Simply put, your system isn't 24kbtu IF your restraint is ideal reservoir temps.
PERHAPS, send 55 degree water through the air exchanger to warm the water prior to it hitting the reservoir exchanger?
Even more tuned, a bypass solenoid valve / cooling thermostat with remote probe arrangement to bypass the reservoir when it's cool enough.
Last first; Hydro Innovations sells just such a solenoid controlled water temperature management kit, so I've looked carefully at the application.
I'm not sure I fully agree with your suggestion that I'm not running at 24k BTu; the chiller runs most of the time as it should, and none of the rooms goes completely off the reservation. AT THE AIR HANDLERS in the rooms themselves, on the other hand, I definitely agree with your assessment that these aren't moving the necessary BTu.
Here's why I'm so reluctant to reduce chiller circuit temperature; without a solenoid, water temps in the cooling circuit and the RDWC trend towards one another at a steady rate of one degree f every few hours. For 125 gallon reservoirs, I find that reasonable, since they never warm up by more than a degree or two during normal daytime operation. At night they cool again, etc, etc.
During the summer, daytime heat loads rise dramatically- at the very same time AC compressors have the hardest time shedding heat! So why don't MY afternoon temps skyrocket, especially conducting my system runs with little or no overhead capacity?
What I discovered was that the chilling system actually uses the thermal mass in my RDWC to maintain room temperatures during the hot part of the day; those cold coils warm up past the temperature of the RDWC- and start drawing cold from the 'bank' all afternoon, until temperatures outside fall enough for the chiller to catch up again.
At two Tons, I think my chiller is being assisted during the day so that the system as a whole temporarily operates beyond the chiller's rated cooling capacity. This is an advantage I'd lose with solenoid controlled RDWC chilling- and there's no way I'm replacing several hundred gallons of thermal mass easily.
It's this phenomena that I'd like to preserve if at all possible- because it's effective even with a large overcapacity in HVAC, in cases where some cooling capacity might be offline, or just not needing to buy as much capacity as might otherwise be needed.
This is why I'm investigating the use of larger condenser cores at the moment. I'm even considering a dual pass approach, shoving warm room air through a squirrelcage blower and through one half of a big core- and then right back through the other half. The idea is to wring as much moisture out of the air as possible by presenting the core twice.
Finally, the higher the temperature in the cooling circuit, the less incidental heat it will gain through lines and reservoir walls. This translates into significant energy savings over time, as well as reduced installation costs due to a smaller temperature delta.
I've given you all I got. 
