make existing single zone system multi zone 1

[geordiejohn]

Hello All - my first post.

I'm looking at a large single zone mixing/recirc AHU with hot water coil and space for chilled water coil. This supplies a large open factory in Ireland. The factory is being converted into offices, several zones some small, some large.

My first thought is to relegate the AHU to fresh air supply only then use VRV/VRF for individual zone control, but I'm wondering if it can be done with VAV less expensively and install a chilled water coil etc onto the AHU...

Any ideas guys?

 

[Compositepro]

Termafusers may work but they are tricky to apply so that they don't cause other problems. They are diffusers with mechanical thermostats. The main thermostat, of course must be in the zone with the highest heating/cooling loads.

 

[geordiejohn]

Thanks Compositepro
I like the idea. I haven't seen them used here before. Trying to reuse the existing plant obviously cannot provide simultaneous heating and cooling in adjacent offices without another system...

 

[Compositepro]

One thing that may not be obvious to those unfamiliar with them is that the thermofusers have three thermostats. One to detect incoming air temperature to switch between heating and cooling mode, and one in each mode for temperature control .

 

[geordiejohn]

So say the system is in cooling mode supplying cool air to all rooms. An unoccupied perimeter room needs heating. The termofuser closes the damper reducing air into the room (say to 8 l/s per person). Then the heating requirement must be picked up by say perimeter heating with radiators. Then similtaneous heating and cooling. Hmm. But it would work.
Also presumably higher ceiling preferable for comfort. Do these work well in heating mode? what range do they have 100% air volume down to 30%

 

[SAK9]

Assuming you have CHW and HHW, a good option seems to be:

Use the existing AHU to serve either the internal or perimeter zone( depending on design air flow requirements).Provide VAV boxes with terminal reheat coils.

Provide a seperate AHU for the internal zone which will be doing cooling most of the time again with VAV boxes with no reheat.

If it is an air based system for heating,I would suggest ceiling height to be kept around the 2.8m mark.

 

[willard3]

Trying to heat with air from overhead is a losing proposition.....the higher the ceiling, the worse the problem.

 

[geordiejohn]

Thank you SAK and Willard.
The building is a big 2 storey open box which will be fitted out for call centre and cellular offices. There is an existing AHU which has space for a chilled water coil to be fitted.
Most of the year will be predominantly a cooling load with small perimeter heating load.
I've reached the conclusion the lowest cost adaptation is to use the AHU for the call centre and position the cellular offices around the perimeter of the building with perimeter radiators and local DX systems (VRF or VRV).
It would be possible to convert the AHU to VAV but the duct is not pressure tested, the fans are comparatively weak, the job is cost driven...
High ceilings (4m) for the large call centre are preferable with low ceilings for small perimeter offices (3m).