I’m looking at replacing my heat pump. For the back story, I currently have a Rheem Classic Plus heat pump which is a 3-speed inverter type ODU (RP17) matched to a 2-speed air handler (RH2) with a Rheem communicating thermostat. The unit is 5 years old and was put in by the builder. I won’t bore anyone with the details as to why my builder put in a higher end inverter unit such as this but will say I spec ’ed a 2-stage system.
This system has been nothing but problems for 5 years. I have had the main inverter control board replaced, communicating board replaced, air handler mounted breaker for the heat strips replaced, ODU coil leaked and replaced, temperature sensors replaced, and main smart thermostat replaced. While the parts are under warranty, I have paid a lot in labor for these repairs and parts are only under warranty for 5 more years. I have been out of service for weeks at a time during cold weather and on the heat strips while waiting on parts. I am currently down and waiting on parts as the ODU freezes up and won’t go into defrost mode. This problem has been diagnosed by the technician and Rheem tech support as an ODU temperature sensor for the on demand defrost. Per the indoor smart thermostat, the ODU coil temperature is now at 157 degrees and the unit is off and has been reading as high as 250 degrees, thus no call for defrost.
I’m done with this and looking at replacing the system. I have a 2715 sq ft house in central Virginia. My house is only 5 years old so newer construction with insulation to code and a normal number of windows but more on the front and the house does face due west so afternoon sun during the hottest part of the day. It is one story plus a room over the garage. The fan coil is in the attic so some loss from the ducts. The ducts seem to be fine and confirmed by my dealer, I have even temperatures throughout the house except the room over the garage which does stay a little warm in the summer, but I don’t use it much and may address this later. Design temperatures for my area are 95 and 18.
I realize the 5-ton unit is probably oversized but since the current unit is a 3 speed with a 2-speed air handler it can run at lower speeds at times to keep humidity in check during the summer and has a lot of capacity for heating in the winter especially when in overdrive (heating mode only). I have the heat strips locked out above 30 degrees and it heats fine, at least when it’s working. My only complaint is, when it is quite cold, the temperature per the stat will sometimes drop up to 2 to 3 degrees from set point before it catches up. It seems like the ODU stages up by time instead of demand. I can watch it stage up from the smart thermostat.
When replacing the unit, I want to use the same dealer I have used for 20 years which is not the same dealer the builder used to put in the Rheem. My dealer is also doing the repairs on my Rheem. I used my same dealer to put in 2 systems in my previous house. They put in a Carrier heat pump with a Carrier gas furnace hybrid system for my downstairs and a 2-stage Carrier heat pump for my upstairs both with Carrier Edge thermostats. Both systems worked fine for many years.
After much research, I asked the dealer to quote a Carrier 25HCB6 2-stage ODU AHRI matched to a FV4 variable speed fan coil non communicating system. Some may feel like I’m going backwards in technology but I liked the Carrier 2-stage in my former house, and I want less complexity with fewer things to go wrong and fewer proprietary parts to have sourced and expensive to buy when out of warranty.
The dealer wants to keep the new unit at 5 tons based on the sq ft. I asked and they do not do Manual J calculations. I’ve read on here in guest posts where some dealers don’t do measurements, and hence some of these may just guestimate the Manual J numbers anyway. I asked about a 4-ton unit, and they didn’t want to do this. I assume they worry about being responsible if it turns out to be too small. I probably could insist on a 4-ton and accept responsibility if it turns out to be too small. My thinking is at least with the 2-stage 5-ton unit it will run in the first stage most of the time in the summer at, per the specs, 67% of capacity so at about 3.35 tons and I will have more heating capacity for the winter. This is a lot like my existing unit. If anyone has any thoughts on this, I would love to hear them.
