Hydronic vs Steam
When it comes to design the building heat of a facility like an hospital or a big campus, most of engineers will design a primary-secondary loop through the buildings and mechanical rooms. The question is what to use as a primary; hydronic or Steam Water Heater?
If we assume that we need a 35 MMBTU primary heating system, with a hydronic loop you will probably have a design on high temperature (HTHW) with a differential temperature around 75F in order to reduce the flow that have an impact on the size of the circulation pump.
On steam at 125 psig, you won’t need any primary pump for circulation. And the pipe for feeding will be, approximately, the same pipe size but the condensate return will be much smaller.
There is 2 ways to design a Steam Water Heater network. First you can design the good old way, where you will require low pressure steam. The boiler will work at high pressure, to have smaller pipe to feed the buildings and mechanical room and than you will add pressure reducing valve stations, steam safety relief valves and condensate return pumps with vents to the roof and vacuum breakers that add constantly air and oxygen in the condensate piping creating rapid corrosion, which requires the need of amines.
Vertical Flooded Steam Heat Exchangers
The Second way; use vertical flooded steam heat exchangers which allow the use of high pressure steam through the heat exchanger. This technology, not only don’t requires steam pressure reducing valve stations but also it doesn’t need steam safety relief valves, it doesn’t need condensate pump stations and don’t even need vacuum breakers in operation. Way much simpler.
There is more to it… When you use vertical flooded steam heat exchangers, you have a 100% close loop. Which means, no need of a deaerator, no outside vents, no make up water so less water treatment and very low surface blowdowns on the steam boilers. Plus, if you have a minimum average load of 8 MMBTU, you can consider adding a saturated steam turbine directly connected to your main electric panel and generate a minimum of 100 kw, not bad is in it? In the south-east building heat is require all year to reheat the cool down air to dehumidify, in the north you might consider using absorption chillers in order to have steam demand to be able to generate electric power all year long.
What about the boilers?
Let’s discuss boilers. We can argue for a all week what is better between steam boilers vs hydronic boilers. Most of operators will tell you that a steam boiler is a way more robust construction than most of hydronic boilers and if your water treatment is well maintained, your boilers will last for ever. But they will also tell you that hydronic boilers are more efficient, combustion wise and system wise, because of the cold temperature return to the boiler and with hydronic there is no blowdowns and no deaerator which blow steam continually outside plus you don’t need all the other vents on secondary condensate pump stations. Again, a vertical flooded instantaneous steam water heater heat exchanger system address all those. Plus, if you bring colder condensate (feedwater) to a condensing stack economizer before entering the steam boilers, you will increase the total steam boiler efficiency.
Lastly, probably the most important point, when you have a steam leak, it’s never an emergency. You can continue running Steam Water Heater while waiting for the next shut down. On a hydronic primary loop of let’s say 1000 usgpm at 100 psig, the day that you will have a leak… good luck!!! You better act fast and you will probably need to shut down the primary loop system.
For those of you that still believe that a hydronic primary loop is still more efficient than a steam primary loop with vertical flooded steam heat exchangers, you should also look at the emergency maintenance care for the customers. The difference in the overall efficiency is not that great compare a maintenance peace of mind.