Half a croissant, on a plate, with a sign in front of it saying '50c'
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Combined AC / HRV

Simultaneous Cooling and ventilation
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Start with fresh air, from outside the building. Blow it through a heat exchanger (HX) similar to a bong cooler, except with chilled hydronic oil being sprayed in instead of water. The cool air drawn from the top of the HX is then sent into the building.

Take stale (but cool) air from inside the building. Blow it into a second bong cooler style heat exchanger. This time, though, the hydronic fluid being sprayed in is hot. The hot stale air coming out of the HX is then vented to the atmosphere.

The hydronic oil makes one single loop:

It's collected (warm) from the bottom of the fresh air HX, and pumped through the hot side of the heat pump, and sprayed (hot) into the exhaust air HX.

It's collected (cool) from the bottom of the exhaust air HX, pumped through the cold side of the heat pump, and sprayed (cold) into the fresh air HX.

The advantages are as follows:

Because the hydronic oil is much more thermally dense than air, heat can be moved between the heat pump and the oil much more efficiently than directly between the heat pump and air. This means that the sealed system's heat exchangers can be made smaller, which means lower cost for the same efficiency.

By spraying the oil in a way that produces very small droplets, the area of contact between the oil and the air inside the heat exchangers can be very large, allowing a very high rate of heat exchange between the oil and the air. Plus, since the oil/air heat exchangers are very simple, consisting mostly of a big plastic tube, their cost is low.

Another advantage is that it can be switched from a home cooling effect to a home heating effect, by changing the flows of hydronic oil, without having to change the flow of refrigerant. Since the oil is close to atmospheric pressure, and refrigerant generally is not, this is a cheaper way of switching the heating/cooling function of the heat pump than the conventional manner (which would be to use valves to switch the functions of evaporator and condensor).

If condensate (water) mixes in with the oil, that's not a problem, since it will simply be heated by the heat pump, and sprayed into the exhaust HX, where it will evaporate, helping to cool the oil that it was sprayed in with.

The comfort advantage of this over a regular air conditioner is, of course, that the air is fresher.

goldbb, Aug 17 2009

Description of a Bong Cooler http://en.wikipedia.org/wiki/Bong_cooler
[goldbb, Aug 18 2009]


       I would argue that this is actually a less efficient system for cooling air than the current partial or complete displacement refrigeration systems. Furthermore you would make a far better impression if you didn't use the word "bong" repeatedly in your post, leading to the impression that the idea occurred to you while you were getting high. Your water pipe may seem ingenious when it is getting you high, it is otherwise quite unremarkable.
WcW, Aug 17 2009

       If say that you "would" argue that this is less efficient than a regular air conditioner... then do it! :)   

       Be specific, and tell us why you believe my idea for a combined air cooler and heat recovery ventilator is less efficient than an air cooler and heat recovery ventilator that are seperate devices.   

       (Perhaps you are of the belief I would foolishly use a hydronic oil with a lower specific heat capacity and thermal conductivity than air? Or, perhaps you believe that for equal costs, a fine mist of oil falling through a plastic tube will have less surface area than a coil of metal tube.)   

       Perhaps you could suggest a better name for that particular type of heat exchanger? I came across it while looking at Wikipedia's "Cooling technology" category, and was made curious by the name. After reading the description, I realized it was an excellent form of heat exchanger for what I wanted to accomplish.
goldbb, Aug 18 2009

       It's fear-inducing that at the bottom of the linked page there's this text:   

       External links:   

       Beginners Guide To Bongs   

       Nuclear Tower Water Cooling   

       Granted the link goes to computer-cooling bong tech data, but still...
normzone, Aug 18 2009

       since the words "bong" and "HVAC" don't co-occur in many technical websites I infer that it isn't an actual industry terminology.   

       Oil wouldn't function in an evaporation cooler.   

       How does adding the additional stage increase the efficiency over a conventional cooling system?
WcW, Aug 19 2009

       //Hydronic oil// seems an oxymoron, as hydronic implies water (not oil).
spidermother, Aug 19 2009

       WcW, a bong cooler is typically a computer cooling device. If you do a quick google search for "bong cooler", you'll get about 146,000 hits, of which the first several pages are all about computer cooling.   

