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It is quite easy to find pdf or books for properly design refrigeration piping. It is not that common though to find literature concerning heat pumps piping, especially when split (e.g.: reversible CU+AHU).
Anyone by any chance does have any such paper handy to share?
Thanks. I'll give them a look. Cheers.
edit: not quite what I was looking for. Suppose I bought a reversible condensing unit (not VRV) from manufacturer A and an AHU from manufacturer B. Neither of them has a dedicated piping construction manual.
ASHRAE falls short of this, as they only publish a refrigeration piping design handbook, but misses important info for heat pump operation.
Most manufacturers show a piping schematic in their tech/service manuals, is that the sort of thing you are looking for?
The pipework would/could fit from two different makers but the control side would be a different matter.
Not quite. I'm looking for a piping design handbook, that specifically addresses issues for reversible systems. I've got the ASHRAE refrigeration handbook 2009 and it really falls short on this.Quote:
Originally Posted by Brian_UK
The control side of it it's a different matter I'll be addressing at a later stage.
.
They don't exist generically.
In principle mass flow rates are applicable for AC, fridge,
heat pump or any other vapour compression refrigeration
system, but in practice individual manufacturers design
pipe runs differently.
What with ref nets, 2 pipe, 3 pipe, oil traps, no oil traps
and a thousand and one other things.
In heat pump / AC design all the different manufacturers
do use different pipe layouts and therefore there will not
be one definitive answer to all the designed systems there are.
They must all follow basic principles but variable refrigerant flows
do require complex control to ensure all the correct bits of refrigerant
should be and then there is the oil :) . So because all the manufacturers
use different systems, finding a one fits all is difficult.
Regards
Rob
.
I'm not interested in manufacturer's specific instructions. I'd like to combine the knowledge of refrigeration piping, which I have, with the obvious compromise required when in reversed heat pump mode.Quote:
Originally Posted by Rob White
Good question. That's what I'm looking for. Somewhere there should be information pertaining. Or is it all father-to-son by word-of-mouth?Quote:
Originally Posted by Rob White
mitsi and daikin only do cooling only dx systems for 3rd party ahu manufacturers, ive searched ahu manufacturers and most manufacurers use lphw coils or electric heater banks, air handlers have dx heatpump units within the ahu's but its built within the unit ,swimming pool heatpump manufacturers use dx but again integral units, not found a remote condenser for an ahu that's heatpump too.
http://www.novair.it/index.php?lang=enQuote:
Originally Posted by install monkey
http://www.clint.it/prodotti_catalog...&m2=25&lang=en
There you go, just to mention two, but there are others like Rhoss MHAE.
And please stop the morse thing. Move to another thread, please.
both links only lphw and chilled coils no mention of dx heatpump option with remote condenser, they do show rooftop style heatpumps but the pipework is done by the manufacturer.
No. You're wrong.Quote:
Originally Posted by install monkey
http://www.clint.it/prodotti_catalogo_prodotti_dettaglio.php?id_prodotto=33&nome=MHA/K%20182%F7604&id_cat=4&id_vers=2&id_comp=&id_scam=&id_vent=&id_ref=&id_sol=&m=02&m2=25&cerca=si&lang =en
I'm not discussing about remote condensers, please see the original post. I'm discussing about AHUs, suitable for being reversed (coil only installed) in connection with a remote reversible condensing unit.
This is a very common solution alternatively to heat pump rooftops for high capacities.
But again, should ever the pipework be done by the manufacturer, what are the criteria they would follow to design the refrigerant piping?
Or is it all father-to-son by word-of-mouth?
Let's see it under another POV: I am the manufacturer and need to write a piping design manual. Where do I start? Surely not from the ASHRAE handbook, which does not cover my case.
York/Johnson controls do these, i've installed a bunch of them.
Installation manuals give specs for pipe sizes and max runs. If reversible then non return valves/check valves installed etc. Is it this information you need?
alec
Maybe. Are there calculation criteria?Quote:
Originally Posted by al
NNN, I'm sure you know the basics (and far more) of calculating the lines for an AHU.
We installed several AHU's (and several PHE) to Mitsubishi for example. We use the same pipes as we should connect to their original indoor units. That's what Mitsubishi is recommending.
