Cheap duct refrigerant cooling coil with external air conditioning unit
Cheap duct refrigerant cooling coil with external air conditioning unit
(OP)
Hi,
I would like to build my own cooling system by buying cheaper individual components (China), rather than paying for very expensive out of the box AHU solutions that charge insane up to 20x more just beacause of company name. I know how to do the ducting, install the fan and the filter, and all I need to do now is to build/buy a reduction from the rectangular section of the cooling coil to circular section of the ducts. Then I believe I have to link the cooling coil to an exterior unit, which cools the refrigerant passing through the cooling coil. I basically want to do a clasic split air conditioning system but without the split, instead using a duct cooling coil so I can distribute the cold air evenly throughout my space, without having to endure local high speeds from the split unit and uneven temperature distributions/delay.
So I was wondering if someone else tried it, that is to buy separate components and then weld the cooling coil with the exterior unit. Maybe modified second hand split air conditionend systems ?
About the automation I'm thinking that the outdoor unit should have an out of the box setting for refrigerant upper/lower temperature starting or closing the compressor. Regarding the fan I'm thinking to control it via basic indoor temp sensor. The part I haven't figured out is how to link the exterior unit on/off switch to the temperature sensor working in tandem with the fan.
Thanks!
I would like to build my own cooling system by buying cheaper individual components (China), rather than paying for very expensive out of the box AHU solutions that charge insane up to 20x more just beacause of company name. I know how to do the ducting, install the fan and the filter, and all I need to do now is to build/buy a reduction from the rectangular section of the cooling coil to circular section of the ducts. Then I believe I have to link the cooling coil to an exterior unit, which cools the refrigerant passing through the cooling coil. I basically want to do a clasic split air conditioning system but without the split, instead using a duct cooling coil so I can distribute the cold air evenly throughout my space, without having to endure local high speeds from the split unit and uneven temperature distributions/delay.
So I was wondering if someone else tried it, that is to buy separate components and then weld the cooling coil with the exterior unit. Maybe modified second hand split air conditionend systems ?
About the automation I'm thinking that the outdoor unit should have an out of the box setting for refrigerant upper/lower temperature starting or closing the compressor. Regarding the fan I'm thinking to control it via basic indoor temp sensor. The part I haven't figured out is how to link the exterior unit on/off switch to the temperature sensor working in tandem with the fan.
Thanks!





RE: Cheap duct refrigerant cooling coil with external air conditioning unit
RE: Cheap duct refrigerant cooling coil with external air conditioning unit
I have made a more self explanatory sketch for better understanding:
My doubts are at 1,2,3:
1: I suppose the fan should have some sort of connection for the on/off button to the controler. Do all have or might I just buy the wrong fan ?
2: I don't have a clue on how to connect the exterior unit with the temperature sensor such that the unit (aka compressor/unit fan/laminator) will turn off in tandem with the fresh air fan. Do I need a two conection sensor ?
3: Are there any exterior units to be baught without the interior split unit or must I buy a SH one and modify it myself ? What about the heating mode (reversed refrigeration cycle), can that be manually turned off so that the unit will work only on cooling ?
*4: Any alternatives cheaper/simpler than this are appreciated.
Thanks for your responses!
RE: Cheap duct refrigerant cooling coil with external air conditioning unit
I used one of this company's multiposition air handlers:
http://www.adpnow.com/product-literature/?link=air...
The air handler is mounted horizontally in my attic, with spiral pressure ducting as headers and 6" insulated flex running down to each outlet diffuser- the adjustable circular ones are a good idea, because they can be sealed up tight in winter. I insulated the HELL out of the ducting and air handler so I don't lose too much precious cooling in the unconditioned attic space.
Note that the air handler I used is a "normal" unit, meant for normal sized ducting. There are high pressure units which are intended for use with ducting that can be snaked through existing wall and ceiling spaces etc., but of course the heat of compression from that high pressure fan is an efficiency hit. I would imagine these units would be noisy too.
