Really depends on your meaning of DR and the amount of equipment required. I have been managing a large number of Bank data centres for over 20 years and the only way to work out what is required is to calculate what IT equipment is required and design the requirements to this. Don’t forget to add in the heat losses for the building and the power requirements for the temperature rise. I normally ask what is the future expansion predicted and double it, as power and cooling is difficult to change. (& the IT guys never get it correct)
IF the DR is on the same site you may not need additional power & cooling as the existing design may have sufficient building segregation and system redundancy built in. If the site is different you need to treat it like a stand alone site and it will also need built in redundancy.
If you are only considering the power & cooling DR, you need to ensure you have sufficient fire and system isolation to allow you to run in DR and also perform maintenance. This is often a 2 time normal (2N) requirement. If my plant room burns out how long can I run in DR mode, how will it effect my business requirements, remember it may take up to 2 to 4 months to rebuild.