Jiangyin Youtejia Air Treatment Equipment Co., Ltd.

0 Introduction

As energy consumption and environmental concerns—particularly those related to energy conservation and eco-friendliness—become increasingly prominent, coupled with rising demands for higher-quality office and living environments, radiant air conditioning systems and independent temperature-humidity control systems are gradually gaining wider adoption in HVAC applications. Currently, common forms of radiant air conditioning include concrete embedded piping, capillary network systems, and metal ceiling panels, among others. Correspondingly, innovative fresh-air treatment methods have also emerged, such as chilled dehumidification, solution dehumidification, and rotary dehumidification. However, the conventional radiant air conditioning systems currently in use often face various challenges during implementation: slow response times when cooling or heating, relatively low cooling (or heating) capacity per unit area, and difficulties in coordinating with interior design. In contrast, the ceiling radiant panel system for cooling and heating effectively addresses these issues inherent in traditional radiant air conditioning setups, making it a promising technology with even broader potential for future applications.

This article takes the air-conditioning system of a club in Nanjing as an example, introducing the design of a chilled (or heated) ceiling radiant panel system. The system combines rotary dehumidification for fresh air with the ceiling radiant system, enabling independent control of temperature and humidity within the club's air-conditioning setup.

1 Project Overview

The clubhouse is located in downtown Nanjing, spanning two floors. The first floor has a ceiling height of 3.3 meters, while the second floor features a sloped roof. The total floor area is 390 square meters. The building is an existing structure undergoing energy-efficient renovation, and its current function is as a leisure and hospitality clubhouse.

2 Air Conditioning System Types

This project employs independent temperature and humidity control air-conditioning technology, utilizing fresh-air cooling and dehumidification to maintain indoor humidity levels, while high-temperature chilled water (16°C) is used for cooling and temperature regulation. The heating and cooling source relies on a ground-source heat pump system, with rotary dehumidification employed for fresh-air dehumidification, and high-temperature terminal units featuring ceiling radiant panels. This advanced system significantly enhances the precision of indoor temperature and humidity control, further boosting the overall energy efficiency of the air-conditioning system—achieving the dual goals of high efficiency, energy conservation, and exceptional comfort.

3 Design Calculation Parameters

The air conditioning load consists of indoor load and fresh-air load. The indoor load includes both sensible heat load and latent heat load. The fresh-air handling unit handles the fresh-air load as well as the indoor latent heat load; additionally, during peak load periods, the unit can also take on a portion of the indoor sensible heat load. The ceiling radiant system is responsible for managing the indoor sensible heat load.

3.1 Indoor and Outdoor Calculation Parameters

(1) Outdoor Calculation Parameters

Summer: Dry-bulb temperature 34.8°C, wet-bulb temperature 28.1°C; Winter: Dry-bulb temperature -4.1°C, relative humidity 76%

(2) Interior Design Parameters

Summer: Dry-bulb temperature 25°C, relative humidity 50%; Winter: Dry-bulb temperature 20°C, relative humidity 40%

3.2 Energy-Efficient Renovation of Building Envelopes

Energy-saving renovations were carried out on the existing building's thermal insulation: the roof was insulated with 8 cm polystyrene boards, while the exterior walls were insulated with 5 cm polystyrene boards. The exterior windows feature high-transmittance 6 mm Low-E glass paired with a 12 mm argon-filled space and another layer of 6 mm transparent glass, along with thermally broken aluminum alloy window frames and a self-shading coefficient of 0.5.

4 Cooling and Heating Sources & System Design

The clubhouse shares its heating and cooling system with other buildings. The system utilizes a ground-source heat pump, with the primary unit operating at conventional summer supply and return water temperatures of 7/12°C (45/40°C in winter). These temperatures are then further transferred via a plate heat exchanger to provide 16/19°C (42/39°C in winter) to the clubhouse's radiant floor terminals and fresh-air handling units.

The water system is a variable-flow system, and the pumps are equipped with frequency-conversion units that adjust pump frequency based on the pressure difference between the supply and return pipelines. Meanwhile, differential-pressure bypass valves are installed between the main water supply lines to ensure proper system operation even when the pump operates at its minimum frequency.

The system schematic diagram is shown in Figure 1.

 

 

5 Rotary Wheel Humidifying Fresh Air Unit

The fresh-air handling unit features a rotary dehumidification system, integrating a low-temperature regenerative rotary dehumidifier, a direct-expansion evaporative cooling system, and a chilled-water air-cooling system into a single, compact, standalone fresh-air humidity-control unit.

The operating procedure for the fresh air handling unit is shown in Figure 2.

 

 

The fresh air first enters the unit and is cooled by a surface cooler, then passes through the evaporator of the refrigeration system for further temperature reduction. Finally, the low-temperature treated air undergoes dehumidification via a desiccant wheel. After dehumidification, the air is delivered into the room by a supply fan. The fresh air can be cooled as low as 22°C, with a moisture content as low as 7.5 g/kg. Meanwhile, the regeneration air for the desiccant wheel is heated to 45°C simply by passing through the condenser of the refrigeration system, eliminating the need for energy-intensive heating of the high-temperature regeneration air. This unit boasts high energy efficiency, strong dehumidification capacity, and the ability to utilize chilled water from the air-conditioning system, ensuring reliable operation at low running costs.