The air handlers can be fitted with hydronic coils instead of evaporator coils if you want to ruin your hydronic system by adding forced air heating to it and all the associated disadvantages that come with it.
The reversed refrig cycle is an air-sourced heat pump arrangement that the mini-split compressor/condenser units that are typically paired with ductless fan-coils typically offer as standard. However, I didn't use a mini-split compressor/condenser as they're expensive and have a poor SEER relative to the larger outdoor units. I used a regular compressor/condenser unit which is typically coupled to a coil in a natural gas furnace, made by Keeprite if I recall correctly- it has worked very well for five or six years so far, so we'll see how long it lasts. The outdoor units typically used with gas furnaces can be configured for heating as an air source heat pump, but that adds cost and complexity. It would be handy for heating during the "shoulder" seasons if your off-peak electricity is cheap enough, but for me the payback versus using my modulating condensing boiler for heating would have been well over ten years- just wasn't worth the bother.
RE: Cheap duct refrigerant cooling coil with external air conditioning unit
RE: Cheap duct refrigerant cooling coil with external air conditioning unit
The outdoor unit will cycle on and off as the thermostat tells it to, unless you go for a variable speed unit, and frankly I'm not sure how those are controlled. The TXV will regulate refrigerant flow to the coil to maintain a certain amount of superheat in the vapour leaving the coil, which reduces the load on the compressor and saves energy relative to a plain orifice. Temperature control inside the house in a normal A/C system is on-off, using a simple switch-type thermostat.
The outdoor unit is always over-sized except for the peak demand (highest design differential temperature between indoor and outdoor) when it will run continuously. The key is to pick an indoor unit matched to the needs of our outdoor unit. You also need to pick an outdoor unit which doesn't have vastly more compressor/condenser capacity than you really need, otherwise it will "short cycle"- it will run only for brief periods and hence allow too few air exchanges over the coil before it shuts off again to do a decent job of dehumidification- and in my climate, humidity is the thing you really need to control to be comfortable. Most HVAC people over-size units because they think that will make owners happy- it will cool the house off from a peak temperature much faster of course, as well as handling the hottest day or two you encounter every year without allowing the temperature to rise much above setpoint- but then it will do a crappy job of maintaining temperature and humidity level for the entire rest of the year.
RE: Cheap duct refrigerant cooling coil with external air conditioning unit
(0)outdoor
(1)-> main circular duct
(2)-> filter (round fittings)
(3)-> in-line axial fan (round fittings)
(4)-> cooling coil (round fittings) with two pipes going out of it (in-out for refrigerant)
(5)-> pipes go to exterior unit (basic heat pump cycle unit)
(6)-> adjustable air inlets for achieving confortable air speeds
(7)-> temperature controller
Each of these components is an individual object, no box, no premade stuff, just bought of alibaba or something.
Fitting them together with circular piping is easy.
More problemaic are:
(4) -> welding cooling coil pipes to exterior unit pipes (hire a specialist). Afraid of refrigerant spilling with time.
(5) -> couldn't find where to buy individual exterior unit from. thinking of buying a second hand one that comes with that interior split unit (which I don't need, throw that away)
(5) -> what kind of controller outputs/signals will such outdoor unit have ? can't seem to grasp how it works (automation-wise) and how can I connect it/modify it to a simple controller to fit my needs.
(7) -> simple analog thermostat which I turn and then the system goes full-blown with cold air. (haven't got this figured out without a sketch, again figuring out controllers)
I've calculated the cooling load so choosing the cooling coil and the exterior unit shouldn't be a problem (7.5 kW/24000 btu for both the capacity of the coil and exterior unit since pipe heat losses are neglijable)
Thanks for your answers moltenmetal but since I'm not native english speaker and maybe just plain stupid, I would need simpler pinpoint explanations.
Cheers!
RE: Cheap duct refrigerant cooling coil with external air conditioning unit
Ideally I would have that remote control still in use, so I can use the system for heating aswell, so I can undersize my radiator heating system, but I don't know how to do that also, or if it's possible without the split itself...
RE: Cheap duct refrigerant cooling coil with external air conditioning unit