1-805-484-2992
Quotes - Engineering - SalesUSP Purified Water, held at room temperature
Two duties, one exchanger
Purified Water meets the same conductivity and TOC limits as WFI with no endotoxin limit, and most plants hold it at ambient because a cold loop costs a fraction of a hot one to run. The price is that nothing in the loop kills anything, so the system is sanitized on a schedule: hot water at 80 C for one to two hours, or ozone destroyed by UV ahead of the use points. The loop exchanger is a trim cooler all week and a heater on sanitization day.
Sizing for trim duty and then asking the exchanger to take the loop to 80 C in the time the SOP allows is where PW systems go wrong.
Trim cooling, sanitization heating and ozone
The trim cooler that runs all week
A 100 gpm PW loop with a 10 hp pump puts about 25,000 Btu/h into the water from the pump alone, plus whatever the room and the tank pick up. Left alone the loop drifts to 30 to 35 C, which is the temperature at which biofilm grows fastest and the reason ambient loops are held at 20 to 25 C. The trim cooler removes that heat on chilled water with a small approach, and it is a small exchanger: 30,000 to 100,000 Btu/h on most systems. It runs continuously, so its double tubesheet gap is inspected on the same walkdown as the WFI units. A double-wall plate exchanger fits this duty well where the loop is never steamed, because the plate pack has almost no holdup and opens for inspection.
The sanitization heater that runs one day a month
Hot water sanitization takes the entire loop, tank included, from ambient to 80 C, holds it until the return RTD has logged 80 C for the SOP time, and cools it back. On a 5,000 gallon system heated in two hours that is roughly 1.1 million Btu/h at the start of the ramp, thirty times the trim duty. The heater is a double tubesheet unit on plant steam, sized on tank plus loop volume plus the tank wall, with a modulating steam valve on outlet temperature and a high limit at 85 C.
Cooling back down matters as much. A loop left to cool naturally sits at 40 to 60 C for hours, the range that grows organisms, so the cooler is sized for the cool-down too. HeatX usually quotes one tube side with a steam shell and a chilled-water shell in series, or a single shell on a hot water and chilled water header with a three-way valve. Cleaning and sanitizing the loop itself is covered on our purified water loop CIP page.
What ozone does to the exchanger
Ozone at 0.02 to 0.2 ppm in the loop is a superb sanitant and a poor neighbor to elastomers. Nitrile clamp gaskets crumble in weeks, EPDM in months. The water path in an ozonated loop has 316L, PTFE, and ozone-grade fluoroelastomer, and nothing else. The exchanger itself is unaffected; ozone attacks the gaskets, the diaphragm valves and the pump seals long before it marks the stainless. The UV destruct unit ahead of the use points is where the ozone leaves the water; the exchanger sits upstream of it in the ozonated section of the loop and is specified accordingly. Ozone loops still need a trim cooler, and many keep a hot water sanitization heater for an annual deep sanitization.
The common mistake
Sizing for trim and hoping for sanitization. A trim cooler rated for 50,000 Btu/h cannot take the loop to 80 C in any time the SOP accepts, so the site sanitizes on the tank heater alone, the far end of the loop never reaches 80 C, the return RTD logs 74 C after three hours, and the deviation report writes itself. Size the heater on the ramp, the cooler on the cool-down, and the trim duty comes free.
Give HeatX the loop and tank volume, ramp time and steam pressure, and both duties are sized in one pass. Call and talk it through with an engineer: 1-805-484-2992
Purified water loop process conditions
A water loop exchanger is sized on a handful of conditions, and the rows list them, including the ozone and sanitization limits. Compare them with your loop and send your return temperature and flow with the quote request.
| Condition | Detail |
| Product | USP Purified Water, ambient loop, 500 to 20,000 gallons |
| Flow range | 20 to 300 gpm, above 3 ft/s return velocity |
| Temperatures in / out | Trim 27 to 30 C in, 20 to 25 C out; sanitization 20 to 80 C, then 80 to 25 C |
| Hold | 80 C for 60 to 120 minutes at every point, logged by the return RTD |
| Utility | Chilled water 7 C for trim; plant steam 30 to 60 psig or 90 C water for sanitization |
| Approach | 3 to 5 C on the trim cooler; 8 to 12 C on the sanitization heater |
| Construction | Double tubesheet shell-and-tube, or double-wall gasketed plate for trim-only loops |
| Finish / class | 316L, 20 to 25 Ra mechanically polished, electropolish optional; ASME BPE SF1 to SF3 |
| Ozone | 316L only, no nitrile or EPDM in the water path; PTFE or ozone-grade clamp gaskets |
| CIP / SIP | Sanitized with the loop; drains dry between cycles |
Common FAQs
Against plant steam or tower water, yes by most site standards; on a chilled-water trim cooler some sites accept double-wall plates.
Most SOPs call for 60 minutes with every point at or above 80 C, verified at the return RTD. The ramp ahead of the hold is what sizes the heater.
Yes, on a hot water and chilled water header with a three-way valve, or as two shells in series.
Less than WFI. 20 to 25 Ra mechanically polished 316L is typical, with electropolishing where the site standard or ozone service asks for it.
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