This project features a fresh-air handling unit with an air flow rate of 2000 m³/h, designed for shared use by the first and second floors. The unit is tasked with managing both the sensible and latent heat loads of the incoming fresh air, as well as adjusting its operation—based on actual conditions—to either handle or bypass the indoor sensible heat load entirely.

This project is a renovation effort. Due to architectural space constraints, the indoor exhaust air cannot be connected to the fresh-air handling unit for heat recovery; therefore, energy recovery from the exhaust air is not feasible. Instead, one exhaust fan has been installed on each of the first and second floors, discharging directly outdoors. The fresh-air fan and exhaust fans are linked for coordinated control.

6 Ceiling Radiant Terminals

This project employs a new type of ceiling radiant system. The ceiling radiant system consists of ceiling radiation panels, manifold pipes, a distribution and collection manifold, a dew-point control system, and more—forming a safe and comfortable cooling and heating system.

This ceiling radiant panel is a standard product with uniform width, while its length can be customized according to specific application needs. The standard product consists of an oxygen-barrier pipe made from De10 × 1.3mm silane-crosslinked polyethylene (PEX-b), securely fixed onto a thin steel plate. During installation, first mount the keel brackets on the ceiling surface, then attach the radiant panel to these brackets, and finally cover it with a layer of gypsum board for the吊顶.

See Figure 3 for the schematic diagram of the radiant panel installation.

 

 

The manifold for the radiant panels is made of De20 × 2.0mm aluminum-plastic composite tubing. The manifold is connected to the radiant coil loops using metal three-way fittings. When connecting the radiant panels, follow the principle of first parallel connection, then series connection—keeping the number of series connections moderate to ensure the total resistance of the radiant panels remains below 2 meters. Ideally, each manifold branch should be connected in parallel to 4 to 5 radiant panel loops, with all loops on the same circuit. Each loop is connected to the manifold’s distribution and collection unit, and no single distribution unit should handle more than 8 loops. Refer to Figure 4 for the specific connection method of the radiant panels.

 

 

This radiant panel is easy to install and can deliver water at a temperature as low as 16°C during summer—lower than that of capillary radiation systems (around 18°C)—resulting in superior cooling capacity and faster response times. Additionally, the radiant panel can be seamlessly integrated with interior decorative panels, minimizing its impact on the overall room design.

This project features functional spaces on the first floor, including a lobby, offices, consultation rooms, massage areas, and a kitchenette. Each room is equipped with either one or two ceiling radiant heating/cooling loops, depending on its size. Additionally, every room includes a thermostat, while the most unfavorable point in each space is fitted with a dew-point sensor—allowing for integrated temperature control and dew-point protection across all areas.

The second floor features a large open space with a pitched roof. Radiant ceiling panels are arranged along the sloping roof, totaling 21 loops connected to 4 manifold units. At the most unfavorable point, 4 temperature control panels and dew-point detectors are installed, enabling precise temperature regulation and dew-point protection throughout the hall.

7 Key Points of Automatic Control

7.1 Room Temperature Control

Each room is equipped with a separate radiant panel circuit, and each circuit features an electric two-way valve. The room also includes a temperature control panel, which regulates the on/off status of the electric two-way valve in the water supply circuit according to the set temperature, thereby maintaining a consistent indoor temperature.

7.2 Indoor Humidity Control

The fresh air damper is controlled by an indoor return-air humidity sensor, opening or closing to its minimum position.

7.3 Indoor Condensation Control

Install a dew-point detector on the room's return line. When the dew-point detector senses that the dew-point temperature is approaching the supply temperature of the secondary water, promptly close the electric two-way valve on that room's return line via the room's thermostatic control panel (equipped with dew-point control functionality). Once the dew-point detector signal is no longer active, reopen the corresponding electric valve on the return line.

7.4 Secondary Side Water Supply Temperature Control

Adjust the opening of the primary-side water supply electric two-way control valve based on the secondary-side water supply temperature sensor.

7.5 Fresh Air Unit Supply Air Temperature Control

Adjust the opening of the electric control valve on the surface cooler of the fresh air handling unit based on the supply air temperature sensor at the unit's outlet.

7.6 Fresh Air Unit and Radiant System Startup Control

When the summer system is running, first activate the fresh-air unit for 10 minutes (the specific duration can be set manually). After 10 minutes, compare the dew point temperature corresponding to the return air’s temperature and humidity with the preset radiant supply water temperature: If the dew point temperature from the return air is 0.5°C lower than the preset radiant supply water temperature, the radiant water pump can be turned on. Otherwise, continue running the fresh-air unit to dehumidify, and re-evaluate after another 10-minute interval.

The winter fresh-air system and the radiant heating system can be operated simultaneously.

8 Air Conditioning System Performance

Once the project was completed and passed inspection, it immediately began operation. So far, it has successfully undergone one cooling season and one heating season under normal conditions. Both indoor temperature and humidity levels have consistently met the design specifications.

