Pipe Cooler for Poor People

As summer approaches, many people plan to buy new air-conditioners and air coolers. Presently, about 10% households have air-conditioners and 15% households have air coolers. Rest of the population depends on ceiling fans for cooling needs during summer.

• Air-conditioners: Most dependable appliance. It regulates both temperature and humidity under all weather conditions. The user is assured of a very comfortable climate control. ACs are expensive and their usage results in large electricity bills. The conditioned air is circulated in closed rooms; hence oxygen level goes on decreasing. Due to its higher power rating, providing backup during power failures is challenging.
• Air coolers: These work on evaporative cooling principle. Coolers draw outdoor air therefore user always gets fresh air. These are effective during dry heat conditions. When the humidity goes high, its effectiveness is reduced. Due to lower power rating, it is possible to provide power backup during power failures.
• Ceiling fans: Ceiling fans push air in downward direction. The hot air being light, collects near the ceiling of the room. Hence in summer, hot air gets circulated from the ceiling fans, which is not very comfortable. Ceiling fans are affordable and need less power, so it is easy to provide power backup using an inverter.

Proposed ‘Pipe Cooler’ for night time usage

As noted above, 75% households use ceiling fans, which are not very comfortable in summer months. Therefore, there is a need for a lower cost cooler, which will provide better cooling than ceiling fans. Proposed Pipe Cooler provides outdoor cool fresh air after midnight.

Pipe Cooler is easy to fabricate and is affordable. Consumes very low power, hence battery backup can be easily provided. Even those using ACs can switchover to Pipe Cooler after mid night to save power and to get fresh air.

Figure 1 shows the diurnal (24 hours) variation of outdoor (red) and indoor (blue) air temperatures. From the plots it is observed that the indoor temperature variation is in a narrow range. That is because, during day time the building absorbs and stores heat from the sunlight. During night the stored heat is released inside the house. The outdoor air temperature variation is much wider as seen from the figure. In the afternoons outdoor air temperature is high.  After sunset, the air cools down quickly and its temperature goes below indoor air temperature.

From the plots it is clear that, after 1am in the midnight, outdoor air is cooler by few degrees as compared with the indoor air temperature. Fan in the proposed Pipe Cooler sucks outdoor air and directly delivers it to the user without indoor air getting mixed.

Note that the temperature difference mainly depends upon the geographic location. In coastal areas this difference is minimum. In desert areas, nights are cold even in summer, where the temperature difference is higher. Therefore, the results will vary based on the location. But user is assured of outside fresh air which is cooler by few degrees as compared with indoor air.

• Long Pipe: Figure 2 shows the design of Pipe Cooler. It consists of a 110 mm diameter PVC pipe about 6 feet in length. One end of the pipe is fitted with an elbow bend. Dust filter is attached to the other end of this elbow bend. DC cooling fan is mounted on a collar piece. This collar piece is fitted to the other end of the pipe.
• Mounting: Pipe is passed through a window or an opening in the wall of bedroom. Half the length of pipe extends outside. Remaining half projects over the bed near the sleeping position of the user. Pipe ensures that there is no mixing of indoor hot air. The outdoor air is directly delivered to the user. Similarly, outdoor air near the building external wall is warm because of radiation from the walls. To stop mixing of this air, pipe is also extended away from external wall surface by few feet as shown in the figure. The elbow bend is oriented downwards to avoid rain water getting inside the pipe.

Construction

Figure 3 shows the material required. The fan size is 120mm x 120mm x 40mm.

Figure 4 shows the mounting of fan on the collar. Four right angle plastic pieces are cut from two clamps. These 4 pieces are fitted to the collar. The fan is screwed to these pieces as shown in the figure. A small gap of 3 mm is kept between the fan and the collar to avoid fan blades touching the collar. This airgap is closed using tape to avoid air leakage. Finger guard is fixed on the top side of the fan for user safety. Figure 5 shows the fully assembled Pipe Cooler.

Figure 6 shows the interconnection diagram. The adaptor is inserted in a 230VAC socket, which is available in the bedroom. The main switch associated with the socket is used to power ON the adaptor. The +12 VDC output of the adaptor is connected to first terminal of 2way switch. The second terminal of 2way switch is connected to the positive terminal of battery. The pole terminal of 2way switch is connected to first terminal of ON/OFF switch. Second terminal of ON/OFF switch is connected to the Fan. The negative terminals of adaptor, battery and fan are joined together.

