Heating and cooling different zones at same time with boiler and heat pump

mburg · May 3

I am working on a project with 3 geothermal heat pumps connected to 21 zones of radiant heat and 6 hot/chilled water air handlers.

The issue we are trying to resolve is particularly in shoulder season the house tends to overheat. the homeowner want the warm board running, but certain zones overheat and require cooling. they also like to run the fireplaces which isn't helping with this issue either. The system requires manually switching heat pumps back and forth between heating and cooling mode to manage this.

I am working on deciding what the best way to resolve this is. I want to keep things as simple and reliable as possible even if there is a slightly higher energy cost.

There is a Crestron system and I'm told they can make thermostats auto switchover.

Me and the geo company are thinking its best to have entire geo system run on either heat or cool. When both heating and cooling is required the geo will be providing cooling and utilize boiler for supplemental heat. Unsure of how to manage geo operating mode at this point.

I included a drawing showing my thoughts on piping.

As far as controls: Put sensor in heat pump buffer tank connected to tekmar 150 control. The 21 radiant zones will have separate zone valve controllers than the fan coils. If any radiant zone calls the end switch for those zones will close powering demand on tekmar 150. If geo buffer tank is bellow required radiant heating supply temperature 3 and 4 will close on 150 sending power to 3 way ball valves to switch flow direction for boiler. After valves switch end switch on actuator will act as demand to boilers?

Couple questions:

1- I was thinking having two separate three way ball valves was the best approach to completely isolate the geo from boilers. maybe two is unnecessary and there's a simpler approach. Having two separate 3 way valves would require expansion tanks on both boiler and geo side of system. I don't think there is a issue with this since they will be isolated from each other.

2- I have never used Belimo valves before. I was thinking of using them for all 27 zone valves and the (2) 2" three way ball valves. Are they as high quality and reliable as I'm led to believe?

appreciate any thought or different perspectives on this!

Thanks,

Matt

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EBEBRATT-Ed · May 3

You have a two pipe system so you can only heat OR cool. Not both.

A 3 pipe can cool or heat but is inefficient and wastes energy.

Commercial building uses a 4 pipe system (two pipes heat and two pipes cool). You talking major re piping and automatic valve and controls to do what you want. No very practical

EdTheHeaterMan · May 3

As Ed said you have a 2 pipe system so Heat or Cool, not both. However there is a somewhat easy fix since you have two systems for heating.

Adding some pipes in order to isolate the radiant floor zones from the AHU zones may partially solve your problem. With the following diagram you can heat the floors and cool the rooms at the same time.

Screenshot 2026-05-03 at 10.01.59 AM.png

See how the A, B, AB valves are configures so the AB is feeding the radiant floor zones while yopu can select from eitheer the heat pump (A) during the heating season then switch to (B) boiler when the weather gets too cols for the AHU to provice sufficient heat at design temperatures, the 3 way motorized mix vlave will provide low temperature water to the radiant floor zones at that time.

In the cooling season, when your client (they must be to wealthy to be called customer). desires cooling for the air temperature but still wants warm feet, the valves can be set up to send chilled water to the AHU and heated boiler water to the floors.

So It is not just a wiring/control problem. It is a pipe design problem.

hot_rod · May 3

Maybe a 4 pipe system if you want heat and cooling at the same time. Systems like this are used in mountain homes with large south facing glass. Cooling on in the southern rooms, heat on for north rooms.

Idronics 28 has some ideas. It doesn't need to be this elaborate, the concept of 4 pipe is the idea.

https://www.caleffi.com/sites/default/files/media/external-file/Idronics_28_NA_Contemporary%20hydronic%20cooling%20for%20commercial%20buildings.pdf

Screenshot 2026-05-03 at 10.18.33 AM.png

EBEBRATT-Ed · May 3

Best system I know of to heat and cool at the same time is a boiler/water tower system with heat pumps.

I worked on several schools and office buildings that had those systems in the 80s and 90s and they worked well.

The heat pumps take heat from the water loop in heating and reject heat to the loop a in cooling. The water loop is maintained at 80 degrees either by the boiler adding heat or the cooling tower rejecting heat.

They also had perimeter HW baseboard for the colder winter months which they had a separate boiler for. But it could all be done with one boiler as well and the radiant floor would take the place of the baseboard.

hot_rod · 1:52AM

https://forum.heatinghelp.com/discussion/comment/1895679#Comment_1895679

Those heat reclaim systems are still designed for the right applications. Belimo makes 6 port diverter valves for that use.

Heating and cooling different zones at same time with boiler and heat pump

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