Here is link to a well written article about one pipe portable air conditioners
http://homeenergypros.lbl.gov/profiles/blogs/warnings-about-portable-air-conditioners
I do not understand the negative pressure on the two pipe system. A two pipe or duct system should be pulling in outside though one pipe across the condenser and back outside through the other duct. The only air leaving the space should be the air brought in form outside and no space air. But I have never seen a two duct system for a home. The two pipe units have been in the 3 to h ton sizes.
It’s a machine voice.
Nothing wrong with it with it with it with it with it with it
Response to Snnipe 70E re 2 pipe portable air conditioners
Since my previous post I have been in contact with Danby who presently market several models with 2 pipes. I also checked the input air flow rate of my 2 pipe unit, and it is only a small percentage of the output air flow rate (even with the input air filter removed). This is the reason a sealed room has a negative air pressure, and also the reason there is a considerable draft under the room door when shut Danby were unable to answer the simple question as to how air is routed between the room, input and exhaust pipes to pass through the condenser and evaporator. Due to the advertising for the 2 pipe units promoting the addition of fresh air into the room, it is most likely the input air is mixed with the room input air to pass through the evaporator, and all the air passing through the condenser is drawn from the room only. The condenser input and output would be the same as in the one pipe unit. This explains why the one or two pipe units are very inefficient, and why both types create a large negative air pressure in the room. The only real difference appears that the 2 pipe unit draws some air from the outside and most from the outside through the rest of the building, whereas the one pipe unit draws all it’s air from the outside through the rest of the building.
That sounds like a really bad design.
All the two pipe systems I have worked with the two air flows are completely separate. But the ones I have use are on the range of 3 to 5 tons.
Very nice presentation, but the 2 pipe units do not direct air from the input and output hoses (pipes) on a 1:1 ratio through the condenser as indicated in this video. They use a low flow of air from the input hose to mix with the room air input to pass through the evaporator to cool the room. They use a high flow of air input from the room to pass through the condenser and output hose. The vacuum in the room is created because the input hose has a low flow and the output hose has a high flow. I have a Kenmore unit probably manufactured by Danby a few years ago that clearly works this way.
The present Danby 2 pipe units are manufactured in the range of 11000 to 14000 BTU. Danby repeatedly are unable to answer cfm rates for the input and output hoses, and unable to describe the method for air movement through the condenser and evaporator with respect to the room and 2 hoses. Our building is in a dusty area, and we cannot use air from other rooms to make up for the negative pressure in the one room that is being cooled. We will have to provide an additional air intake to the room that is filtered from the outside. In doing this it probably won’t matter whether we use a one or two pipe unit.
All, I came across this thread while looking for a portable air-conditioner. There is so much incorrect information in it I decided to post. I am am engineer, with a degree in mechanical engineering and a degree in electrical engineering. I am going to attempt to overly simplify the information in attempt to clear up the information.
If you want the answer go to the bottom. The wall of text just explains it.
1st, An air conditioner is nothing more then a heat pump. It pumps heat from 1 location to another. Heat pumps require power (usually electricity) to function because they are doing the opposite of what nature wants, example is taking heat from a colder room (70deg) and pumping it outside to a 100deg outside. It can also run the other way, taking heat from a cold freezing outside and pump it into a warm 70deg room. Air conditioners obviously do the former.
Air conditioners generally have 3 parts, an evaporator that takes liquid coolant (such as Freon) and turns it to gas, a condenser that takes the gas coolant (such as Freon) and turns it to liquid, and a circulation pump.
So how does it work?
A pump circulates the same coolant around in circles hopefully indefinitely. Indeed most units need little to no new coolant after 10 years. My changing the pipe diameters (overly simplified but correct) the coolant is forced to change states. As it changes states it needs additional energy (heat) or has to get rid of energy(heat) to complete the phase change.
So every air conditioner has a HOT heat exchanger and a cold heat exchanger.
In the case of the units in question, portable air conditioners, the unit uses a fan to take air from the room blow it across the cold heat exchanger and then back into the room. All of them do this so there is no question here…
So is 1 pipe or 2 more efficent…
In the case of 2 pipes, the air conditioner sucks in air from outside blows it across the HOT heat exchanger and then blows out even hotter air.
In the case of the 1 pipe design, the heat exchanger sucks in air from the room, blows it across the hot heat exchanger, then blows out hotter air.
In either case, the amount of energy blown out is calculated by the mass of the air moved, and the change in temperature. Since the 1 pipe design has a higher change in temperature (70F starting instead of 100F) it blows out more heat.
The story is not done yet… if you constantly blew air out of your room without air coming back in then you would eventually have no air in your room and die. To maintain pressure, any air you blow out of the house has to be replaced by new air coming into the house. That new air is most likely at the same temperature as outside.
Now you blew out 70F air, to have to suck in 100F air. Thats bad…
Answer
So in short/general, a 1 hose air conditioner is less efficient then a 2 hose system because you are blowing cold air out of the house. Since the system is less then 100% efficient, it takes more energy to cool the new air then you gained by heating the cold air that you blew out.
