Open vs Closed- Loop System on Size of Dryer

[invent11]

To preserve piping and equipment in our mothballed plant, we intent to utilize desiccant dehumidifier to blow dry air in systems and maintain RH in range of 30-40%. Dryers will be installed indoor. I appreciate your insight on the followings:
1-What is governing formula for sizing the dryer?
2-What is ratio of dryer capacity in case of a closed loop vs open system (venting air)? How much larger dryer becomes for an open circuit as we have challenges to establish a closed loop drying.

 

[EnergyProfessional]

30-40% seems an awful low RH requirement, that you probably didn't achieve while it was running. Where did you get that requirement from?

Sizing of dehumidification obviously depends on the OA infiltration and with that the climate. and what temp is supposed to be in there? If you allow it to drift to 90°F in summer, 30% may be easy. but if you want 70°F, 30%RH are difficult.

 

[invent11]

Thanks HerKa but if we allow 90degF what is your response to my questions above.

 

[EnergyProfessional]

it really depends:
- what climate
- will any processes take place producing humidity
- what infiltration / ventilation
- any heating or cooling going on
- how critical is meeting the 30-40% Can it exceed for some days? thsi relates to the question why you need 30-40%?

for example,if this is an empty hall in Colorado, you don't need to do anything. If this is a Florida warehouse with some indoor water evaporation you need to do a lot. It all depends on the above...

 

[invent11]

Thanks Herrka- my Q is about drying internal parts of piping & equipment bring the environment to the range of 30-40% RH humidity as a part of our preservation plan to prevent corrosion. As we keep the internal pressure slightly above atm, we do not expect any source of humidity after initial dry up period. Dryers are installed indoors. Q is what formula i should use to calc. the needed flow rate for dryer. What would be difference btwn close loop and an open system. By open system i mean venting air to atm (again indoors) at or close to the end of piping (i may need to vent in few spots on circuit). The reason we are considering venting is due to difficulty we are facing to route ducting back to dryers.

 

[invent11]

Herrka others any thoughts/answer to my questions.

 

[ChasBean1]

Scrap your plan. Get a bottle of nitrogen or argon gas and a regulator, find a tie-in point and pressurize the system to 0.5-5 psig. Bleed off remote points and then close everything, leaving the system on a N2 or Ar "blanket" for your shutdown period. The system will be near 0% RH and will have no oxygen, which is the key to preventing corrosion.

 

[invent11]

Unfortunately due other considerations we cannot use N2

 

[ChasBean1]

Why not nitrogen? Try argon. If not, try a bottle of compressed air. They come with 0% RH. If you're hell-bent on maintaining 30-40% RH (any sense in this escapes me) then there are ways by having blow-through with a heating coil, where its modulation would work inversely to the leaving humidity... As leaving humidity approaches 40%, reheat fully opens; as humidity approaches 30%, reheat fully closes.

 

[invent11]

The intake air will be about 100 deg F and 70-80% RH in summer and equipment design temp does not allow high temp. Therefore i think our best bet is to go for dehumidifier (descant dryer).