AC or water chiller for climate control?

chill water can remove humidity in exactly the same manner that a direct expansion coil can... you just need a different coil geometry or colder water.

its exactly the same principal as a split vapor compression evaporators.

again though, chilling water has nearly 0 efficiency gains at these small scales.

How many cooling tons do you need to be at where chilled glycol becomes more efficient than split vapor?

you really start to see astonishingly efficient chiller plants above 100 tons.

but thats more to do with high end variable speed circulation pumps... fancy magnetic bearing centrifugal compressors and cooling tower fans w/ variable pitch props etc. these systems are like engines ... the gains in efficiency tend to scale favorable the larger the equipment gets.

you also have to remember that chill water is also much much much more practical than trying to build ducts w/ like 25 square feet of cross section to carry 100 tons of 55 degree air.

at these small scales, the gain you can expect is from the lower power required to circulate water verses air. were talking about like 1/4hp to circulate water( low assumption for sake of argument), and a 1/8hp fan to push air through the fan coil.
this is as opposed to a 1/2hp to 3/4hp blower to move air( 4 tons to 5 tons).

that is a difference of around 100-200 watts maximum if we are super super generous.

problem is though, 99% of these chiller systems are literally just modified condensing units using off the shelf plate or coaxial heat exchangers and hence are not optimized for chilling water...

they want to charge like 10 grand for these systems... and they are generally not even VRF systems ( variable speed units like the Mr. slim).

i really dont get where this myth came from. yes FFS, water is indeed a better conductor of heat... but this is why your average evaproator coil has like 100x the surface area of a coax heat exhchanger lol.

if one of the big manufacturers really wanted to, you could definatly build a good small chiller for a price near to a conventional condensing unit + air handler, but as it stands they just cost way to much to justify the small gains in efficiency.

Exactly. I highly suggest building a chiller from a dehumidifier. Takes all of about 20 minutes and please believe, it worked better than two 1/2hp chillers put together. Quicker at cooling and more cooling as well. Not to mention more guiet

I was bouncing ideas back and forth with my buddy today who's an AC tech. I think what would be cool for a tinkering type would be to have a 2 stage system. It would be ducted but no makeup air from outside, just an air handler in mechanical space and split compressor setup outside. You stack 2 case coils coming off the top of the handler. Stage 1 is chilled glycol/ water where the outside unit is fan blowing cold ambient air across heat exchanger. You can wire the pump thermostatically to come on only when outside air is below a certain point. Stage 2 is standard split refrigerant. So if wired properly your system uses more and more of the glycol side as seasons get colder. In the summer it would be all refrigerant. Therefore your not technically using refer to chill water, this system could save pretty good money in colder climates. I know where I'm at in maine you get nights in the 50s even in the summer. If you ran your lights at night here you could probably run just chilled water side October to late April

dwiz415 said:

Exactly. I highly suggest building a chiller from a dehumidifier. Takes all of about 20 minutes and please believe, it worked better than two 1/2hp chillers put together. Quicker at cooling and more cooling as well. Not to mention more guiet

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probably aquarium chillers... idk why they rate them in fractional HP.

what is the HP exactly? the amount of work being done or the HP of the compressor? never understood that.

if you convert HP to watts assuming 100% efficiency, you get to 750 watts per 1HP... im your aquarium chillers are not even that powerful though.

750 watts would translate to around 3kbtuh which is piss small. if you reduce that figure by 25% for a more realistic figure... its even pissier.

your average dehuy is in or around a smaller size window ac... so anywhere from 6kbtuh to 12kbtuh.

coldcanna said:

I was bouncing ideas back and forth with my buddy today who's an AC tech. I think what would be cool for a tinkering type would be to have a 2 stage system. It would be ducted but no makeup air from outside, just an air handler in mechanical space and split compressor setup outside. You stack 2 case coils coming off the top of the handler. Stage 1 is chilled glycol/ water where the outside unit is fan blowing cold ambient air across heat exchanger. You can wire the pump thermostatically to come on only when outside air is below a certain point. Stage 2 is standard split refrigerant. So if wired properly your system uses more and more of the glycol side as seasons get colder. In the summer it would be all refrigerant. Therefore your not technically using refer to chill water, this system could save pretty good money in colder climates. I know where I'm at in maine you get nights in the 50s even in the summer. If you ran your lights at night here you could probably run just chilled water side October to late April

Click to expand...

yea what you are describing already exists only its geared towards hot water systems and not cold water.

basically the heating coil is in parallel or in serial with the evaporator, and the hot water is zoned just any generic hydronic system with an aquastat and mixing valve or valve actuator and thermistor.

problem is, to do what you propose with cold water will be very expensive unless you have a very good place to sink t he heat from the grow room... like a pond or a big deep trench to burry a bunch of coiled up pipe.

the amount of heat you can move is a function of( among many other things) the temperature difference from the sink an source.

in your case... the outdoors would be your sink, and the source of the heat would be your room.

when your room is 80, and your outdoors is only 50f, you are going to need a heat exchanger like 10x larger(just guessing here) than if the outdoor temps were say... 0 degrees f.

this means in order to have it able to run at 50f you need to pay out the ass for a massive heat exchanger and because of the heat exchanger size you need a massive set of fans or pumps AND a staging system to modulate the fans/pumps speed or multiple small fans/pumps that you can turn off and on.

i think if you sit down and look at the economics of this, you will find that such a system will never pay for itself.

you would be far better off just using an economizer system to bring in outside air directly via a damper and enthalapy sensor.

this means you would be wasting co2 i guess... but again look at the economics. how much are you paying to for co2 verses the electricity you save? im guessing it makes 100% sense to just bring in outside air and just produce more co2.

if you want to get crazy... you could buy a set of heat recovery ventilators, but these units are not designed for large volumes of air and tend to be very very expensive.