Another thing I liked about the FV4 fan coil is that it can run in a Super Dehumidify mode if no call for cooling but a call for dehumidification exists if set up and optioned with the Carrier Edge thermostat. This is not just the overcool mode used by many systems and thermostats and overcool can also be set up by the Carrier Edge if desired. Per the specs, the Super Dehumidify mode signals the fan coil to run at “minimum airflow for maximum humidity removal and will cycle the equipment at 10 min on and 10 min off until humidity is satisfied”. The specs also said that Super Dehumidify will lower the airflow to 50% of cooling. I looked at the Ecobee thermostat sold by Carrier, but it only has a dehumidify overcool mode by up to 3 degrees and Carrier’s Infinity thermostats are only for communicating systems or traditional wiring for single speed systems. I also like that the Edge can be optioned to start in stage 2 above or below a selectable temperature when equipped with the outdoor temperature sensor. As I mentioned before, I have a complaint with my current system dropping to far below the set point at times when heating before catching up. The Ecobee also cannot be paired with an outdoor temperature sensor but relies on the internet for the outdoor temperature.
Does anybody know of a more advanced thermostat that will work with Carrier and support the Super Dehumidify and stage-2 start feature? I like the idea of Wi-Fi, remote access and computer programming of the stat but will stick with the Edge if needed.
Now for a more technical question. In the Super Dehumidify mode with the 50% airflow, since the fan coil fan runs at this slower speed, I believe this will cause the TXV to close more in the fan coil slowing the flow of refrigerant. The Scroll compressor in the ODU will be in stage one (I assume) with the super dehumidify mode of the fan coil. While I understand stage one is valving and not a lower speed, does this lower TXV setting in the fan coil further lower the demand (resistance) on the compressor and use less power or is it the same power as with a normal cooling mode in stage one? I tried researching this on the net but couldn’t find anything specific to this. I did read that the TXV valves in modern higher end systems vs. the more traditional open or shut only expansion valves are one of the things that improve system efficiency, hence my thinking.
Sorry to be so long winded but thanks for reading. :pop: I appreciate any responses to my questions and any other insights. I have a general understanding of HVAC but by no means an expert. I’m just technical by nature and enjoy researching and understanding how things work. I have been following HVAC-Talk for many years and have learned a lot from the pros. Thank You!
This system has been nothing but problems for 5 years. I have had the main inverter control board replaced, communicating board replaced, air handler mounted breaker for the heat strips replaced, ODU coil leaked and replaced, temperature sensors replaced, and main smart thermostat replaced. While the parts are under warranty, I have paid a lot in labor for these repairs and parts are only under warranty for 5 more years. I have been out of service for weeks at a time during cold weather and on the heat strips while waiting on parts. I am currently down and waiting on parts as the ODU freezes up and won’t go into defrost mode. This problem has been diagnosed by the technician and Rheem tech support as an ODU temperature sensor for the on demand defrost. Per the indoor smart thermostat, the ODU coil temperature is now at 157 degrees and the unit is off and has been reading as high as 250 degrees, thus no call for defrost.
I’m done with this and looking at replacing the system. I have a 2715 sq ft house in central Virginia. My house is only 5 years old so newer construction with insulation to code and a normal number of windows but more on the front and the house does face due west so afternoon sun during the hottest part of the day. It is one story plus a room over the garage. The fan coil is in the attic so some loss from the ducts. The ducts seem to be fine and confirmed by my dealer, I have even temperatures throughout the house except the room over the garage which does stay a little warm in the summer, but I don’t use it much and may address this later. Design temperatures for my area are 95 and 18.
I realize the 5-ton unit is probably oversized but since the current unit is a 3 speed with a 2-speed air handler it can run at lower speeds at times to keep humidity in check during the summer and has a lot of capacity for heating in the winter especially when in overdrive (heating mode only). I have the heat strips locked out above 30 degrees and it heats fine, at least when it’s working. My only complaint is, when it is quite cold, the temperature per the stat will sometimes drop up to 2 to 3 degrees from set point before it catches up. It seems like the ODU stages up by time instead of demand. I can watch it stage up from the smart thermostat.
