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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.