5 ms·

I tried like hell to install an air-to-water heat pump instead of a replacement gas boiler and it didn't make anything close to economic sense to do so. What d

I tried like hell to install an air-to-water heat pump instead of a replacement gas boiler and it didn't make anything close to economic sense to do so. What do I want from a heat-pump: I want it to work with a contact-closure (TT/XX) input to call for heat/cooling. Sure, if you have a fancy thermostat that works better, I'm going to read the brochure, but I'm not buying it if I find out it won't work with just a dry contact input. I want it to use parts that are in stock at my local HVAC supply house. I don't want to be without heat for 3+ days while some obscure custom part is shipped in from someplace across the country. I want it to have an open interface to extract data (similar to the open interface of a dry-contact closure) about run-time, performance, etc. (I will, however, buy it without this.) I want it to be sold/serviced by multiple competing suppliers in my area. (This is what ultimately undid the chance to install an A2W heat pump: only one company was in the business of supplying them and they priced it accordingly.) For a mini-split system, I want to be able to run the refrigerant and condensate lines inside the building so I don't have hideous lineset covers festooning my house. I'm happy to chat more as a homeowner interested in the space (but with a 6 month old Bosch boiler on the wall and possibly interested in the minisplit for shoulder season heating and summer cooling).

Mvandenbergh 4y ago
Nobody will build a heat-pump system with an on/off control system like that because the performance will be awful. Certainly not an air-to-water system.
- oceanplexian 4y ago
  It already exists. Check out Mr. Cool Universal and Gree Flexx. Heat pumps that work with a normal thermostat exist. Most of the info about this stuff online is trash because HVAC is the most toxic online community compared to any other contracting profession. One of the reasons highly efficient mini splits haven’t took off in the USA- the self proclaimed experts want to charge $2000 to drill a hole and charge a line set, so most people DIY.
  - thaeli 4y ago
    I've often wondered why this is. My best guess is that the EPA cert (not actually hard to get) has been turned into some sort of weird quasi-guild-membership thing. I can walk right in to a "to the trade" electrical or plumbing supply and they'll deal with me, no problem, no questions asked. With HVAC.. they won't even talk to you without an EPA number, even if you're not buying refrigerant. DTC for whole house systems, if they can make the regulatory side work and provide a good customer experience, is the most important part of this.
    - sokoloff 4y ago
      I'm a potential customer for DTC/DIY installation, but I think that's a pretty small slice of the market. Many of my friends are entirely willing to drop $4-5K for a single zone mini-split install (that's $1-1.5K of equipment and 2 hours of labor) and wouldn't dream of drilling a hole in the side of their house to save $3K.
      - abakker 4y ago
        I recently got quoted $17k for 2 zone mini split. I bought the tools, instructions, and watched youtube and spent $4500 total. At that savings, I don't need a warranty. I can just buy and install another system if it fails.
        rnk 4y ago
        Can you explain a little more what you did? Just a little bit, like what brand, did you replace an existing home system. Who did the electrical, did you need duct work? I already have a forced gas system, you can just connect it up? If I only had say 4-5 rooms on one story it would be a lot easier.
        sokoloff 4y ago
        Lots of good YouTube videos and good DIY HVAC content on garagejournal.com (the latter will have good discussion on brands as well as DIY installs). For a case where you have a ducted gas furnace, you are probably better off with a traditional A coil evaporator, especially if you want invisible in the living area of the house. Those are not as DIY-friendly (but anything is DIY-able if you're skilled and bold enough, willing to learn, and willing [or eager] to buy some tools :) ).
- thaeli 4y ago
