Peltier elements – cooling and heating

Recommendation points

• How to make your own water cooler
• How to make a mini-refrigerator, chiller or air conditioner on thermoelectric modules on your own
• Where else are thermoelectric modules used?

Standard thermoelectric modules have an inverse operating principle. In this article, we will talk about the use of Peltier-Seebeck modules in heat exchangers and give an example of assembling a water cooler and a basic cooling system for air with the possibility of restarting (heating).

The principle of operation of thermoelectric modules (TEM), used for cooling, is based on the Seebeck effect – the opposite process relative to the Peltier effect. The main element is the same TEM described in the first part. When direct current is applied to the field of thermocouples, a temperature difference is observed on the planes of the ceramic plate. This is a fact based on a thermodynamic process, which we will not describe (so as not to tire of scientific calculations), but we will show how to apply it in everyday life..

Note.To build the units, instructions for which are given below, you will need basic practical skills in assembling electrical circuits. The given models of nodes are approximate and can be replaced by similar (or more / less powerful) at the discretion of the master.

How to make your own water cooler

The discerning reader has already understood that the “miracle ladle” from the first part can be used to cool the liquid if you run it “in the opposite direction” by connecting a direct current.

TEMs are used in every water cooler. It is quite possible to build an analogue of this factory device with your own hands, while it will work no worse. We will describe the very principle of operation and the assembly scheme. The layout and execution options can be selected based on your own needs. For example, make it portable or stationary, integrated into kitchen furniture or a drinking water treatment system. The latter option is optimal, since the cooling in the system will be controlled (upon power supply).

For this we need:

1. Rectangular flat sealed stainless steel container with dimensions 100x100x30 (flask-heat exchanger) with threaded outlets on? inches on the short sides. This is the only element, the manufacture of which is best ordered by a craftsman at the factory..
2. Drinking water supply with fitting on? inches (from a container or plumbing).
3. 10-12 volt power supply with adjustable amperage.
4. Thermoelectric modules TEC1-12705 (40×40) – 2 pcs..
5. Wire cross-section 0.2 mm.
6. Hot melt glue or thermal paste.
7. Key for 2 channels (toggle switch, button).
8. Faucet, soldering iron, solder.

Using hot glue, fix the TEM on the flask. We connect the wires in the appropriate groups (plus and minus). We determine a convenient location for the key, taking into account the possibility of replacement during repair and accessibility during use. We include it in the diagram. We connect the wires to the power supply. We carry out circuit tests.

Attention! When testing, limit yourself to observing the very fact of correct operation, but do not try to give the maximum load dry – this can lead to failure of the TEM (cannot be repaired).

Then we connect the inlet fitting of the heat exchanger flask with the water supply channel, and the outlet with the hose (flexible or rigid) to the tap.

We fill the system with water and set the optimal amperage at the required jet pressure. The optimal head is slightly stronger than gravity. This will be enough for the intake of cool drinking water. The rest of the nuances – fasteners, wire length, location – are purely individual in each case.

This basic system can be developed and improved. For example, install a thermostat in the heat exchanger and include it in the circuit instead of a key (toggle switch) – it is suitable where water of a certain temperature is constantly needed. The heat exchanger flask can be made of silver for additional water ionization. By including a step-up converter of constant voltage EK-1674 in the system, you can reduce power consumption to a minimum.

Calculating the cost of building a cooler:

Name	Unit rev.	Qty	Unit price / rub.	St, rub.
Stainless steel heat exchanger (with work)	PCS.	1	1000	1000
TEM TEC1-12705 (40×40), 53 watt	PCS.	2	300	600
Power Supply	PCS.	1	300	300
Key	PCS.	1	50	50
0.2mm wires	m	five	6	thirty
Hot glue (thermal paste) Radial 2 ml	PCS.	1	150	150
Pipes, fittings, liners	–	–	300	300
Total				2430

This system does not use a finned radiator, since the set goal – cooling (but not freezing) a small volume of water (300 ml) – is achieved without it..

How to make a mini-refrigerator, chiller or air conditioner on thermoelectric modules on your own

A more difficult task is air cooling. If in the case of water, the efficiency of the cooler is guaranteed by the difference in the density of the media (water – air), then in the case of a homogeneous medium (air – air) the situation is more complicated. The main difficulty is the removal of temperature from the hot side of the TEM surface. More precisely – synchronous temperature removal from both surfaces. If you just start the Peltier-Seebeck element, the heated and cooled air will mix, and the temperature will equalize.

