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I am having this same debate with myself. I have an AWHP system that currently services a portion of my house, with the eventual goal to expand the system to cover my whole house. I currently have the entire system filled with glycol. While this has worked OK for the last couple years, I am considering installing a heat exchanger and switching the indoor portion to water for the following reasons:

• I have had one leaky fitting on a fan coil in a bedroom. Thankfully it was minor, I caught it quickly, and the bedroom floor is vinyl so nothing was damaged. But its a lot easier to clean up water than glycol if a leak occurs. A catastrophic failure would result in not only a mess to clean but also require purchasing more expensive glycol
• I don't want to deal with draining and storing up to 100 gallons of glycol if/when I need to add or replace a component
• One of my fan coil emitters is pretty undersized, the reduced heat transfer of glycol is not helping this situation, especially in cooling season when the glycol becomes more difficult to pump due to low temp and I'm losing both flow rate and heat transfer

I'm not a professional, just a guy who has been living with this for a few years and wants to make my life as simple as possible to add, repair, or replace components as needed. My understanding is that if the heat exchanger between the inside and outside loops is sufficiently sized the efficiency loss in the exchanger will not be much different than the efficiency loss of using glycol throughout the whole system

glycol flows better than water so will leak more readily. Glycol needs to be maintained or it will become corrosive and damage system components.

Hello,

I'm looking at options for air to water heat pump systems. This would be for space heat and DHW using a reverse indirect buffer tank.

Some manufacturers system designs call for the AWHP to directly heat the buffer tank, with the entire tank and hydronic zone loops being glycol mix. Other manufacturers (US Boiler) suggest a plate exchanger between the AWHP and the buffer tank, with glycol only in the outdoor heat pump loop.

If I understand, the pros for the exchanger are:

• Less glycol. A buffer tank worth of glycol mix isn't cheap, and if you need to drain the system, you would need to deal with all of that mix.
• Better heat transfer / easier pumping in the hydronic zones and indirect tank without glycol.

Cons:

• More parts: heat exchanger, additional circulator, valves, etc. Probably eat up the cost of glycol savings.
• Loss of efficiency through the exchanger, critical to get flow rates / Delta T correct.

Thoughts?

Thank you.