Heat Pump Water Heater - Coil in Tube - Page 5

jeff5may · 11-03-14, 03:49 PM

Since the size and capacity of your has changed, your cap tube is now incorrectly sized. I suggest replacing it with a txv that matches the capacity of the compressor. It will instantly solve your mismatch woes. I have had good luck with the danfoss and Emerson/alco brands made for HVAC system usage. They abound on eBay for next to nothing.

vwhead77 · 03-12-15, 07:33 AM

Liked the idea of coil inside the tube but found it frustrating to try to seal the PVC jacket. Went to copper X copper exchange with coil on the outside of the water jacket - this was close but did not get the amountof heat transfer i had hoped for. This final model is 4' of 2" copper with 24' of 1/4" copper fabricated as a home-made coil - inserted inside the 2" as shown. A slight modification to my closed water loop is needed to accomodate the larger model but all is looking good so far

Ron342 · 03-12-15, 11:43 AM

That will work better for you I think. I had wondered if the compressor heating you were worried about was due to feeding a large compressor into 1/4 tubing - this may have less resistance but still 1/4". I am hooking up a similar system using about 20 ft of 1/4 tubing wrapped around and soldered to 3/4 tubing with all inside 5 ft of 1.5" tubing mounted vertically beside the water heater tank. I will use water from a solar tank up the center tube as and alternate heat in summer and thermosyphon or pump the dhw thru the annular space between the 3/4 and 1.5 " tubes as in the pics. I have a 7500 r22 compressor and wondered if it was too big for the 1/4 tubing as well.
I see you have your r290 entering and leaving at the top as I plan on doing but I wonder why Niohaomike advised in at the top and out at the bottom?

vwhead77 · 03-12-15, 07:58 PM

Yes, I was actually looking at your .pdf drawing of this. Very interesting. I have since downgraded that A/C compressor to a 5000 BTU which did have 1/4" condensor tubing. I measured the coil and came up with my 24'length requirement. One of the problems I see happening is that I'm using this in an indirect Water heater - so the hot water keeps recirculating which of course makes my high side temp./pressure very hot. with this R290 though, it seems to hold up fairly well- I'm still able to maintain a 54 deg. discharge temp on the evap side. - this is in my dank basement so the dehumidification is welcome. I'm aactually going to pay very close attention to the pressures when I hook this one up

jeff5may · 03-12-15, 08:45 PM

Both of these designs are super awesome! IMHO, both of these HX rigs will be able to whoop out two tons of heat transfer through 1/4 inch tubing. They both look overbuilt and should last for decades. Good job, guys!

The statement Mike made was for the helical-type condenser like Ron built. Gas goes in up high, liquid falls and comes out down low. In a thermosiphon rig, this would also follow the temperature gradient induced in the HX, so the coolest liquid possible would exit at the bottom. With the linear arrangement that vwhead has employed, it could be argued that not as much subcooling would occur, since the refrigerant changes direction with regard to the flow of water. I believe it will work better than expected and much better than previous rigs. Why split hairs, what's an extra 5 or 10 watts when you're saving 1000 already?

vwhead77 · 03-14-15, 09:09 AM

We'll see what happens. I have to modify my HW loop (again) to accomodate the longer pipe - plus the unions and ball-valves - can never underestimate the convienence of those components - makes for easy removal/cleaning/ replacing if necessary. Should have it completed in the next few days if I don't get too busy (I am a local refrigeration mechanic)

vwhead77 · 04-10-15, 05:24 PM

Took the time to put it all together today. I am VERY pleased. I am getting 20 to 21 degrees increase over the new design. I charged the unit using amp draw mostly as my guide as my first attempt went off the charts and actually overloaded the compressor. Not used to r-290a pressures - but now it seems to be running perfectly - with 225 psi High-side / 20 psi low side and still putting out 52 degree DA at the evaporator - kind of strange to me but hey, it's working at 4.5 amps. I am soooo psyched. 3rd time is a charm

Thanks to all for the input over the course of this experiment.

