are you assuming that a user will have your page open continuously for more than 3 minutes (which would probably be unlikely)? If so, you could use a meta refresh:
<META HTTP-EQUIV=Refresh CONTENT="180">
Otherwise, the data should refresh every time the user opens the page.
To let the users know how up to date / out of date the data is, you could put the date & time on the page, such as:
I am a loud man with a very large hat. This means I am in charge
<p>Page created at <% =Now() %>. <a href="#">Refresh</a></p>