During cooling operation in summer, the supply water temperature for the radiant panels is maintained at 15–16°C. The rotary dehumidification fresh-air handling unit automatically adjusts the supply air parameters based on the indoor load conditions, taking on part of the sensible heat load under certain conditions. When the indoor temperature reaches the design setpoint of 25°C, measurements taken across the series-connected maximum number of loops (6 radiant panels) show that the surface temperatures—from the cold-water inlet side to the outlet side of each panel—are as follows: 18.6°C, 19.1°C, 19.5°C, 20.2°C, 20.6°C, and 21°C. As evident, the surface temperatures of the series-connected panels increase progressively with the number of panels. Therefore, it is advisable not to connect too many panels in series during system design, as this could lead to uneven temperature distribution across different zones within the room.

During winter heating conditions, the supply water temperature for the radiant panels is maintained at 41–42°C, while the rotary dehumidification fresh-air unit processes the air to reach an indoor state point with constant enthalpy. When the indoor temperature reaches the design target of 20°C, measurements taken across the longest series-connected circuit (comprising 6 radiant panels) show that the surface temperatures—from the hot-water inlet side to the outlet side of each panel—are as follows: 33.2°C, 32.9°C, 32.4°C, 32.3°C, 31.9°C, and 31.5°C. As expected, the winter scenario closely mirrors the summer conditions, with the surface temperatures of the radiant panels decreasing linearly as the number of connected panels increases.

9 Lessons Learned

9.1 High-Temperature Ground-Source Heat Pump Chiller Units

Due to special circumstances, this project shares the ground-source heat pump unit with other terminal systems, so an intermediate heat exchanger is used to supply 16°C high-temperature chilled water to the radiant system. As a result, the energy-saving benefits of the entire system are not fully highlighted. In similar projects, it is recommended to use dedicated high-temperature ground-source heat pump units, which offer superior operational efficiency and deliver significant energy savings.

9.2 Ceiling Radiant Terminals

The ceiling radiant terminal units used in this project are standard modular products, offering convenient installation, strong cooling and heating capacity, and easy integration with interior design—making them a new type of radiant air conditioning system. In this project (a renovation project where the thermal performance of the building envelope cannot meet the standards of a new construction), these units successfully achieved the designed performance parameters. They can therefore be widely adopted when radiant air conditioning systems are considered for use in new construction projects. However, currently, the product remains relatively expensive, resulting in higher engineering installation costs.

During the system's operation, monitoring of the radiant panel wall temperatures revealed that in circuits with an excessive number of panels connected in series, the temperature at the end wall was nearly 2°C higher than at the beginning during summer. Therefore, it is recommended that the number of panels connected in series should not be too high, as this can easily lead to uneven indoor temperature distribution. Typically, the ideal number of panels in series is one that ensures the radiant panel resistance remains below 2 meters.

9.3 Rotary Dehumidification Fresh Air Unit

This project employs a low-temperature regeneration rotary dehumidifier, which leverages the heat dissipated by the refrigeration system's condenser—specifically at 45°C—to effectively regenerate the rotor. This approach fully utilizes the system's inherent energy, resulting in high operational energy efficiency and significantly reduced running costs. Additionally, based on the project's specific requirements, the system is designed to utilize the available 7°C chilled water, further minimizing the installed capacity of the refrigeration system and lowering the overall investment cost of the equipment.

Since this project is a renovation, heat recovery from exhaust air cannot be considered for the fresh-air system. In the design of similar projects, energy recovery from indoor exhaust air should be taken into account, as it can enhance the energy efficiency ratio of the fresh-air unit and reduce operating costs.

9.4 Summary

The temperature and humidity independent control system, combining a ceiling radiant cooling (heating) system with a rotary dehumidification fresh-air unit, ensures uniform indoor temperature distribution, delivers high comfort levels, and is highly feasible for implementation.

When designing the system, high-temperature heat pump units should be used to enhance operational performance, and plate-type heat exchangers should be avoided for secondary heat exchange, as they can lead to energy losses. Additionally, the fresh air system should incorporate energy recovery from exhaust air to improve the efficiency of the fresh air handling unit.

References

[1] Liu Xiaohua, Jiang Yi, and Zhang Tao. Thermohygrometric Independent Control Air-Conditioning Systems (2nd ed.). Beijing: China Architecture & Building Press, May 2013

[2] Lu Yaoqing, editor-in-chief. Practical Heating and Ventilation Design Manual. Beijing: China Architecture & Building Press, 2008

[3] GB50073-2012 Code for Design of Heating, Ventilation and Air Conditioning in Civil Buildings

[4] Zhao Yirong, editor-in-chief. Concise Air Conditioning Design Manual. Beijing: China Architecture & Building Press, 1998

[5] Compiled by the Science and Technology Development Center, Jiangsu Provincial Department of Housing and Urban-Rural Development. Jiangsu Provincial Guide to Green Building Application Technologies. Jiangsu Science and Technology Press, April 2013.