Paving the way for radiant air conditioning using natural energy

In addition to being highly comfortable, the "water-based radiant air conditioning" system is expected to also contribute to energy savings by reducing fan power and easing the temperature of the water supply. However, conventional systems have had issues such as a time lag in room temperature control and the short period during which natural energy can be utilized based on the outside temperature.
The "Dynamic Range Radiant Air Conditioning System" developed here solves this problem through four new technologies, achieving even more comfortable and energy-efficient radiant air conditioning.

1. Pre-cooling cooling tower: Two-stage cooling enables more energy-efficient operation

In water radiant air conditioning, free cooling using a cooling tower is often planned, but in areas where the period during which effective outdoor air conditions are available is not sufficient, a significant energy saving effect cannot be expected. Therefore, by constructing a pre-cooling system that continues to cool the temperature down to the target temperature using a chiller even when free cooling alone is not sufficient, the system can extend the period during which the outdoor air temperature is effectively used.
It has an even greater effect when combined with the VWV-VT control described below.

2 Return water temperature cascade control: A mechanism for controlling the temperature of water rather than the room temperature

Water-type radiant panels often control room temperature by adjusting the flow rate of hot or cold water passing through the panel depending on the room temperature at the time. However, because there is a delay between when the flow rate is changed and the room temperature responds by changing it, the flow rate can be repeatedly increased or decreased too much, resulting in an unstable control state.
Therefore, we focused on the correlation between the "capacity of the radiant panel (amount of heat dissipation)" and the "return water temperature of hot and cold water (the temperature of the water that returns through the panel)." We developed a method to determine the return water temperature linked to the required heating and cooling capacity from the indoor temperature measured by a sensor, and to control the flow rate to achieve that temperature. Because the return water temperature changes without delay in response to flow rate control, by replacing the indoor temperature control target with the return water temperature, it is now possible to control room temperature without time delay even with a water-type radiant panel.
This method of replacing the original target value of automatic control (room temperature) with another target value that has some correlation (return water temperature) is called "cascade control."

3 VWV-VT control: Combines the benefits of "flow rate" and "temperature"

The return water temperature set point determined by cascade control in ②, for example in cooling operation, becomes higher as the load decreases. The third technology that is the basis of dynamic range radiant air conditioning lies in making effective use of this characteristic.
Conventional variable water volume (VWV) control, which changes the flow rate according to the air conditioning load, is effective in reducing the pump's power consumption, but the reduction effect drops drastically when the load is medium or lower. Therefore, we switched to variable temperature (VT) control, which raises the supply water temperature according to the return water temperature when the load is medium or lower, and developed and introduced VWV-VT control, which aims for the best balance between variable water volume and temperature.
This control not only reduces the power required for transport, but also enables cooling at a lukewarm water temperature compared to conventional radiant air conditioning control, improving the COP of the chiller and further expanding the use of pre-cooling cooling towers, resulting in significant energy savings and utilization of natural energy.

4. Heat exchanger-less piping system: Direct transmission from the heat source to the panel reduces energy loss

「新菱神城ビル」では熱伝達効率の高い樹脂管を用いた水放射パネルを採用しています。
樹脂管は空気中の酸素を透過してしまうので、空調配管や熱源機器に金属腐食を生じさせてしまいます。そのため、水放射パネルは熱源系統とは熱交換器を介して構築するのが一般的であり、熱交換によるエネルギーロスのせいで、熱源水温のポテンシャルが100%活用できていませんでした。
そこで本計画では、①腐食促進イオンを無害化できるアニオン交換樹脂に透過させた熱源循環水を用い、②脱気装置を設けて運転中に配管内に浸入した溶存酸素を除外することで、熱交換器レス配管システムの構築を実現しています。

By combining the above four technologies and dynamically varying the supply and return temperature range, the entire system provides high comfort and energy savings.