HOT & COLD FIGURES
Colonel LUONG LAM
Former Chief of Unit 195
President Ho Chi Minh Mausoleum High Command
The air ventilation and air conditioning system of the Ho Chi Minh Mausoleum is a large and comprehensive system. The survey work from the pre-design stage was meticulously carried out, referencing many similar projects both domestically and internationally. The system is equipped comprehensively, and regular maintenance and periodic upgrades are executed according to a tight schedule. The continuous operation for many years has demonstrated the effectiveness and reliability of this technological system. However, due to the impact of the tropical climate and the operational characteristics of the structure, there have been times when the technical system faced disturbances from the environment, exceeding the predicted scenarios and requiring further refinement.
The operational unit, in collaboration with Soviet experts, successfully addressed some complex technical issues right from the early years.
Upon taking over operations, immediate attention was given to resolving any technical malfunctions, large or small, occurring in the technological system. Assigned personnel monitored and quickly identified various issues, regardless of the time, responding promptly to any reports of malfunctions. Whether it was an unusual sound from the shaft bearings, uneven tension of the belts, or erratic signals with seemingly stable parameters, the team investigated and compared direct readings with remote sensing device records, inspecting for irregularities or misalignments. An argument broke out in the main machine room one night due to concerns of a failing motor producing a damaged valve. Despite the 4-meter-high ladder, the team members took turns climbing up to examine. The engine and valve were found to be in good working order, but one contact lug had become trapped on the spring. As a result, the signal light on the display panel showed a valve malfunction.
False alarms occurred on several occasions, but no one hesitated to engage in similar tasks for other occurrences.
The focus was particularly on monitoring any unusual occurrences, especially when multiple issues happened simultaneously. Vigilance extended to assessing the storage capacity to address and resolve these incidents.
Before long, a complex technical malfunction occurred sooner than anticipated: dew formation within the structure and overloading of the main equipment. On Wednesday, September 17, 1975, at 9:20 AM, during the visitation ceremony, an unusual occurrence took place. The hot and humid outdoor air, pressurized, forced its way through the two large doors (facing east) in the center of the building. The volume of air involved was substantial, potentially several times the capacity of the mechanical ventilation system installed in the Mausoleum. Hundreds of square meters of walls, ceilings, and stone floors quickly became cool, causing condensation, water dripping, and forming streams. The strong wind outside, combined with high humidity, led to water puddles throughout the foyer and at the base of the two entrance staircases. The stagnant air carried a strong musty smell, making the environment warm and damp. Even the red carpet, once vibrant, was now swollen and faded due to water retention.
The visitation had to be temporarily halted right outside the Mausoleum. Dozens of comrades from the architectural and hygiene units were immediately mobilized, equipped with mops, pushcarts, chairs, and ladders, swiftly resolving the situation. Fifteen minutes later, the memorial service resumed. However, it had to be repeated again just one hour later.
On that day, the sun wasn't scorching, but the weather was oppressively hot (with relative humidity up to 85%). The strong east wind blew directly into the structure. I observed this situation throughout the morning. As individuals who had experience in design work and teaching about the climate of military construction at the Engineer Corps and the Military Technical Academy, we did not need much time to find the cause but were shocked by the rapid disruption caused by this incident.
In the following week, we revisited the design documents and used measuring instruments to clarify the main and accompanying phenomena. We then focused on finding ways to solve the unusual problem and what needed to be done.
The answer came from the design documentation study: there was no objective of "anti-dew" in the operation task of the four central air-conditioning systems. The issue of countering major environmental disturbances entering the structure was not considered during the original design. That was clear.
The key point at this time was how to solve the "anti-dew" problem. In theory, various factors could be studied:
The Ho Chi Minh Mausoleum is a unique structure. During the memorial service, the main entrance of the Mausoleum had to be fully open (unlike regular structures that can be completely closed).
Therefore, there was a need and a possibility to create an air barrier with the idea of "having a door as if there were no door." The creation of this "soft" barrier would not pose significant challenges for our mechanical equipment, but the external architecture of the Mausoleum would undergo significant distortion. Who could accomplish such a task?
All these were enormous issues at the time (1975-1976). The theoretical solutions outlined had low feasibility. So, no viable solution had been selected!
We believed that, for the time being, there was no feasible measure for preventing dew. However, concerning overloading, we still had to actively increase the cooling capacity of the air-conditioning units. Because the cooling capacity is the dynamic energy to serve regularly and can also resist disturbances. Recognizing this situation, the on-duty expert team at the Mausoleum reported to Moscow. The leading design experts' team arrived in Hanoi two months ahead of schedule to help us solve this significant problem. At the Noi Bai airport, Mr. Ravi (from the Soviet Union) jokingly said, "The cold figures have heated us up."
For several consecutive days, we all worked tirelessly, opening and closing machines for measurements and calculations, engaging in extensive discussions, and then concluding with technical water parameters: the technical water outlet temperature of the air-conditioning units had to be lowered by another 3°C. Only then could we achieve the declared unit capacity. This critical conclusion made us concerned because the water temperature was close to the freezing point. Even a slight oversight could lead to blockages and ruptures of heat exchange pipes. Therefore, additional safety measures had to be implemented.
Lowering the technical water temperature obviously allowed for a significant increase in the cooling capacity of the air-conditioning units.
We also gained valuable insights into craftsmanship skills that combined quantity and quality. Adjusting pressure for specific working areas with short-term anti-disturbance needs, and early cutting off oscillations (and reducing the amplitude of fluctuations) were learned skills. Operators in B32 and F2 rooms had additional operational guides, practical exercises, and enhanced operational skills. Some comrades even took the technician level test ahead of schedule.
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One day, Mr. Ra-vin got a collection of documents I had gathered from the Lang Meteorological Station. The condensed content included statistics on "the frequency of east and southeast winds during the hot season in Hanoi and the average wind speeds in various months."
Although the document was thin, Mr. Ra-vin read it for quite some time, contemplative. He said, "The probability of having winds from the east and southeast is high. We can increase the cooling capacity for the air conditioner, but it's only sufficient to counter low-intensity dew cases. There are still many other factors to consider, including the operational adjustment skills of the operators!" With a smile, he recited a Russian folk song: "Having a small bird in hand is better than waiting for a goose to fly in the sky. Isn't it?"
We all laughed together. Mr. Ra-vin was a seasoned expert with many degrees, having designed numerous structures. He recognized the limitations and the relative achievements quite objectively.
We (the Soviet fellows and our Vietnamese delegation) could not forget the sleepless nights spent together building equipment models and monitoring operations. Our hearts beat in unison when faced with challenging situations and soared with excitement when seeing positive results (the figures on the charts were entirely dynamic and revealing). Those moments, the seemingly alive numbers, created unforgettable impressions.
Since 1990, your technical experts no longer worked at the Mausoleum. Through efforts to rise, the team of scientific and technical officers and operating workers fully mastered the technical aspects of the Mausoleum.
Temperature and humidity parameters, hot and cold figures, the struggles, and the joy of creativity - all these encompass the efforts of fellow workers and engineers across various generations. It also reflects the leadership and management, as well as the camaraderie of friendly allies from times not too distant.
