What are these copper pipes in ductwork?

Inspected an updated condo in a 1920 building in NJ. Concrete floors/ceilings, but where they ran some ductwork for the cooling system it is covered by finished ceiling. Popped my head up in an access panel and saw this in the ductwork. Anyone have any ideas what these u-shaped copper piping is entering/exiting the duct? At first I thought it might be a heating coil inside the duct, but the thermostats for the air handler / ducted system was cooling only. The heat was supplied by baseboard convectors. Both AC and heat was included with association fees (huge condensers on the roof for cooling, huge boiler in basement). AC and heat was controlled on the unit level. I can finish my report without knowing but I’m just really curious what it is.

That is a coil.

Yeah, that’s what I thought but it’s so odd that there are no controls for it on the thermostats and didn’t see a separate control for it. I reported it appeared to be a heating coil and I couldn’t find the controls, so to ask the owner about it and also have the HVAC tech servicing the unit (for another reason) inspect it. I also talked to the client about it explaining the same thing.

It is a heat sink, it transfers heat or cold to the incoming air to help warm or cool the air before it gets into the home to help with costs. There aren’t any controls for this as it just circulates liquid thru the coil when the system is running.

That’s an inline cooling coil and the controls would be up inside the rooftop unit and tied to whatever cooling thermostat in the apartment.

Thanks for the confirmation so far. It’s in the supply duct, downstream of the evaporator coil. If it is a cooling coil/heat sink with cold liquid running through, couldn’t condensation result inside the duct? I didn’t see a condensate management system below that coil. How do they handle that?

I would imagine there are modulating dampers that control the temperature of the air and temperature of the cooling coil all controlled by the roof top unit.
You might be best to recommend an HVAC technician to help you out here.

Thanks Marcel. That makes sense and wondered if that could be done, which you confirmed for me. I did report it as unknown/not inspected (it was 50 degrees her in NJ) and suggested an HVAC contractor look at it since they were already going to be there for another reason. All of this was for my own knowledge…I do a lot of business in urban areas so I’m always seeing new scenarios with large, HOA-owned systems and I want to be able to explain to an interested client how they are working. It’s all out of scope since it is owned by the HOA, but I want to be educated. Thanks again.

If it’s in the supply duct downstream of the evap coil, then what you’re looking at might be a reheat coil.

Right, except this ductwork was only used for the AC. There was no furnace or any type of heating system in the cabinet, just an air blower and evaporator coil. The digital thermostat only had a cool option, not one for heat. That’s why I had to ask the forum, because I’ve never seen this as part of a cooling system, only as part of a heating system.