In confined spaces of small volume (up to 0.7 m³) a cooling system based on a TEM with a double-sided air outlet is quite applicable. This allows you to build a new cooling box or give a second life to an old refrigerator (freezer). To do this, you will have to slightly complicate the system by including a pair of exhaust fans of mutual power, a temperature relay, a finned radiator and use more efficient thermoelectric modules.

We need (for one base cooling point):

1. TEM TES1-12712 (40Х40), 106 watts – 1 piece.
2. Fan RQA 12025HSL 110VAC (or more powerful) – 2 pcs.
3. Radiator HS 036-100 (100x85x25 mm).
4. Thermostat TAM-133-1m (temperature switch with sensor).
5. DC Power Supply 12 Volt, 6 Amp (Adjustable).
6. Duralumin sheet.
7. Wires, thermal grease, fasteners

In the finished box, in the upper part of the refrigerated zone, we make a rectangular window with dimensions of 100×100 mm. We cut out two duralumin plates with dimensions of 130×130 mm and 180×180 mm. We fix the fan in the center of the smaller plate in such a way that the airflow remains 1 cm. We install the temperature switch inside the box. We mount the smaller of the plates from the inside of the box (with a fan inside the box) onto screws or rivets through a sealant. We glue the TEMs on the mounted plate and bring out the wires. We cut out and bend a large plate so that it fits into the mounting hole, but at the same time there are sides for fixing to the box wall from the outside. We attach a radiator and a second fan to it. Lubricate liberally with TEM thermal paste and mount the plate to the box wall through a sealant.

Attention! There must be a maximum contact between the TEM area and the plate!

We collect the electrical circuit. We recommend turning on the fans at a constant maximum power, and the current for the TEM through the regulator. This will ensure effective temperature removal and air mixing when operating in different modes (not at full capacity).

The advantages of this design:

• silent operation in comparison with compressor refrigerators;
• lack of mechanisms and moving parts, frictional forces (nothing to break);
• liquid heat carriers (freon) are not used;
• total power consumption of about 200 watts;
• you can upgrade the design, vary the performance;
• availability and maintainability of individual units.

Disadvantages:

• condensation may appear on the duralumin plates;
• external control unit;
• many factors and nuances of work are revealed empirically during use;
• small scope.

Calculating the cost of building a basic cooling system for a refrigerator and air conditioner:

Name	Unit rev.	Qty	Unit price / rub.	St, rub.
TEM TES1-12712 (40X40), 106 watts	PCS.	1	600	600
Fan RQA 12025HSL 110VAC	PCS.	2	150	300
Duralumin 3 mm	PCS.	1	300	300
DC power supply	PCS.	1	300	300
Thermostat TAM-133-1m	PCS.	1	250	250
Radiator HS 036-100	PCS.	1	220	220
Wires, thermal grease, fasteners, solder	–	–	300	300
Total				2270

In principle, this design is a ready-made built-in air conditioner that can be installed in the cab of a car, tractor, in a closed aviary or in a security booth. You just need to think over the constructive protection against atmospheric precipitation.

The power reserve of the TEC1-12712 module is quite large. The temperature amplitude on the sides of the element can reach 50 degrees. At an air temperature in the room of +27 ° C and the use of a liquid cooling system (radiator + fan), you can extract an impressive minus 25 ° C at the outlet! This allows you to create compressorless and quiet freezers even at home.

Where else are thermoelectric modules used?

The Peltier-Seebeck effect has been known since the 1840s. It is actively used to this day, thanks to the stability of the laws of physics. The thermoelectric module will always find a place where there is excess energy or it is necessary to quickly and silently transfer heat.

The main applications of thermoelectric modules:

1. Cooling of microcircuits. Fans are a thing of the past as the main heat exchanger. They are being replaced by compact, silent and practically eternal TEM.
2. Mechanical engineering. Even the most modern ICE generates exhaust gases from the combustion chamber. Engineers use their heat to generate additional energy using Peltier elements. The collected energy is fed back to the engine systems, but in the form of direct current, which saves fuel.
3. Appliances. Everything described above, plus most household appliances that work for cooling or heating (except for compressor refrigerators).

And one last little secret. Our module has an almost wonderful property – reversibility. This means that when the DC polarity is reversed on the module wires (using a switch), the hot and cold surfaces are reversed. The cooler turns into a heater, the refrigerator into a thermal chamber (incubator), and the air conditioner into a low-power fan heater. You don’t have to change the device schema for this. Simply change the polarity.

This principle is used in a device called a recuperator. It is a box, consisting of two isolated chambers, which are connected with each other using fans. With the help of Peltier modules, the cold air from the outside is heated by the energy extracted from the heated air that is removed from the room. The device allows you to save on heating the house.