HELP choosing the right Arduino board? (Physics project)

This is my first time working with an Arduino board, i have limited programming experience.
Basically I'm writing a Physics Extended Essay for IB, the Research Question is: To what extent can a single solar panel maintain the temperature of an outdoor Jacuzzi in the spring? The solar panel is connected to a storage tank. I'm just collecting data for the heat gain of the solar panel and the heat loss of the Jacuzzi, and seeing whether the heat gain is greater or less than the heat loss in the Jacuzzi. I'll be collecting the heat gain/loss data during the day, at night the temperature will be reset for data collection the next day, and I'll take the average heat gain/loss over the 3 months.

So I need the Storage tank to reset at a temperature every night (ex: 20 c) for data collection the next day (the Jacuzzi can easily be reheated). The best way to do this is to keep the pump (what is circulating the heat-transferring liquid between the storage tank and the panel) running in the night, this way the solar panel will lose heat (the pumps stop during the night on a normal solar panel). I'm planning to have the board connected to a g-type thermal couple to collect and read temperature data in the storage tank and supplying electricity to the pump. The storage tank will be gaining heat in the day (from the solar panel) but losing heat at night. When the temperature hits 20c, the Arduino board stops the pump so (I hope it's insulated enough) it keeps that temperature. The pump is restarted towards 7am the next morning when the sun comes up for a new day of data collection.

At least that's what I hope I will be able to do. So I'm asking for help choosing the right Arduino board for the job and maybe hints/help for the rest of the project?
Feel free to ask questions if I wasn't clear enough or explain something I didn't get.
Thanks

What role do you expect the Arduino to play?

Controlling the pump?

Recording the temperature? To what media? (What post-processing will you be doing?)

Tracking time?

Will you be working with an actual jacuzzi? Will the owner be understanding if the pump is destroyed by a wiring mistake or bug in your program?

Simax:
To what extent can a single solar panel maintain the temperature of an outdoor Jacuzzi in the spring?

It depends on the weather forecast. 8)

Hi,
Any of the typical Arduino UNO or Duemilanove boards would be fine; you don't seem to need a lot of Input or Output pins.

Will/can the Arduino be connected to a PC to collect or archive data? Would be good to be able to make graphs with Excel etc.. maybe. I think an IB essay will be expected to handle data well and show results clearly.

I'm happy to see someone doing an IB Extended essay on a real physical problem! Let us know if we can help with questions. My wife was the IB Essay coordinator in Saudi Arabia a couple of years ago and almost every one was paper-in and paper-out. Us Engineers think that's BORING... Where are you located?

Take a look at relays and power on the http://ArduinoInfo.Info WIKI here: http://arduino-info.wikispaces.com/ArduinoPower

Look at temperature sensors etc here (I don't think you need thermocouple type): http://arduino-info.wikispaces.com/Brick-Temperature-DS18B20

Let us know how it's going...

I think the UNO is a good board to begin with, when you are satisfied with the project you can remove the chip from it's socket and solder it on to a circuit board.

Codling Badly: Yes I expect the Arduino to control the pump, but the pump will be circulating the fluid at constant speed; so I'll only need the Arduino to shut it off when the temperature reaches a certain degree.
I'll be recording the temperature with mini-log temperature recorders placed in the Storage tank, Jacuzzi and nearby outside. I'll be using excel to display my results (if that's what you mean by post-processing)
I don't understand what your asking with "Tracking time"
Yes I'll be working with an actual jacuzzi, the owner is my dad :/. And the pump will be circulating the fluid between the Solar panel and the Storage tank. The jacuzzi is separate and is currently heated by electricity (I'll only be measuring the heat loss and it can easily be reheated for the next day ) .The pump and the storage tank are items my dad bought from the company he was working for (which was closing) 20 years ago for a good price; he hoped they would be useful someday, well, today's the day!

Modeller: yes I know temperature and amount of sunlight are variables, I'm collecting data for the temp outside and at the end I'll contact enviroment Canada for the specific amount of sunlight those months to add in my essay.

terryking228: I'll be using minilogs to record the temperature, I can put the data on my pc to organize it in excel. Thanks for the links, if I have any future questions/concerns, I'll be sure to contact you.

arduinohabib: thanks, I guess I'll go with the UNO.

Simax:
Yes I expect the Arduino to control the pump...

One digital output.

I'll be recording the temperature with mini-log temperature recorders...

With a what? You don't want the Arduino recording the data?

I'll be using excel to display my results (if that's what you mean by post-processing)

Yes.

I don't understand what your asking with "Tracking time"

Time according to a wall clock. You mention "7am" in your original post. Do you expect the Arduino to determine when 7:00 AM arrives?

terryking228 ask an important question you skipped...
Will/can the Arduino be connected to a PC to collect or archive data?