Is there any way to differentially cool one room vs. others?
I’m trying to figure out the mechanical design for a new home build. Plan is to use ducted air-source heat pumps as the primary heating/cooling.
Right now the plan for the heat pumps is to use one per floor of the house (3 ~1 Ton units in total: basement, main floor and upper level).
The bedrooms are mainly on the upper floor, and I’d like to get to more granular, room-by-room zoning up there — and in particular, I want to be able to differentially cool certain rooms to be 2-5 degrees F cooler than other ones
If the problem statement were that I need to be able to differentially heat certain rooms, I’d just throw an extra electric radiator into a couple of the bedrooms and be done with it. But is there any way to achieve differential cooling? I don’t want to have to cool the entire house/floor down to these levels if I can avoid it. And if I try to install more heat pumps, I’m going to end up with oversized equipment and short cycling.
Any suggestions on options to consider?
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> The bedrooms are mainly on the upper floor, and I’d like to get to more granular, room-by-room zoning up there — and in particular, I want to be able to differentially cool certain rooms to be 2-5 degrees F cooler than other ones
Is it just for personal preference, or are you trying to let unused rooms stay warmer?
Preference. Some hot sleepers in the house, but if we kept the whole house at 65 degrees the rest of us would be freezing and our energy bill would be much higher than needed.
In theory I could cool the house to 65 everywhere and then heat up the other rooms with space heaters, but that seems so laughably inefficient that I feel embarrassed even suggesting something like that on a site called *Green* Building Advisor!
Ceiling fans.
You could put the heat pump head in the room you want the coldest, then use fans in transfer vents to the other rooms, with those fans controlled by thermostats in the other rooms. In this way, the heat pump directly controls the temperature in the chosen room that will be kept coldest, and the other rooms will only receive cold air forcefully when their thermostats call for it. This isn't a perfect system, but it would be relatively inexpensive and easy to implement.
If you want anything fancier, your best option is probably a ducted system with controllable dampers in some of the rooms to allow you to zone the system. This is going to be much more complex and costly to install though.
Bill
Interesting idea. So in this case the thermostats in the secondary rooms are only controlling fan speed and nothing else?
The flip side of this in the winter months though would be that the main room would be the one getting the majority of the heat and then some portion of this would be siphoned off to the other rooms? That might not work out as well. (my original plan in the winter for differential cooling was just to open windows for a few minutes per night in the rooms that need to be cooler)
I think I'm talking myself into the zone damper idea...
You could install a VRF heat pump system, with individual cassettes in each room... but more $$$. Many options to choose from.
My (very limited) understanding of VRFs is that they're large and expensive.
You've confirmed the expensive part in your comment. But if my total load for the house is on the order of 3 tons, does a VRF make any sense? How low can any individual cassette go (and for aesthetic reasons, it's critical I use hidden cassettes/ducted air handlers)
I had just dismissed VRFs out of hand from the get-go, but maybe it's worth revisiting...
Not cheap but it sound like what you want, you can look at Airzone:
https://www.fujitsugeneral.com/us/residential/benefits/airzone.html
Other option is to install dampers on each branch driven by a local thermostat. In this case you want to over-provision each room but adjust the closed position of the damper to still allow some flow to avoid restricting the air handlers.
Pretty simple and requires no fancy controls but there are limits as you are still relying on the main unit thermostat to set the amount of overall cooling/heating.
This is interesting. My MEP designer works primarily with Mitsubishi and said Mitsubishi no longer supports AirZone if I also want back-up heat strips on my air handlers (which I think I do for the occasional week-long cold snap down below -25 that happens in the winter months in my region).
Maybe AirZone plays better w/ Fujitsu products? Worth looking into.
What you're talking about is zoning.
Poor man's zoning is to have a ducted system with dampers on each room, you fiddle around with the dampers and system thermostat to see if there's a setting that gives the mix of temperatures you want. From there you can move up to automated dampers with thermostats. The challenge is always configuring it so that you don't choke the air off too much.