• Use: The mains switch is turned ON. The 2way switch is connected to +12 VDC. Now, ON/OFF switch is made ON, the fan starts. In case if the power fails, then the 2way switch is moved to Battery position. Then the fan starts running
  on Battery.

Figure 7 shows the actual wiring. Two switches are mounted in a switch box. A 12V socket is mounted in the same switch box as shown in the figure. The adaptor pin is inserted in this socket. From switch box, two cables are brought out. One for the battery and other for the fan. Fig 8 shows the fully integrated electrical system.

Apart from the above items, a trickle charger is needed. This trickle charger is to be used to charge the battery in the day time, when the cooler is not in use.

• Note: this is a very simple circuit which anybody can easily make. Circuit with automatic switchover to battery when power fails can be designed. For this user has to take professional help. If a user does not want to use battery, then he can directly connect the adaptor 12VDC pin to the fan socket. In that case, the switch box is not required. The wall mounted mains switch in the bedroom is used to operate the fan.
• Caution: It is recommended to use only low voltage DC fans. Do not use fans that operate directly on 230 VAC. As this may be a safety issue, with chances of electric shock. If higher air flow is required, then one can use 24 VDC or even 48 VDC fans (Rexnord Make). These fans will provide higher air flows.
• Installation: Figure 9 shows the view of cooler inside the bedroom. The fan is directed close to the user sleeping position on the bed. It ensures fresh cool air is delivered directly to the user. There is no mixing of indoor hot air.

Figure 10 shows the pipe extending outside the bedroom through the window. The elbow bend is few feet away from the wall. Hence, cool air from the atmosphere is sucked avoiding hot air near the external surface of the wall.

• Design Variations: Design described above is very simple. However, user may want to remove the pipe in the day time if it obstructs movement. Also, aesthetically it may not look good. In that case, one can go for flexible pipes. These pipes could be hidden behind the furniture, etc so that it is not visible. Outside pipe can be rigid and both pipes can be joined together near the window opening. Similarly, one can think of making provision in the wall for fixing the pipe during the construction of building itself.
• Hybrid Solution: Pipe Cooler provides an opportunity for hybrid solution. The AC users can also install Pipe Cooler. During the day time and till midnight they can use AC. After midnight when the outdoor temperature reaches comfortable level, then AC can be turned OFF and pipe cooler can be started automatically. This hybrid solution offers following advantages:
• Power savings due to turning OFF the AC. Reduced monthly bill.
• Fresh air from Pipe Cooler is healthier than stale air from the AC.
• In case of power failure, the Pipe Cooler runs on battery backup.

Figure 11 shows the block diagram of AC to Pipe Cooler switchover logic. It consists of ‘timer OR temperature’ setting circuit. If timer is used, user can set the time delay after which the Pipe Cooler will turn ON in the midnight. If temperature setting is used, then the user can set the outdoor air temperature at which the Pipe Cooler will turn ON. This circuit sends a signal to relay control logic. Relay control logic has a push button that the user presses to turn ON the AC. When the timer/temperature setting circuit gives signal, the relay trips and AC turns OFF. The Pipe Cooler gets powered and the fan starts. In case if power fails, the battery will keep the Pipe Cooler running.

Conclusions

A simple and cost-effective Pipe Cooler for poor people is proposed. It takes in cooler outdoor air after midnight. The long pipe avoids mixing of cool air with the indoor hot air. Therefore, the user gets cool air till the morning. As it needs very less power, battery backup can be easily provided. A hybrid scheme which has both AC and Pipe Cooler is suggested.

Once outdoor air becomes sufficiently cool, then, AC is switched OFF and Pipe Cooler is turned ON. This will save significant amount of electricity and the user gets fresh air. Also, if power fails, the Pipe Cooler runs on the battery power. Thus, Pipe Cooler offers multiple benefits to AC users also.

Vijay Deshpande has done PhD from IIT Kanpur in Electrical Engineering. He has worked in several companies in India. He worked as Technology Specialist and retired from Honeywell India. His current interests include working on cost effective Cooling Techniques and also on Solar Photovoltaic Systems. He has published several research papers in International Journals and published many articles in leading magazines.