Electric heaters for the Greenhouse

Question

Greenhouse/Company restaurant with heating
Because of the environmentally conscious design of "the Greenhouse" no gas is present and the heating must be as green as pos
Because of the restaurant function, the heaters should not make too much noise.
No possibility to hang the heaters on the construction of the building, so must be different.

4x Electric fan heater, 24/12kW working on 3x 400V three-phase current
4.9m high steel floor stand with heater on each side for even displacement of hot air
1x Programmable room thermostat for controlling the temperature for all 4 heaters from 1 point onwards
By using different speeds the noise level of the heaters can be reduced.