Crack houses used to generate zero heat, but this feature was removed (or just nerfed? not sure) for it was too powerful.
My personal favorite are the factories (the two regular ones, not the garment makers). They don't have security guards, only nonunion workers and the occasional corporate manager. The nonunion workers are armed with chains only and pose no immediate threat, although you should bail out before you get a proper beating.
On the other hand, sometimes you need (or want) a decently trained squad without any unnecessary heat (defending a safehouse which houses legal operations like the Guardian is a good example). In this case, you may either use one of your already trained Liberals, have him/her community service the heat off (may take a while) and train some clean recruits, or alternatively kidnap & convert a soldier or an agent and use them as the trainer (much quicker). If you picked recruits with suitable abilities the squad should be ready for action without juice pumping first. If you need/want to juice them up, you'd best have each of them either grind stealthy juice gains until 200 juice or just have them hack (trains computer skill quickly as a bonus, and typically large heat kicks in way after reaching the 200 juice cap).
And a last note - violence in LCS is not good if you're alone. Even high juice people are only human - they can die from a single bullet in the brain. Bring a whole squad and prepare to replace fallen members if needed.