Covering the part that people will think I ignored
Unfortunately, the answer still isn’t that simple. Fan head pressure comes into play, but shouldn’t change the answer. Air blown in a duct takes more energy to move then air that is free in a room. So having 2 ducts makes it harder to blow air across the hot heat exchanger then sucking air in from the room. You also have extra cost associated with the extra ductwork.
The additional fan energy should not tip the scales of efficiency but do tip the scales on price. As a result smaller units which use less energy (making it harder to recover costs to be more efficient) tend to only have 1 hose instead of 2.
The proceeding document was an apples to apples comparison. It is technically possible to make a 1 hose unit that has a extremely high efficiency heat exchange system, and thus more efficient than a 2 hose system with crappy parts.
I quote your statement "In the case of 2 pipes, the air conditioner sucks in air from outside blows it across the HOT heat exchanger and then blows out even hotter air. "This, is a reasonable assumption for a 2 pipe portable air conditioner, making it work like a wall or window unit. THIS IS NOT HOW 2 MANUFACTURERS PORTABLE AIR CONDITIONERS WORK. I have a Danby 2 pipe unit and I have seen a Haier 2 pipe unit operating at a store. In both cases, the flow of air through the input pipe is very low, and just enough to meet the manufacturers advertising that fresh air was being added to the room. The flow of air through the output pipe is high. The result is the room develops a negative air pressure compared to the rest of the building. Both 2 pipe and 1 pipe units create an almost equal negative air pressure in the room. They both cause hot unfiltered air to enter the building from window frames, door frames, fireplaces, ventilation fans, and any other leakage places. As I am writing this I am experiencing a strong smoke smell in the living room from a carousel fireplace that has no damper. The portable AC is in the bedroom. I will plastic bag the chimney and open a window a crack to fix the problem. BECAUSE THE CONDENSER GETS ITS AIR FROM THE ROOM, NOT THE OUTDOORS FOR ALL PORTBLE AC UNITS I HAVE SEEN, THE EFFICIECY IS MUCH LOWER THAN A WALL OR WINDOW UNIT. If you find a 2 pipe unit that works the way you suggest please post. I also am a P.Eng having worked in commercial AC and process control with a major manufacturer. However, a degree does not mean I have all the answers. Danby customer service could not provide me with the cfm for the input and output pipes of their 2 pipe units, or the source of the air for the condenser. I could not find a phone number for customer service for Haier where a live person answered,
“I’ll take 100 air conditioners for 200 hoses, Alex”
You seem to be the only poster here that has trouble with this. From here http://www.achooallergy.com/haier-cpn14xc9-portable-air-conditioner.asp I see:
And from here http://www.sylvane.com/dual-hose-portable-ac.html I get:
I have seen the Haier 2 pipe model HPF14XCM made for sale in Canada. The store was Future Shop. The input and output cfm are not the same. The PAC draws room air to remove the heat from the condenser and motor, with most of the heat coming from the condenser. The description in your post of how the 2 pipe unit works is incorrect for the unit I have seen. Have you checked the air cfm input and output on the Haier unit you indicated in your link. I will be interested in your response after you actually do a check of the unit, and not rely on the information sheets published by the manufacturers and the reviewers. A University or College degree is not required to understand this topic.
It seems this thread fails to make the distinction between the electrical efficiency of the portable air conditioner and the efficiency (rate) at which it cools a space. It’s also worth mentioning that the rate the space is cooled is not constant; it’s a compounding variable influenced by the total capacity of the mechanical compressor (pressure and flow rate), the boiling point of the refrigerant and the size of the condenser.
For the sake of argument, assume you have a “perfect” PAC in every way like a split system or room AC. When first started, it removes heat from the room at a fairly consistent rate. This rate begins to slow as the room temperature falls because the refrigerant condenses and boils at a specific temperature and pressure. The compressor’s capacity and (assumed) outdoor air temperature are constant; thus, it’s reasonable that the evaporator can only become so cold in given conditions.
A single-hose system first started on a hot day appears to cool its space far more slowly than the above dual-hose unit because a large amount of conditioned air is exhausted. However, the cooling accelerates (assuming the machine is properly sized) as the temperature drops because the capacity of the condenser does not fall as rapidly. But there is an additional variable in this scenario. The heat load produced by the pressure imbalance rapidly begins to negate any further temperature drop, far more quickly than the properties of the refrigerant itself. The single-hose system has a smaller envelope in which it is most efficient at cooling a space, but the overall efficiency in this region is greater. In practice, these systems are superior because both the compressor and exhaust fan can be of less capacity. A slower rotating fan for its diameter and lower compressor head pressure mean less drag, requiring exponentially less power to overcome. If you look at the average SEER for single-hose PACs, the numbers are higher.
I think there is an unspoken assumption about heat load and how space is cooled. If you only want to spot-cool one room in a large house with the sun beating down on it through ten-foot bay windows, the negative pressure does add to the heat load, but it is VERY, VERY MINIMAL. You’d gain the most from a single-hose PAC because it consumes less energy. A dual-hose PAC is better for cooling big areas where the additional heat load created by the negative pressure is (not completely, but largely) relative to volume.
