Multizone Systems: The Single Flow Problem

Over the past several posts, we’ve been hitting on the big deal with multi-zone HVAC Systems. You can attain amazing levels of control over how hot or cold any given room is. That is, except for one problem: you can only really push one “direction” at a time without making things incredibly complex.   One Temperature Change Suppose most of your building is set around sixty eight degrees. Maybe one room wants seventy four and another sixty. The temperature outside is a warm but not unbearable eighty seven degrees. Our multi-zone system kicks in and sends exactly the right amount of cold air to exactly the right rooms as needed to achieve those desired temperatures. All sounds good, right? What if someone wanted their room to be ninety eight degrees? Maybe they’re curing concrete or they’re homesick for some equatorial inferno. This shouldn’t be a problem for our amazing system, right? Just raise the thermostat and hot air will come pouring into the room? We’ve been presenting the most straight forward, affordable, and common multi-zone system: one set of ducts, and one set of pipes. In order to heat that one room above the outdoor ambient temperature, the furnace and cooling system would be running at the same time. They would both be pushing hot or cold material into the building’s one distribution system. The air or water would mix and become the median temperature, something neither hot nor cold […]

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Multizone HVAC: The Ductless System

Multizone systems can be big, complicated, and a challenge to cram into small spaces. If you’re using hot and cold water for your heating and cooling, you need to install valves and actuators everywhere, possibly install a whole second set of pipes for a “dual pipe” system that meets any need, and make sure you can pump enough water to satisfy the beast. In forced air applications, you would have to tear apart your ducts to add the controls and fans, then spend ages locating and sealing every leaking part. This nets you a working system, but it could be better and easier.   The Central Problem We tend to centralize our HVAC hardware as much as possible. You do all your heating and cooling in one place, then send the air or water around the building. It makes a lot of sense. You only need one or two boilers for most places, even industrial settings. Put it all in one place and save on energy costs and complexity, except when you want granular control. With a central heat or cooling source, you need to add tons of controls to manage the flow hot and cold air. You’ll lose a lot of energy by sending air and water around too. Leaks in air ducts and pipes radiating heat into the open air pose annoying losses in efficiency. There’s only so much you can do to fight nature’s hell-bent desire to […]

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