Outlined below is a simplified selection procedure devised to take the guesswork out of choosing the proper TEC and to allow the user to obtain initial designs and estimates of performance for a single or two-stage thermoelectric cooler. Because of the non-linear behavior of thermoelectric coolers and the

number of variables involved in analyzing them, they can be designed and modeled more accurately by our experienced engineers using Marlow Industries' internally developed computer software. For selection of a thermoelectric cooler with more than two stages, or if more precision is required, please consult one of our application engineers. Once the decision to use a thermoelectric cooler has been made, the actual selection of a suitable thermoelectric cooler is relatively simple. The following information outlines a step by step procedure that will take you through determining your heat load, required DT, and the number of stages required to meet the DT.

Once you have completed the analysis you will have narrowed the field of suitable TECs to two or three. You may then proceed to the next section to performance of the selected TECs within your application requirements.

Proceed to "Estimating TEC Performance"

1. Calculate Heat Loads

* Refer to section entitled "Estimating Heat Loads" for information on determining these loads.

2. Define Temperatures

3. Determine Number of Stages Required

Select the minimum number of stages from the table below which will meet the required DT.

In this example, a single-stage TEC will suffice, since 64°C is greater than the desired 35°C DT. If the number of stages required exceeds two, the following selection process is not applicable. These calculations are only accurate for a one- or two-stage thermoelectric cooler. For three-stage and above, call one of our applications engineers for assistance.

4. Select an Appropriate TEC

The performance graphs used in this brochure have been normalized to provide a universal curve for use with any single- or two-stage TEC for which the "Maximum" values are known. By using ratios of actual to "Maximum" performance values, performance may be estimated over a wide range of operating conditions.

a. Determine the ratio of DT/DTmax.

b. On the performance graph (Figure 2), draw a horizontal line on the graph corresponding to DT/DT_max (.55 in this example).

c. Obtain the Optimum value of Q/Q_max at the intersection of the horizontal line just drawn and the diagonal Optimum Q/Q_max line. Interpolation between curves may be necessary.

d. Obtain the Maximum value of Q/Q_max at the intersection of the horizontal line (drawn in step 4b) and the right vertical axis.

e. Divide the total heat load (from step 1) by the Q/Q_max ratios above to calculate the Optimum and Maximum Q_max.

f. Select a TEC from Marlow's standard product list with a Q_max greater than the Maximum Q_max (20 watts in this example), but less than the Optimum Q_max (36 watts in this example). Keep in mind that within this range a TEC with a Q_max close to the Optimum Q_max will provide maximum efficiency, and a Q_max close to the Maximum Q_max will yield smaller and possibly less expensive TECs. Reading down the Q_max column results in the selection of the following TECs:

For this example, let us assume maximum efficiency is desired. Thus, the 5.6 amp, 8.2 volt cooler is selected, because between these two potential TECs, its Qmax (30 watts) is closest to the optimum Qmax (36 watts).

Figure 2