When replacing the unit, I want to use the same dealer I have used for 20 years which is not the same dealer the builder used to put in the Rheem. My dealer is also doing the repairs on my Rheem. I used my same dealer to put in 2 systems in my previous house. They put in a Carrier heat pump with a Carrier gas furnace hybrid system for my downstairs and a 2-stage Carrier heat pump for my upstairs both with Carrier Edge thermostats. Both systems worked fine for many years.
After much research, I asked the dealer to quote a Carrier 25HCB6 2-stage ODU AHRI matched to a FV4 variable speed fan coil non communicating system. Some may feel like I’m going backwards in technology but I liked the Carrier 2-stage in my former house, and I want less complexity with fewer things to go wrong and fewer proprietary parts to have sourced and expensive to buy when out of warranty.
The dealer wants to keep the new unit at 5 tons based on the sq ft. I asked and they do not do Manual J calculations. I’ve read on here in guest posts where some dealers don’t do measurements, and hence some of these may just guestimate the Manual J numbers anyway. I asked about a 4-ton unit, and they didn’t want to do this. I assume they worry about being responsible if it turns out to be too small. I probably could insist on a 4-ton and accept responsibility if it turns out to be too small. My thinking is at least with the 2-stage 5-ton unit it will run in the first stage most of the time in the summer at, per the specs, 67% of capacity so at about 3.35 tons and I will have more heating capacity for the winter. This is a lot like my existing unit. If anyone has any thoughts on this, I would love to hear them.
Another thing I liked about the FV4 fan coil is that it can run in a Super Dehumidify mode if no call for cooling but a call for dehumidification exists if set up and optioned with the Carrier Edge thermostat. This is not just the overcool mode used by many systems and thermostats and overcool can also be set up by the Carrier Edge if desired. Per the specs, the Super Dehumidify mode signals the fan coil to run at “minimum airflow for maximum humidity removal and will cycle the equipment at 10 min on and 10 min off until humidity is satisfied”. The specs also said that Super Dehumidify will lower the airflow to 50% of cooling. I looked at the Ecobee thermostat sold by Carrier, but it only has a dehumidify overcool mode by up to 3 degrees and Carrier’s Infinity thermostats are only for communicating systems or traditional wiring for single speed systems. I also like that the Edge can be optioned to start in stage 2 above or below a selectable temperature when equipped with the outdoor temperature sensor. As I mentioned before, I have a complaint with my current system dropping to far below the set point at times when heating before catching up. The Ecobee also cannot be paired with an outdoor temperature sensor but relies on the internet for the outdoor temperature.
Does anybody know of a more advanced thermostat that will work with Carrier and support the Super Dehumidify and stage-2 start feature? I like the idea of Wi-Fi, remote access and computer programming of the stat but will stick with the Edge if needed.
Now for a more technical question. In the Super Dehumidify mode with the 50% airflow, since the fan coil fan runs at this slower speed, I believe this will cause the TXV to close more in the fan coil slowing the flow of refrigerant. The Scroll compressor in the ODU will be in stage one (I assume) with the super dehumidify mode of the fan coil. While I understand stage one is valving and not a lower speed, does this lower TXV setting in the fan coil further lower the demand (resistance) on the compressor and use less power or is it the same power as with a normal cooling mode in stage one? I tried researching this on the net but couldn’t find anything specific to this. I did read that the TXV valves in modern higher end systems vs. the more traditional open or shut only expansion valves are one of the things that improve system efficiency, hence my thinking.
Sorry to be so long winded but thanks for reading. :pop: I appreciate any responses to my questions and any other insights. I have a general understanding of HVAC but by no means an expert. I’m just technical by nature and enjoy researching and understanding how things work. I have been following HVAC-Talk for many years and have learned a lot from the pros. Thank You!
source https://hvac-talk.com/vbb/threads/2235400-Looking-At-A-New-Heat-Pump-Out-With-The-New-Technology-In-With-the-Old?goto=newpost
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