hydronic unit heaters versus steam cast iron radiators

Russ Hugenschmidt_3

I am not an engineer and am looking for some assistance in reviewing the benefits from a cost and operation view for hydronic unit heaters versus cast iron steam radiators in an industrial application.

We currently have a plant in China that is using cast iron radiators to heat the plant. All steam radiators are in use throughout the plant as there is only one main boiler. We are looking at using modular boilers to heat zones. In addition, we are looking at changing out the steam radiators for hydronic unit heaters that are hanging from the ceiling.

What advantages and disadvantages would the unit heaters have over the cast iron radiators? What energy savings would we hope to get switching from a single boiler to modular boilers? What energy savings would we hope to get switching from cast iron radiators to unit heaters with modular boilers?

Brad White_9

Russ-

Here are some general thoughts:

1. Heating Medium:
You mention steam for the radiators and hydronic, specifically, as hot water, correct? Is steam an option for either or both? It may affect your choices. Is the steam available as a by-product of another process such as generators, turbines? In other words available all the time versus made just for heating? If you are creating steam or hot water just for space heating, hot water has a slight edge on efficiency. Steam moves without a pump (but the condensate has to be pumped back). Water can vary in temperature but when using unit heaters you may be limited in how far back you can set the temperature.

2. Cast iron is hard to beat for steady output whether steam or hot water. It is easy to clean, durable and comfortable with no drafts. Radiant effect heats without air currents. Even if the space is heavily ventilated, the heating will be of benefit to the people. And they have over a billion of them

3. Unit heaters can be fussy to locate, especially if near overhead gantries, pneumatic lines, cable trays and power drops. Can be drafty and require electricity to run. They can help de-stratify a high-ceiling space but this may not always be desireable especially if the high parts of the bays are filled with welding fumes, smoke, excess heat or process mists.

4. If the conditions in the factory are dusty or linty, it can clog the fins of unit heaters. Maintenance item but a loss of capacity is about guaranteed. Motors are exposed to what kind of environment?

5. Recovery: Cast iron may not recover well if near a door, so you could install a unit heater or heaters near a door to give a boost to recover temperature after a door opening cycle. Unit heaters cover particularly well if properly sized. But they are low-mass so should not be combined on the same zone as cast iron. They want to have priority.

6. Given a choice, I would stick with cast iron and go to hot water if that is possible. You would have to add more units to heat than if with steam (output is less by at least a third so you would add 50% to your radiation at least). But the comfort benefits are apparent and durable compared to electrically-driven heaters.

My $0.02,

Brad

clammy

radiant panels

If your going to use hot water instead of steam take a look at radiant vallance systems ,no electric so no fans cuts down on air movement and can be use not only to heat the building but you can put the heaters above where most of the work is taking place as for which is better either steam beats hot water at btu output on most heating devices (radators,fan coils )and the big plus is with steam is you don't stand as much damage from a freze as you do with hot water ,each has it's up and down points .It also depends how much are you willing to invest in a manafactouring plant in china .Sorry but when i got to the china part and manafacturing i kinda lost my interest peace and good luck clammy in the usa

Mike T., Swampeast MO

Is the steam used for other processes in the factory?

If so it seems odd (and inefficient) to not use the steam (or the condensate) for space heating.

If not cast iron rads are wonderful sources of comfortable radiant heat. Run the numbers to see if they'll provide sufficent energy using hot water instead of steam.

Don't forget to add in the heat provided by equipment, lighting and people! It's probably running 24-7-365... Don't forget to subtract out the heat lost via ventilation (if any).