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Thread: Rack liquid level up and down
02-09-2013, 02:18 PM #14"The problem is the average person isnít tuned in to lifelong learning, or going to seminars and so forth. If the information is not on television, and itís not in the movies they watch, and itís not in the few books that they buy, they donít get it" - Jack Canfield
02-09-2013, 02:21 PM #15
....unless your reclaim coil is grossly oversized."The problem is the average person isnít tuned in to lifelong learning, or going to seminars and so forth. If the information is not on television, and itís not in the movies they watch, and itís not in the few books that they buy, they donít get it" - Jack Canfield
02-09-2013, 02:48 PM #16Regular Guest
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- Sep 2010
02-09-2013, 03:01 PM #17"The problem is the average person isnít tuned in to lifelong learning, or going to seminars and so forth. If the information is not on television, and itís not in the movies they watch, and itís not in the few books that they buy, they donít get it" - Jack Canfield
02-09-2013, 03:26 PM #18Regular Guest
- Join Date
- Sep 2010
02-09-2013, 04:50 PM #19
Apparently I'm having a brain fart here.........but isn't the reclaim coil supposed to be installed before the AC coil?
My thought is we'd want to heat up the return air before it hits the AC coil which would increase the return air temp on the AC system...and subsequently dehumidify the environment.
With having the reclaim coil positioned after the AC coil, doesn't that simply act as an extremely efficient rack condenser?
02-09-2013, 04:59 PM #20
02-09-2013, 05:37 PM #21
02-09-2013, 05:52 PM #22
Yep, the HR coil is supposed to be placed in the reheat position, immediately after the cooling coil...and before the main heat source.
For dehumidification, you're basically running the A/C get the moisture out and at the same time adding sensible heat with the HR to avoid overcooling the store. Markets are different animals for when it comes to dehumidification because there's a high latent load with a relatively low sensible load...even in the summer due to the mostly sensible cooling effect from the cases.
A 50,000 Sq Ft department store might have 120 tons of A/C whereas the same size supermarket might only need 80 tons. The problem is their latent loads are nearly the same, so lots of reheat is needed.
02-09-2013, 06:06 PM #23
Yeah, that's what I meant ......
02-09-2013, 06:32 PM #24
02-09-2013, 06:47 PM #25
Heat reclaim is always after DX cooling in just about every supermarket application I have seen. Not saying it can not be the other way. But what I have experience with is HR always after.
It is because its for Dehumid in a central HVAC system. When in Dehumid, we DX cool ( our only means to dehumidify) and if the DX cooling falls below AC setpoint, we reheat with HR up to cool setpoint so we don't over cool the space in dehumidification.
Guys often mistake reheat as something to do with dewpoint. Not so. Were just reheating so we don't over cool below cool setpoint on a dehumid call because we have to use the dx cooling to do the removal of moisture in the air.
The fact that your falling to 0% during HR, also tells me the Heat Reclaim is condensing liquid all by itself, as Mathew is saying.
What Matt (phaseloss) is saying is, a Series Heat Reclaim would only be big enough to desuperheat. And you may have proven this this. You forced reclaim, with Blower off. It did not condense. You did not swallow up all of your liquid in the receiver. You turn the blower on, and whammo, she drops.
When the blower is on and the fact it is condensing, Matt, and I agree, were speculating the Heat Reclaim was intentionally designed to be a parallel design, which is not all that uncommon but misunderstood. In a parallel design, you do not divert to air cooled condenser while in Heat Reclaim, but use HR as the condenser. It's sized to do all the work by itself.
When Not in HR for either heat or Dehumid, you use the air cooled condenser.
It's either or. It's in HR for either heat or dehumid aka >>> reheat. If either one of them guys is not being asked for, we are asking the normal condenser to do the work.
In series, it calls, it goes through the HR coil first, it desuperheats the discharge gas, and routes up to the aircooled condenser to get the rest of the work done, condensing and subcooling.
The other issue here we have to think out is the fact that in Hot Gas defrost, we falsely raise head pressure, (creating pressure difference from the discharge to the liquid manifold) to send superheated gas to the defrosting case, coming back as condensed liquid to liquid manifold as to feed the other circuits. This will cause the receiver to spike and trend upward during hot gas. It has to. Returning liquid is what will feed the other liquid hungry circuits, because this liquid coming back typically (use this word "typically" very loosely) will be a tad higher than receiver at this point while the liquid returning from what ever condenser is active, is being held up in the receiver.
I am here to learn as well. But below is how I have always seen this stuff and successful with setting up, with these truths:
So if the drop leg is common to the receiver (captain obvious is me) and it gets liquid either from the Heat Reclaim Condenser or from the Air Cooled condenser, if we in fact (we did not see these, but not sure yet ) if we are using low ambient valves to flood it would be on that drop leg, and getting liquid from the active condenser, which ever is active. This is where that guy would be.
Low ambient valves (flooded condenser) are to achieve some set minimum receiver pressure and only actuating when we fall below all other lines of defense to keep minimum head pressure from falling below some pre engineered, predetermined point (above my paygrade)?
Split is a line of defense for maintaining minimum head pressure in low ambient also but intentionally designed and it is an objective to reduce refrigerant charge.
You will require less overall refrigerant charge, since you always first split, and if so equipped with flooded condenser low ambient valving arrangement, your not using the extra liquid to flood a full condenser to maintain minimum receiver pressure.
So the low ambient valves would be our LAST line of defense to maintain minimum receiver pressure.
You split first, and only off the ambient value. And that is it. Nothing more. As our ambient drops, we need to downsize condenser capacity, or we go too big a condenser.
You Fan cycle only off the head pressure value.
These two settings are totally indenpendant of each other.
Your Hold back (flood condenser) is always last line of defense and on some set minimum receiver desired. likely the lowest liquid you want flowing to the TXV'x.
I think you guys understand why I keep saying flood condenser low ambient valve arrangement is to set minimum receiver. But maybe some guys who are with us here do not. So. When your holding back, there is always a receiver pressure regulator off discharge. It is set to the difference between discharge and receiver. If the receiver falls say 20psi below discharge, it's goon divert hot gas to the receiver. So, while actively holding back drop leg to reduce condenser effective surface area, our receiver may fall below that by 20 psi difference. So it's our goal to always set valves with the end game what is the lowest receiver pressure desired. Which is basically our lowest full column liquid pressure to the TXV."The only real security that a man can have in this world is a reserve of knowledge, experience and ability." Henry Ford
02-09-2013, 06:56 PM #26
I am wrong about hold back position. Damn it."The only real security that a man can have in this world is a reserve of knowledge, experience and ability." Henry Ford