Ron342 · 04-11-15, 08:45 AM

Congratulations & Great work!
If you know the water pump flow rate you can figure the efficiency coefficient from the temp rise vs watts. If not you can see how long it takes to come from whatever your start cold tank temp is to your cutoff tank temp, then figure that against amps x voltage over the time it took.
Be sure to get some temp and pressure cutouts (off some of those heat pumps you junk!)and put then on that puppy before you leave it alone!
Are you using the stock cap tube? And what temp is your basement air going in?
This will get me to work finishing mine!

vwhead77 · 04-11-15, 10:28 AM

Yes, I am still using the original cap tube. I do like the idea of using a TXV as per Jeff5may's suggestion. My ambient air temp is 62 degrees so the temp drop across the evap is minimal - I was more concerned about holding a steady discharge pressure and still keeping the amp draw down. Very interesting how the Low side is reacting- the sub-cooling is very strange - thus the TXV solution for sure. A tweak here and there.

Ron342 · 04-11-15, 02:19 PM

The temps you show are in and out refrigerant temps at the condenser not water? Wonder how it would act if you pushed it to 130 F high side. But 20 psi suction seems low = -6 degrees F. Did you just add charge til the amp draw increase leveled off or??
I have a 3/4 ton ebay txv for mine - it was $25 shipped but it is external equalized and I know nothing about txvs!
I wonder why no one seems to use r134 in these - is the oil not compatible - the p/t seems better.

03-12-15, 07:33 AM	#42
vwhead77 Helper EcoRenovator Join Date: Jan 2013 Location: Watkins Glen, NY Posts: 48 Thanks: 19 Thanked 5 Times in 5 Posts	Final Model - after 2 prototypes Liked the idea of coil inside the tube but found it frustrating to try to seal the PVC jacket. Went to copper X copper exchange with coil on the outside of the water jacket - this was close but did not get the amountof heat transfer i had hoped for. This final model is 4' of 2" copper with 24' of 1/4" copper fabricated as a home-made coil - inserted inside the 2" as shown. A slight modification to my closed water loop is needed to accomodate the larger model but all is looking good so far Attached Thumbnails Last edited by Daox; 03-12-15 at 11:44 AM..

03-12-15, 11:43 AM	#43
Ron342 Apprentice EcoRenovator Join Date: Feb 2010 Location: Maryland Posts: 120 Thanks: 26 Thanked 12 Times in 8 Posts	That will work better for you I think. I had wondered if the compressor heating you were worried about was due to feeding a large compressor into 1/4 tubing - this may have less resistance but still 1/4". I am hooking up a similar system using about 20 ft of 1/4 tubing wrapped around and soldered to 3/4 tubing with all inside 5 ft of 1.5" tubing mounted vertically beside the water heater tank. I will use water from a solar tank up the center tube as and alternate heat in summer and thermosyphon or pump the dhw thru the annular space between the 3/4 and 1.5 " tubes as in the pics. I have a 7500 r22 compressor and wondered if it was too big for the 1/4 tubing as well. I see you have your r290 entering and leaving at the top as I plan on doing but I wonder why Niohaomike advised in at the top and out at the bottom? Attached Thumbnails

04-10-15, 05:24 PM	#47
vwhead77 Helper EcoRenovator Join Date: Jan 2013 Location: Watkins Glen, NY Posts: 48 Thanks: 19 Thanked 5 Times in 5 Posts	It's Working!! Took the time to put it all together today. I am VERY pleased. I am getting 20 to 21 degrees increase over the new design. I charged the unit using amp draw mostly as my guide as my first attempt went off the charts and actually overloaded the compressor. Not used to r-290a pressures - but now it seems to be running perfectly - with 225 psi High-side / 20 psi low side and still putting out 52 degree DA at the evaporator - kind of strange to me but hey, it's working at 4.5 amps. I am soooo psyched. 3rd time is a charm Thanks to all for the input over the course of this experiment. Attached Thumbnails

04-11-15, 08:45 AM	#48
Ron342 Apprentice EcoRenovator Join Date: Feb 2010 Location: Maryland Posts: 120 Thanks: 26 Thanked 12 Times in 8 Posts	Wow! Congratulations & Great work! If you know the water pump flow rate you can figure the efficiency coefficient from the temp rise vs watts. If not you can see how long it takes to come from whatever your start cold tank temp is to your cutoff tank temp, then figure that against amps x voltage over the time it took. Be sure to get some temp and pressure cutouts (off some of those heat pumps you junk!)and put then on that puppy before you leave it alone! Are you using the stock cap tube? And what temp is your basement air going in? This will get me to work finishing mine!