  As a backup option, the incumbents already make this. Carrier Infinity is a good example. Proprietary protocol (RS-485 based, so it can run over existing thermostat wiring) between the smart thermostat and the furnace, and between the furnace and outside condenser unit. Even with all these smarts, there is still a fallback mode provided with a regular old dry-contacts control wires that can hook to any standard thermostat. Yeah, the system won't operate at peak performance, but it will operate, and that's very important when every HVAC tech carries a standard thermostat with them, or even uses basic jumper wires, in an emergency until they can return with correct parts.
- yencabulator 4y ago
  My Carrier wall unit has a button for manual operation: > MANUAL CONTROL is intended for testing purposes and emergency operation only.
- lsaferite 4y ago
  Heatpumps are essentially pretty dumb devices at core. They use 24v AC for control, there's a reversing valve contactor to control if it's heating or cooling, there's a contactor for the fan, and one for each stage of the pump. Maybe there's another contactor for the emergency heating element. If you are fancy you might have contactors for UV sterilization, humidification, and/or dehumidification. Literally the 'smartest' part of my HVAC system, beyond the thermostat, is the blower fan. It's a variable speed motor and has a speed controller integrated into the motor housing with multiple 'taps' that let you control the fan speed in steps. It's configurable if you have the programming hardware.
RetpolineDrama 4y ago
>but I'm not buying it if I find out it won't work with a dry contact input. But... why?
- sokoloff 4y ago
  Because it's from a new entrant to the market and I don't know that their complex interface will be available, supported, and serviceable 12 years into the 20 year lifetime of the equipment. I do know that I will always be able to provide a dry contact closure in the event they go belly-up and the thermostat goes unsupported. I have my current gas boiler working via an outdoor reset mechanism that provides flow water at 116°F to 135°F via a dry contact closure from the zone relay box. There's no reason for me to believe that Bosch (and others) can create a modulating boiler that works efficiently from just a dry contact closure input from the house (plus a flow temp sensor, a return temp sensor, an outdoor temp sensor, and a programmed reset curve in the heating unit), but that a heat pump would be unable to do the same. The boiler can modulate up and down based on the delta-T between return and supply and the target supply temp from the outdoor reset. A heat pump could do exactly the same thing (with an inverter drive, it can do it with even more granularity than a multi-stage gas valve affords).
  - dtgriscom 4y ago
    Ah, clarification: you're OK with using a proprietary (and intelligently proportional) thermostat, as long as there's a backup dry contact option if the factory thermostat fails and is irreplaceable.
    - sokoloff 4y ago
      Yes, that’s true; I’m ok to use a proprietary thermostat if I think it will save me money in 2 years max. (I’m using Sensi wifi thermostats that will become non-programmable if they stop supporting their phone app. It’s ok, as they were around $40 each after incentives and I’ll save most of that just this heating season. Its interface to the boiler is just power, common, and call-for-heat.) At least in a hydronic (air-to-water or gas-fired) application, an intelligent stat is not mandatory to get decent efficiency (from variable control). You still have building heat transfer rate and outdoor temp sensing available inside the unit even with just a contact closure.
LeonM 4y ago
> I want it to work with a contact-closure (TT/XX) input to call for heat/cooling. Sure, if you have a fancy thermostat that works better, I'm going to read the brochure, but I'm not buying it if I find out it won't work with just a dry contact input. > I want it to have an open interface to extract data (similar to the open interface of a dry-contact closure) about run-time, performance, etc. (I will, however, buy it without this.) FWIW, there is a standard called OpenTherm which most off the shelf thermostats support and HVAC systems support. It's a 2-wire serial 2-way protocol, quite simple. IIRC OpenTherm even has a fallback compatibility mode where closing the loop will enable the system at full power, though I am not sure this will work with heat pumps, as they can both heat and cool. You could even rig up a Raspberry Pi or equivalent with an OpenTherm interface and attach it to any OpenTherm compatible heater/cooler to control it and read stats.

