Warehouse space heating

[Chemister]

I am currently working on an energy management project focused on an industrial warehouse (pulp). I am trying to understand how the warehouse is heated to estimate the energy used and suggest energy saving measures. From what I understand so far, glycol is heated either by a separate boiler (its operated only in winter) using natural gas or by steam from another boiler. The steam exits the boiler header and splits to serve multiple purposes: production processes, electricity generation, and heating glycol (desuperheating steam).

The hot glycol flows through pipes and splits off to unit heaters, where fans move air across the glycol coils to heat the surrounding air in the warehouse. Additionally, the glycol heats air in air handling units, which recirculate the air, and it also heats air from the makeup air unit.

For controlling warehouse temperature, they rely on an On/Off fan operation with the following control logic:

When the fan switch is set to "AUTO," the fan operates only if the warehouse temperature drops below the set point (7°C).
When the fan switch is set to "ON," the fan runs continuously, regardless of the temperature.

I asked people in the facility they told me they have no other controlling method.

For airflow, I asked whether the building has vents to exhaust air. I was told there are no dedicated vents, so the makeup air from the main air handler simply finds its way out of the building naturally. The warehouse walls are concrete, and the door heaters, mounted above the doors, provide adjustable air curtains with 90° nozzles pointing downward to prevent cold air inflow.

My concern: With no dedicated vents and the present control method won’t the continuous heat addition from glycol lead to a gradual temperature increase in the warehouse?

 

[waross]

Look at the heat loss through the walls and roof as a function of temperature difference.
Heat in equals heat out.
When you have solved that, consider heat loss in the air curtains and add that in.
Air curtain loss may be negligible or it may be considerable depending on how often the doors are opened.
And due diligence may suggest checking the temperature of product entering the warehouse.
If the product is above ambient temperature it may be relieving the unit heaters of part of the heating load.

 

[Snickster]

It is not clear what you are saying. So unit heaters are on-off controlled at 7C but glycol continuously circulates through them? Are they individually controlled or all controlled by one thermostat? So make up air unit is always on? Door curtain units are always on? Doors are kept open or closed? Need much more specifics. Why would building heat up uncontrolled?

 

[vint-j]

There are a few things to figure out here. Start with the heat loss through walls and roof—how much depends on insulation and the indoor-outdoor temperature difference. Check the air curtains too; frequent door openings could make heat loss through them significant. Incoming product temp matters as well—if it’s warmer than the room, it might reduce the load on the heaters. How are the unit heaters controlled—individually or together? Does glycol circulate constantly, even when heaters are off? Are the make-up air and door curtain units always running? And how often are doors left open? If the building heats up on its own, there might be unregulated heat sources or something misaligned in the system. Sorting out these details should help pinpoint where things can improve.