11-03-14, 03:49 PM	#41
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,431 Thanks: 431 Thanked 619 Times in 517 Posts	Since the size and capacity of your has changed, your cap tube is now incorrectly sized. I suggest replacing it with a txv that matches the capacity of the compressor. It will instantly solve your mismatch woes. I have had good luck with the danfoss and Emerson/alco brands made for HVAC system usage. They abound on eBay for next to nothing.

03-12-15, 07:58 PM	#44
vwhead77 Helper EcoRenovator Join Date: Jan 2013 Location: Watkins Glen, NY Posts: 48 Thanks: 19 Thanked 5 Times in 5 Posts	Yes, I was actually looking at your .pdf drawing of this. Very interesting. I have since downgraded that A/C compressor to a 5000 BTU which did have 1/4" condensor tubing. I measured the coil and came up with my 24'length requirement. One of the problems I see happening is that I'm using this in an indirect Water heater - so the hot water keeps recirculating which of course makes my high side temp./pressure very hot. with this R290 though, it seems to hold up fairly well- I'm still able to maintain a 54 deg. discharge temp on the evap side. - this is in my dank basement so the dehumidification is welcome. I'm aactually going to pay very close attention to the pressures when I hook this one up

03-12-15, 08:45 PM	#45
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,431 Thanks: 431 Thanked 619 Times in 517 Posts	Both of these designs are super awesome! IMHO, both of these HX rigs will be able to whoop out two tons of heat transfer through 1/4 inch tubing. They both look overbuilt and should last for decades. Good job, guys! The statement Mike made was for the helical-type condenser like Ron built. Gas goes in up high, liquid falls and comes out down low. In a thermosiphon rig, this would also follow the temperature gradient induced in the HX, so the coolest liquid possible would exit at the bottom. With the linear arrangement that vwhead has employed, it could be argued that not as much subcooling would occur, since the refrigerant changes direction with regard to the flow of water. I believe it will work better than expected and much better than previous rigs. Why split hairs, what's an extra 5 or 10 watts when you're saving 1000 already?

03-14-15, 09:09 AM	#46
vwhead77 Helper EcoRenovator Join Date: Jan 2013 Location: Watkins Glen, NY Posts: 48 Thanks: 19 Thanked 5 Times in 5 Posts	We'll see what happens. I have to modify my HW loop (again) to accomodate the longer pipe - plus the unions and ball-valves - can never underestimate the convienence of those components - makes for easy removal/cleaning/ replacing if necessary. Should have it completed in the next few days if I don't get too busy (I am a local refrigeration mechanic)

04-11-15, 10:28 AM	#49
vwhead77 Helper EcoRenovator Join Date: Jan 2013 Location: Watkins Glen, NY Posts: 48 Thanks: 19 Thanked 5 Times in 5 Posts	Yes, I am still using the original cap tube. I do like the idea of using a TXV as per Jeff5may's suggestion. My ambient air temp is 62 degrees so the temp drop across the evap is minimal - I was more concerned about holding a steady discharge pressure and still keeping the amp draw down. Very interesting how the Low side is reacting- the sub-cooling is very strange - thus the TXV solution for sure. A tweak here and there.

04-11-15, 02:19 PM	#50
Ron342 Apprentice EcoRenovator Join Date: Feb 2010 Location: Maryland Posts: 120 Thanks: 26 Thanked 12 Times in 8 Posts	The temps you show are in and out refrigerant temps at the condenser not water? Wonder how it would act if you pushed it to 130 F high side. But 20 psi suction seems low = -6 degrees F. Did you just add charge til the amp draw increase leveled off or?? I have a 3/4 ton ebay txv for mine - it was $25 shipped but it is external equalized and I know nothing about txvs! I wonder why no one seems to use r134 in these - is the oil not compatible - the p/t seems better.