Mvandenbergh 4y ago

Nobody will build a heat-pump system with an on/off control system like that because the performance will be awful. Certainly not an air-to-water system.

oceanplexian 4y ago
It already exists. Check out Mr. Cool Universal and Gree Flexx. Heat pumps that work with a normal thermostat exist. Most of the info about this stuff online is trash because HVAC is the most toxic online community compared to any other contracting profession. One of the reasons highly efficient mini splits haven’t took off in the USA- the self proclaimed experts want to charge $2000 to drill a hole and charge a line set, so most people DIY.
- thaeli 4y ago
  I've often wondered why this is. My best guess is that the EPA cert (not actually hard to get) has been turned into some sort of weird quasi-guild-membership thing. I can walk right in to a "to the trade" electrical or plumbing supply and they'll deal with me, no problem, no questions asked. With HVAC.. they won't even talk to you without an EPA number, even if you're not buying refrigerant. DTC for whole house systems, if they can make the regulatory side work and provide a good customer experience, is the most important part of this.
  - sokoloff 4y ago
    I'm a potential customer for DTC/DIY installation, but I think that's a pretty small slice of the market. Many of my friends are entirely willing to drop $4-5K for a single zone mini-split install (that's $1-1.5K of equipment and 2 hours of labor) and wouldn't dream of drilling a hole in the side of their house to save $3K.
    - abakker 4y ago
      I recently got quoted $17k for 2 zone mini split. I bought the tools, instructions, and watched youtube and spent $4500 total. At that savings, I don't need a warranty. I can just buy and install another system if it fails.
      - rnk 4y ago
        Can you explain a little more what you did? Just a little bit, like what brand, did you replace an existing home system. Who did the electrical, did you need duct work? I already have a forced gas system, you can just connect it up? If I only had say 4-5 rooms on one story it would be a lot easier.
        sokoloff 4y ago
        Lots of good YouTube videos and good DIY HVAC content on garagejournal.com (the latter will have good discussion on brands as well as DIY installs). For a case where you have a ducted gas furnace, you are probably better off with a traditional A coil evaporator, especially if you want invisible in the living area of the house. Those are not as DIY-friendly (but anything is DIY-able if you're skilled and bold enough, willing to learn, and willing [or eager] to buy some tools :) ).
thaeli 4y ago
As a backup option, the incumbents already make this. Carrier Infinity is a good example. Proprietary protocol (RS-485 based, so it can run over existing thermostat wiring) between the smart thermostat and the furnace, and between the furnace and outside condenser unit. Even with all these smarts, there is still a fallback mode provided with a regular old dry-contacts control wires that can hook to any standard thermostat. Yeah, the system won't operate at peak performance, but it will operate, and that's very important when every HVAC tech carries a standard thermostat with them, or even uses basic jumper wires, in an emergency until they can return with correct parts.
yencabulator 4y ago
My Carrier wall unit has a button for manual operation: > MANUAL CONTROL is intended for testing purposes and emergency operation only.
lsaferite 4y ago
Heatpumps are essentially pretty dumb devices at core. They use 24v AC for control, there's a reversing valve contactor to control if it's heating or cooling, there's a contactor for the fan, and one for each stage of the pump. Maybe there's another contactor for the emergency heating element. If you are fancy you might have contactors for UV sterilization, humidification, and/or dehumidification. Literally the 'smartest' part of my HVAC system, beyond the thermostat, is the blower fan. It's a variable speed motor and has a speed controller integrated into the motor housing with multiple 'taps' that let you control the fan speed in steps. It's configurable if you have the programming hardware.

RetpolineDrama 4y ago

>but I'm not buying it if I find out it won't work with a dry contact input. But... why?

sokoloff 4y ago
Because it's from a new entrant to the market and I don't know that their complex interface will be available, supported, and serviceable 12 years into the 20 year lifetime of the equipment. I do know that I will always be able to provide a dry contact closure in the event they go belly-up and the thermostat goes unsupported. I have my current gas boiler working via an outdoor reset mechanism that provides flow water at 116°F to 135°F via a dry contact closure from the zone relay box. There's no reason for me to believe that Bosch (and others) can create a modulating boiler that works efficiently from just a dry contact closure input from the house (plus a flow temp sensor, a return temp sensor, an outdoor temp sensor, and a programmed reset curve in the heating unit), but that a heat pump would be unable to do the same. The boiler can modulate up and down based on the delta-T between return and supply and the target supply temp from the outdoor reset. A heat pump could do exactly the same thing (with an inverter drive, it can do it with even more granularity than a multi-stage gas valve affords).
- dtgriscom 4y ago
  Ah, clarification: you're OK with using a proprietary (and intelligently proportional) thermostat, as long as there's a backup dry contact option if the factory thermostat fails and is irreplaceable.
  - sokoloff 4y ago
    Yes, that’s true; I’m ok to use a proprietary thermostat if I think it will save me money in 2 years max. (I’m using Sensi wifi thermostats that will become non-programmable if they stop supporting their phone app. It’s ok, as they were around $40 each after incentives and I’ll save most of that just this heating season. Its interface to the boiler is just power, common, and call-for-heat.) At least in a hydronic (air-to-water or gas-fired) application, an intelligent stat is not mandatory to get decent efficiency (from variable control). You still have building heat transfer rate and outdoor temp sensing available inside the unit even with just a contact closure.

LeonM 4y ago

> I want it to work with a contact-closure (TT/XX) input to call for heat/cooling. Sure, if you have a fancy thermostat that works better, I'm going to read the brochure, but I'm not buying it if I find out it won't work with just a dry contact input. > I want it to have an open interface to extract data (similar to the open interface of a dry-contact closure) about run-time, performance, etc. (I will, however, buy it without this.) FWIW, there is a standard called OpenTherm which most off the shelf thermostats support and HVAC systems support. It's a 2-wire serial 2-way protocol, quite simple. IIRC OpenTherm even has a fallback compatibility mode where closing the loop will enable the system at full power, though I am not sure this will work with heat pumps, as they can both heat and cool. You could even rig up a Raspberry Pi or equivalent with an OpenTherm interface and attach it to any OpenTherm compatible heater/cooler to control it and read stats.