       Oil won't function in an evaporative cooler, but, if the oil has been chilled (by a heat pump), it will nonetheless cool the air through which it is being sprayed. That's why I said, "Blow it through a heat exchanger similar to a bong cooler", not "Blow it through a bong cooler."   

       As for efficiency: If the original system you're comparing it to is a conventional AC, together with a conventional HRV, then...   

       In the original system, the partly-cooled air from the HRV is circulated into the room, mixing with the room's air. The mixture of stale room air and fresh air circulates around the building, with some of it being circulated through the cold side of the heat pump. Meanwhile, a portion of this air mix is continously evacuated through the HRV to the atmosphere. The air circulates through the system several times. Any dust that's not caught by the machinery's air filter is circulated into the room, and breathed by the occupants. Odors are also circulated through the building.   

       Also, in a conventional AC+HRV system, since no heat exchanger is 100% efficient, the air that's exhausted to the atmosphere by the HRV is below atmospheric temperature... but this cool air isn't used to help cool the hot side of the heat pump, it's just discarded.   

       With my system, fresh air is brought in. It's cooled, partly using the coolth of the air that was exhausted, partly using the heat pump. The air makes one single pass through the building. The coolness of the air is recovered (by transferring it to the oil), and the air is vented to the atmosphere.   

       Energy efficiency is no less, capital costs are less, but air quality is improved.   

       spidermother, it seemed like the right word to use... maybe "thermal oil" would be more betterer?
goldbb, Aug 19 2009

       yeah, got that part but my question was:   

       How is this better than a total loss HVAC where the vented air is used to cool the hot side of a heat pump, or passed through a heat exchanger at the inlet/outlet. Generally total loss systems are used where there is need for large quantities of fresh air to displace vapors or dust in industrial applications, or where evaporative cooling makes retaining cooled air impossible. Would your circulating oil vapor system be more energy efficient than a simple cross flow heat exchanger?   

       On the positive side use of a hydrostatic oil bath spray would remove particulates and might negate the need for a filter+++
WcW, Aug 20 2009

       not sure about how efficiently heat would be transferred between oil droplets and the air, my general impression is that it's not that good.
WcW, Aug 20 2009

       Sorry, what stops me breathing oily air?
wjt, Aug 20 2009

       WcW, Aren't cross flow heat exchangers less efficient than counter current heat exchangers?   

       Since air has a (relatively) low specific heat capacity and thermal conductivity, wouldn't a crossflow heat exchanger (between air and refrigerant) need to be bigger (and therefor costlier) than the heat exchanger between refrigerant and thermal oil? (I'll admit that the oil/air heat exchanger needs to be big, but since it's little more than a big plastic tube, it's cost should be low... but any refrigerant/anything heat exchanger needs to be made of metal).   

       Since the thermal oil can be pumped around at near atmospheric pressures, the pipes used can be cheap plastic, rather than costlier copper.   

       Less refrigerant would be needed, due to both oil/refrigerant heat exchangers could be located right next to the compressor. That's in addition to the savings in quantity of refrigerant due to the oil/refrigerant heat exchangers being smaller than air/refrigerant heat exchangers.   

       wjt, The oil would have a sufficiently high boiling point so that very little of it evaporates, so it shouldn't get into the air you breathe in that manner.   

       As for actual droplets of oil escaping... the oil is being sprayed downwards, while the air is being blown upwards. If the speed of the air does not exceed the terminal velocity of the droplets, the droplets will fall downward, not blow upward.   

       With a properly designed nozzle, the size of the droplets should be just barely large enough to fall, rather than be blown upwards.   

       An additional measure could be some sort of sponge or filter, as you'd have on top of a gas/liquid seperator.
goldbb, Aug 20 2009

       What is the terminal velocity of a tiny droplet in an updraft? It might be better to run the oil down through a wire matrix or wadding and absorb the heat that way since that would eliminate the need for high pressure nozzles and such. Even so, I'm not seeing a huge advantage here, short of the very good particulate filtering that you would get. Also why not make the unit a downdraft system, that would help retain the oil and reduce the amount of air induction required.
WcW, Aug 21 2009

       " What is the terminal velocity of a tiny droplet in an updraft? "   

       African or European?
normzone, Aug 21 2009


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