The coils in the AHU - but your know this for sure - must be constructed in such a way that the liquid always can flow downwards the coil when used as a condensor. (Do you remember the faulty Blue Box Coil coil we discussed once together?)
I should recommend proper speed in the lines (with max 1K temperature difference across the pipe) to ensure proper oil return.
I'm sure you can use the same rules as used with refrigeration but you have to use higher speed to counteract lines which aren't always installed in the field the proper way.
For VRV's other techniques are used to return the oil to the compressors.
Yes, Peter, but what amazes me is that nothing is told about this anywhere.
Let's make a real life example.
I've got a dx coil on a AHU, 10000m3/h, sized for all fresh air 35°C 50% on coil, something like 16°C 99% off coil, at an evap temp of 7°C.
Now I want this coil to be used as heating coil in winter: 45°C cond temp, 5°C 87% on coil, 29°C something off coil.
At 15-17°C on coil, high pressure alarm. I should then unload if I may, and recovery if the AHU has got one.
If that happens, then my piping should be sized with double riser or not whether the CU is over or under the AHU.
Secondly, the AHU has got temperature probes but only the CU has got pressure transducers. An issue arises about when the CU should unload, without it knowing the actual on coil temperature.
This is quite complicated without a proper coordination.
And note that the on coil condition is not the actual return air temperature!!
It really comes down to understanding the application.
You are indicating that you are running low loads (low refrig velocity), for long periods, then you size as you would any other refrigeration system, including double risers. I do not see this as a reverse cycle issue but a understanding issue. You may need to separate the heating and cooling cycle, and see what happens for a chosen pipe selection.
I am not sure I understand, you load/unload issue, you are either driving directly of a process variable or of a refrigeration variable.
Or are you controlling the air volume, to achieve fixed outlet air temp.
Not at all. I need to control the building temperature, which is much different from the off coil condition.Quote:
Originally Posted by mad fridgie
And I need to control evap and cond temperature depending on the on coil condition which may be different from the return air temperature. In fact AHU may have mixing sections and air-air recovery sections.
This is quite a riddle.
Amidst this, refrigerant velocity should be controlled.
If we take a step back from the detail.
We have a fixed air volume, (but difference in energy density)
In heating mode, would it be fair to say, that if the air entering the coil, is closer to set point, then the actual amount of energy required to keep the building warm is less, and that the air exiting the coil need not be as warm. So if this is the case it is quite simple to adjust the load profile to suit (with a deviation factor to find a comfort level)
If this system is not close control, then your oil return could easily be resolve with pulses of high load, and/or changes in refrigerant density.
Install a room thermostat which sends a PID signal 4-20mA (or 0-10V) to your controller.
This controller adjust the SH to increase coil temperature as setpoint is reached (opening or closing EEV)
Compressor maintains a stable TE by in- or decreasing compressor speed.
Due to the increased SH, Tdisch will rise, so an additional EEV adds refrigerant to the suction to maitain a stable Tdisch. HP is kept within working conditions with proportional fan control.
Oil return is insured by opening the EEV on indoor (even close to 0 SH where liquid floodback is prevented by a suction accumulator) and reducing speed of the fan to increase line velocity to flush the oil out of the lines. This is done after calculation how long the compressors ran on a reduced capacity (low speed in the lines)
That's how Fujitsu, M.E. and Daikin works with an external DX-coil.
Does this make sense NNN?
No. The on-coil temp is after the air-air recovery section. It's all-fresh air, therefore independent from the building temperature. The on-coil temp is proportional to building temp only at fixed ambient air temp.Quote:
Originally Posted by mad fridgie
If Fujitsu and Daikin do so, then it must make sense. I'll think about it. I'm not sure whether Fuji e Dai make all-fresh air handlers, though.Quote:
Originally Posted by Peter_1
Thanks.
They don't make those NNN. If you have a Heat recovery on the air, is the entering air then on outside conditions when entering the coil? Is most of the energy from the contaminated exhaust not transferred to the fresh air supply?Quote:
Originally Posted by NoNickName
Yes, until entering the recoverer the fresh air is at ambient conditions.Quote:
Originally Posted by Peter_1
Yes, at least 50% of the heat is exchanged. % is higher when ambient is colder (of course: greater dt between the two sides)Quote:
Originally Posted by Peter_1