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Old 06-08-13, 11:08 PM   #1
NiHaoMike
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Default DIY dehumidifier/air conditioner/heat pump water heater

I noted that even during the peak of Texas summer, the cold water is still too cold to shower with, especially in the morning. So why not use a heat pump to dehumidify the house (and provide a little cooling) in order to reduce the load on the main A/C units as well as provide "free" hot water during the summer?

My plan is to start out with a 1/2HP (or so) dehumidifier or window A/C, preferably one that uses R22 since I have quite a bit of ES22A. I'm thinking of replumbing the existing condenser as an additional evaporator in order to increase efficiency. But rather than just connect it in series or parallel with the evaporator, why not use an ejector like the A/C system in the Prius uses? ( 2010 Prius first with ejector-cycle air conditioning ) I'm not exactly sure how to design the ejector, can someone point me to some resources? (I'm planning on using a MIG welding tip for the nozzle unless it's going to be the completely wrong size.)

I'll have to add in a heat exchanger and a pump. I found the following two items:
Grundfos UP15-18B5 Open System Circulator Pump, 1/25 HP, Bronze, 115V, 1/2" Sweat Mount - eComfort.com
B3-12A 40 Plate Heat Exchanger 3/4" Male NPT 7.5"x2.9"
Is that pump going to be powerful enough for this application? It's expensive but so far, it's the cheapest good quality unit I have found. The heat exchanger is on the big side but that should just result in better efficiency. I'm going to build my own variable frequency drive for the pump. (The compressor, however, isn't going to be variable frequency since that doesn't add much benefit for my use.)

I'll use variable speed computer fans for the evaporator. (I could possibly use some fancy Deltas with Cindy Wu sensorless FOC, but that would be overkill so I'll most likely just use some Panasonics I have lying around.) I might also use a pair of radiators or heater cores and a fountain pump for precool/reheat in order to enhance dehumidification, but I would first get it working and add those in only if it doesn't work well enough without them.

And instead of using a TXV, I'm thinking of using a solenoid valve. But rather than the conventional solenoid valves where the pressure difference tries to close the valve (which would result in very unstable flow modulation), the pressure difference tries to open the valve like how some transmission valves work. For example, if the worst case pressure difference is going to be 200PSI, the spring would be sized such that it would begin to open at that pressure. By varying the voltage applied to the coil, the pressure difference that opens the valve (and thus the flow rate) can be varied. (I'm very good at electronics and microcontrollers, so don't worry about the control side of things.) The nozzle in the ejector provides some resistance in order to stabilize things.

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