Development of High-Performance Direct Expansion Systems Compatible with New Refrigerants

Mikikai Corporation (President: Kazuhiro Nagoya) has constructed a low- and high-temperature environmental wind tunnel facility within its comprehensive training and research facility, the 'Mikikai Techno Center,' and will begin full-scale operations in June 2026.

Background and Purpose

The company has delivered numerous environmental test systems, primarily for the automotive sector, capable of temperature control in low-temperature ranges (down to -40°C). For environmental test systems with significant thermal load fluctuations, wide temperature and humidity control ranges are required, along with high control accuracy and temperature distribution uniformity.

While the company has a track record of supplying direct expansion (DX) systems using refrigerant R404A (GWP 3,920), this refrigerant is subject to manufacturing and usage restrictions under the 'Act on Rationalization and Proper Management of Fluorocarbon Use' (Fluorocarbon Emission Reduction Law).

Given this context, the company believes that direct expansion cooling systems (DX systems) using green refrigerants—those with zero ozone depletion potential and low global warming potential—are a strong alternative for achieving carbon neutrality and reducing environmental impact.

This facility incorporates a DX system using the low-GWP refrigerant R448A (GWP 1,390) and a system using the natural refrigerant carbon dioxide (CO2) (GWP 1).

Facility Overview

The facility features a Göttingen-type wind tunnel (with both open and closed configurations) installed in a test chamber measuring W8,700 × D3,000 × H3,250 mm.

Image of the constructed low- and high-temperature environmental wind tunnel facility

Main Performance Specifications:

Temperature Range: -40 to +50°C DB

Humidity Range: 20 to 90% RH

Vehicle Wind Speed: 0 to 200 km/h (acceleration/deceleration up to 0.3 G)

Development and Verification Content

The test chamber employs the company's proprietary Dry Shell® method. By maintaining a low dew point environment inside, parts of the ductwork and cooling equipment do not require insulation, and the internal structure allows visual inspection through glass or acrylic materials. This achieves high verifiability, enabling direct visual confirmation of the equipment interior even in a low-temperature wind tunnel.

Dry Shell® Appearance

The newly constructed facility enables verification of the following:

1. Dynamic characteristics of low-GWP refrigerants: Detailed measurements across various points, including temperature distribution on the cooling coil surface of non-azeotropic refrigerants

2. Temperature stability under rapid load changes: Feedforward control based on vehicle wind speed and introduction of cold storage tanks

3. Temperature distribution on cooling coil surfaces: Implementation of the company's unique special equal distribution mechanism

4. Controllability in high-temperature and high-humidity environments: Verification of appropriate control valve selection and capacity control according to temperature requirements

5. Energy reduction: Verification of reduced reheat heater and humidifier steam usage through the above measures

Future Outlook

By utilizing this test chamber, the company aims to establish DX systems using new refrigerants and advance high-performance environmental test systems. This will expand sales efforts to customers requiring environmental chambers, particularly in the transforming automotive industry.

※Dry Shell®: An air conditioning technology that maintains low-temperature environments without sealing penetration points by dehumidifying the surrounding area of cold rooms.