Hi, how much algae culture do you need to produce? few mL? L? Even if you have no incubator, do you grow your algae in a lab at NTU. You could use ice to make it work depending of the volume needed. I am working nearby at DHI. PM if you want we could discuss more about that directly as I am at Cleantech Park. 

The incubator would be more precise but if you don´t have one, you can use ice cubes.

For how long and for waht volume of culture? That will be important for you to decide and design what is the most efficient, reliable and cost-effective system.

Thanks for your answers. Truly appreciate the helpful responses! For now I have two 20mL cultures and I put them under 12hr light:12hr dark cycle. I tried placing ice cubes around the culture flasks in a water bath, but I found that I constantly need to replace them as they melt too fast, even if they are in a half-closed styrofoam container. I then used gel packs, which lasted longer, but ultimately I may need an incubator if I have more cultures coming up.

Do you have access to cold water? If so you could set up a water bath; flowing at the needed temperature.

You should design a circulation system to have a constant temperature.If there is such a system available good to use it