controlled by the temperature at the thermal water storage tank outlet.
Electrical Coil Heaters assist Heat Pumps in bridging the gap with the set temperature of pool water.
The cascaded heat pump system works with other hot water sources from the rooftop solar and heat recovery system for the kitchen exhaust. This feeds into the thermal storage tank to reduce cycling and maintain stability.

Rooftop Solar Water Heater (Low-temperature commercial application)
A flat Plate Collector type Solar Water Heater is chosen.
Easy to install.
Less affected by environmental conditions (dust, rain, hail, etc)
Durability – estimated 15 years working life.
Efficient heat conversion
Each Flat Plate collector requires an area of approximately 2.0m2 and can heat approximately 100 L water to 600C at an ambient temperature of 140C.

Run Around Coil Exchanger (from Commercial Kitchen Exhaust)
The kitchen exhaust temperature is estimated to be between 40 to 2000C.
Controlled fluid flow is improvised with the ‘Run Around Coil Exchanger’.
Seasonal net efficiency is between 45 to 50%
Heat recovery efficiency is controllable.
Eliminate possibilities of smoke and odour recirculation
Higher cost compared to Heat Wheel recovery system.

• Performance Assessment:
  BMS-controlled operating modes yield the desired outcome.
  Temperature and flow sensors and controllers at the thermal storage tank and across Heat exchangers are calibrated and functional.
  Hourly, daily, and monthly logs are maintained for operational review.
  Prioritization and selection of hot water sourcing meet the requirements of the day.
  Customer Survey is conducted periodically.
• Outcome of Performance Assessment:
  Reduced energy consumption annually.
  Average renewable energy sourcing > 60%.
  Carbon footprint reduced by 50%
  Simple Pay-back period < 2.5 years.
  Improved Customer satisfaction.