If you’re evaluating a single-hose air conditioner, you need to look at:
a) Exhaust CFM
b) Size of room; the parasitic heat load is a function of this and the exhaust CFM
c) BTU for the heat load of the room excluding what is caused by negative pressure
In that order. It’s probably best for spot-cooling your bed or the dining room table.
If you’re evaluating a dual-hose air conditioner, you need to look at:
a) BTU for the heat load of the room
b) Dual-hose units can be made more effective by preventing exhaust air from recirculating back into the intake. This happens if you don’t remove your window screen and the hoses aren’t flush with it. A condenser’s efficiency is completely destroyed by recirculation because it heats a LARGE VOLUME of air only a few degrees above ambient. It’s limited by vapor pressure of refrigerant and the head pressure the compressor can sustain.
c) The condenser fan is only slightly larger than the evaporator fan, but I assure you it moves at least twice the volume of air and creates a pressure drop in the room given the outdoor air it receives. If you have a cheapo unit you don’t mind modifying, epoxy some duct wrap insulation in the plastic case halves to better seal the internal gaps and keep condenser air where it belongs. Best to glue some thick metal bar stock halfway in the box as well to help attenuate that annoying resonance.
No PAC is as efficient as a room unit, no matter how well it is sealed, but one thing I imagine would give it an advantage is a servo-driven flap that can mix the source of condenser air based on the rate at which the temperature approaches the setpoint. Keep it closed when there is a large differential, but incrementally allow more indoor air to be exhausted for condenser cooling (based on microcontroller estimation of the heat load) to expand the envelope at which the unit can most efficiently operate…
Well written Sean. The problem persists that 2 pipe units do not have a 1:1 ratio of input air to output air to remove the heat from the condenser. Most or all the air for the condenser comes from the room being cooled making a significant negative air pressure. Air must enter the room from windows or doors to the room being cooled. This air is likely hotter than room air and/or contains smoke, dust, or other irritants. In this sense one and two pipe residential units I have seen operate almost identically. The 2 pipe unit simply adds a small amount of outside air to the recycled input air feeding the evaporator. Until someone else on this thread gets the point that all the theory in the world makes no sense until an investigation is made on the actual cfm for input and output pipes, and the routing of the air through the 2 pipe PAC, you and I are wasting our time arguing with them. Danby and Haier units distributed in Canada have a very low input cfm compared to the very high output cfm.
What is your relevance if any?
It is a Joke, probably meant to help cool the jets of the participants so they will not have a melt down.
I used to live in a 8 X 56 mobile home with a wife & baby. I had only a window air conditioner for the Oklahoma heat. To cool the back bedroom and the smaller baby bed room I made a hose out of visqueen about 10 inches in diameter and hung it in front of the discharge section. Collecting about 50% of the cool air. At the small bedroom door I split it into 2 5 inch homemade tubes, one for the small bed room & one for the back bed room. Problem solved. The hose was against the wall which left room for walking one at a time down it. That was fine for us at the time.
For nasty HOA rules, put a regular window unit in a lattice box with a solid metal or plastic roof and run all the output into the room you want with a suitable sized insulated flex duct hose. If you have plantings to help hide the box, so much the better… A big 220 volt , 26,000 BTU window unit can cool a lot of space or the little 110 volt extra quiet 5- 10 K ones will do a room just fine IMO. The new stuff is much quieter than the ones from 1966.
YMMV
If you get a 1 pipe unit buy 1 for the room size and load, And a second for the hot air infiltration from the big exhaust fan you just installed. So which is more efficient ???
One unit or two units. HMMMMMM Need a calculator for that one:)
This reply addresses the situation much better than the comments following the video, which illustrates the ‘conversion’ of a single-pipe model to a dual (actually, triple) pipe model.
One viewer complains his converted portable ‘overheated’ to the point he had to remove the conversion.
I think most portable models depend, by design, on pulling pre-cooled air over the compressor, high-pressure line, and through the condenser to prevent the interior mechanical components and case itself from overheating – to the point the portable A/C unit would begin to resemble an ‘electrically-powered radiator’.
This would vary according to the outside air temperature and placement of the intake hose, relative to the condenser-side exhaust hose. In the video, the intake and exhaust are in fairly close proximity, and I suspect the intake air is considerably hotter than the ambient outdoor temperature.
The person who did the video may have had an exceptionally well-designed portable unit …
This reply ‘hits the nail on the head’.
On another forum, one dual-pipe user pulled the case off his unit, to see what was going on.
He observed that on his unit, the air intake hose … :smack: … simply entered into the interior of the case, without any baffling whatsoever to confine its air-flow to the condenser! So of course the condenser was free to draw most of its air from the ‘path of least resistance’ – or, directly from the room, just like with the single hose models.
I don’t think you’ll find that detail in the advertising. You’d have to disassemble each portable A/C in the showroom, before buying it.
So, you can’t base your buying decision on physics and air-conditioning theory alone, when the products are made like this! You don’t always get what you pay for … the double hose models are usually more expensive. :dubious:
Is it just me or is there’s something really strange about this thread?