A 20' wide screen that produces a quality image midday in a room with a large bank of windows would require industrial strength lumens to properly illuminate. Knowing the exact model of the current projector would tell us how many lumens they were previously satisfied with having. Then it would be a matter of understanding whether or not they would prefer the new projector to be somewhat brighter or roughly the same as the current model.
Another question would be the aspect ratio of the current screen, i.e. 4:3, 16:9, 16:10, etc., as it would make sense to get a projector with the same native aspect ratio as the screen. Of course the always important question is how much they have budgeted for the new projector. There are some pretty bright business projectors available at fairly reasonable prices as long as they have reasonable expectations for what they're willing to spend. There's no reason to consider theater-type projector models for this specialized bright room use as they are more optimized for optimum black levels than maximum lumens.
With video projection setups the devil is in the details. So if you really want to be helpful in choosing the best replacement projector it's important to have answers to questions like the ones above.