Hello Gene,
Yes to everything in your post except that I mostly work with residential building. My specialty is hydronics and radiant panels. We manufacture extruded heat transfer plates that we use to create radiant panels including radiant floors and now ceilings. We were getting more interest in radiant ceiling cooling so we created a insulated panel product that accepts one of our extrusions which in turn accept PEX tubing. We can create radiant ceilings using products and methods similar to what we are used to using in radiant floors.
I’ve sold ERV’s for years. The DOAS ideas that are prevalent in commercial construction I learned from Robert Bean. With the ATW heat pump we have a way of providing both de-humidification and sensible panel cooling with a hydronic distribution system. One of the reasons I am lurking on Allison’s excellent website is learn more about moisture handling and other kinds of heat pumps. I think that hydronic distribution and ocontrol the doas / ATW / hydronic radiant panel cooling offer very useful features that address a lot of issues with air to air heat pump systems. These issues are well represented in this thread.
We are hoping to see Viessmann’s propane based ATW monobloc system sooner rather than later. Yes, they claim it can produce ~160°f water and propane only has a GWP of 3. I think that propane is a doable refrigerant where CO2 is problematic at best. Viessmann’s existing condensing gas boilers are capable of a 20% hydrogen mix. They have plans to increase this to 100% as they Germany’s hydrogen plan established. This is also a fuel that can be solar/wind produced, stored and used in existing infrastructure. Viessmann being Viessmann they also offer fuel cells off the shelf. We do hope to get their ATW heat pumps soon. Thanks for your interest and thanks to Allison for the forum.

Also, why isn’t VRF being offered in the residential market?

Hi Dale, It sounds like you are working on commercial buildings with DOAS systems with energy recovery and chilled beams and radiant ceilings. I used to do that when I was working as a consulting engineer. It was the system that was more efficient than VAV systems we had been using and provided better ventilation. It’s interesting how residential systems in very low energy houses seem to be following a similar path: Air tight with ERVs and radiant floors or wall mounted fan coils for cooling and dehumidifying. I don’t hear of many homes using passive Valence heating and cooling distribution (Edwards Engineering), but it could happen. Not many folks are adding heating/cooling coils to their ERVs, but that would be easy with an air-to-water heat pump. I read that Mitsubishi is also selling a high-temperature ATW heat pump now in Europe, using Propane for the refrigerant. We need that in New England for all the older homes with hot water heat. The Air-to-Water heat pump is ideal for this, but also for new homes with low-temperature heat/cool terminals. 1. They are easier to maintain (remove outdoor unit and do the work in a warm shop), and 2. they have a backup resistance heater in the indoor buffer tank to keep warm if the heat pump fails. 3. Like all hydronic systems, they are easy to monitor with a temperature and pressure gauge. 4. Refrigerant volume is smaller and less likely to leak with no field-made joints. 5. From what I have seen, very-low GWP refrigerants are coming (propane and CO2) in order to reach the higher temperature needed in old homes. That’s good for the planet. 6. Since all the refrigerant is outdoors, they can safely use low GWP flammable refrigerants like propane. 7. The coming high temperature hydronic models that could replace a boiler and use the existing distribution system (plus a few AHUs for cooling), might lower the installed cost enough to drive wider adoption. 8. In addition, with a higher water temperature available, they can recover from substantial night setbacks in a short time and then revert to a lower temperature to maintain comfort with higher efficiency. The mini-splits can’t do that because the supply temperature is too low, and so their remote controls don’t include the setback feature. But setback is a way to reduce the total amount of energy you have to provide on an annual basis, so giving that up with a mini-split means you have to pay for more energy each year. 9. Heat pumps and AC systems have an expected life of about 15 years. When your Multi-split heat pump fails after 15 years, I don’t think any contractor will want to replace just the outdoor unit and reuse the indoor system. It becomes junk. With ATW heat pumps all of the indoor distribution and storage tanks are generic and completely reusable. You would just replace the outdoor unit as you would if your boiler failed. The rest of the system can be reused, saving money on initial installation and replacements. 10. Your plumber can install them just like a hot water boiler, so the shortage of refrigeration technicians would not hinder nationwide home electrification. The more I learn about Air-to-Water heat pumps, them more I think they are the ideal system for new and old homes. New ones would use low temperature heat distribution, but the coming high temperature models will work on older homes with baseboard or radiator heat.

Hello Gene,

You describe some of the advantages of using hydronics to create durable heating and cooling distribution systems. Yes, air to water heat pumps only see the buffer tank, the hydronic distribution system takes it from there to serve a variety of heat exchanger types, central air, fan coils, radiant panels etc.
The hot lash up is to use a Dedicated Outdoor Air System for Ventilation and De-humidification (DAOS) and then use relatively high temperature (66°f) radiant panels to absorb the sensible gains.
The de-humidification coil can be operated with chilled water from the air to water heat pump (38°f) to drop the moisture out of incoming ventilation air. Typically this drier air is then introduced to an ERV for fresh air distribution.

We are producing a new product here – insulation panels that fit our ThermoFin heat transfer plate – the system allows designers and installers to create practical radiant ceiling systems that can be used for heating or cooling.

Dale, I know you like hydronic systems and I do too. This brings up still another advantage of Air-to-Water heat pumps. Heat pumps and AC systems have an expected life of about 15 years. When your Multi-split heat pump fails after 15 years, I don’t think any contractor will want to replace just the outdoor unit and reuse the indoor system. It becomes junk. But with an ATW heat pump, the refrigeration system is a discrete outdoor unit that can be easily replaced, while the indoor hydronic system has a much longer life that can outlast 2 or 3 or more outdoor units. Replacing a failed ATW outdoor heat pump unit is a simple process, so I don’t think the recommendation to use single zone heat pumps applies. There is also a backup resistance heater in the indoor buffer tank, so there should never be a loss of heating even it a new heat pump is not available immediately. In effect the ATW heat pump IS a single zone system. Its job is just to heat a tank of hot water.

You oiled fired hot water system is not the same animal as an air to water heat pump driving several independent zones of radiant floors. You don’t have to handle air to use heat pumps which are happier with the water backed heat exchanger and low temperature distribution system.

The economies of scale have it that as soon as you rack up several units in parallel then the pressure is on to make each one cheap so as to make the whole system affordable. It is possible with the system I described above to set up central high quality source equipment that serves distributed, automatically controlled heating zones.

I had issues with my oil heated hydronic system multiple times. Everything fails eventually

Yeah I have one mini split one to one unit which does most of my cooling and heating. Especially in the winter I usually run that unit and leave the bedroom doors open more often than not. I kind of wish my bedrooms were set up that way but what are you going to do. Seeing that it’s my only heating source now that I got rid of oil I do need a unit in each room if it gets real cold so then I would have four outside units which would be a bit much.

John Gwinn,
Well, the redundancy argument has it’s adherents. With my hydronic systems I beg to disagree. However, with refrigerant systems, I would agree with your “AC guy” – though the attitude speaks to the how reliable he thinks the equipment is. Much of this mechanical stuff seems pretty cheesy, i.e. not well built.