HVAC Battles

In the Northeast we’re at the time of year when heating and cooling systems can start to battle one another if mis-configured.

This is a personal favorite of mine … there’s nothing like saving energy by realizing you were doing worse than throwing it out the window: HVAC battles are hard to beat as an energy conservation target.

A classic find is having a building boiler running on overdrive while apartments are running AC to cool down. This is perhaps an NYC special case due to the ubiquity of overzealous steam heat (“open that window!”) but it can be replicated on a small scale by having electric radiant floor heating on through Summer. It happens!

So I’m wondering if anybody has multiple heating/cooling sources that could be establishing battles. Any Pros out there with fun stories?

And while were at it, there are also cooling-cooling & heating-heating battles. Zones! Spouses! Kids!

Here’s one I’m looking at, this is now (and it’s been pretty warm out).
This is a multi-story building steam boiler that’s not doing hot water heating.
The super has shoved a large fan in the boiler room to keep the temperature down!

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We have a complex battle here here in our household, even after sorting out the floor heater thermostat programming, and even after sorting out whose comfort level we’re aiming for (my wife’s of course). The real battle in our house now, as the cooling season gets into full swing, is between outside weather, thermal mass, allergies and configurability of thermostats. Summer weather means lots of sun, warm (70-80+ degree) daytimes with cool (50 degree) nights, with mild to low humidity. The goal is to walk the fine line between heating and cooling on multiple systems to keep the right rooms within the 68-72 degree comfort zone.

The constraints:

  • Allergies mean that for much of the year, we can’t open windows to mange the temperature.
  • Stucco exterior means the outside of the house heats up to well above the ambient temperature, and due to the thermal mass, keeps radiating heat for hours after sunset.
  • Stone floors downstairs, with underfloor heating zoned to various living spaces. Once again lots of thermal mass that generally stays cool unless heated.

The control tools:

  • Two Ecobee thermostats, upstairs and downstairs to control the forced air HVAC systems with separate natural gas furnaces and AC compressors
  • 10 auxiliary Ecobee room sensors to watch temperatures in individual rooms beyond the hallways where the two thermostats reside
  • 10 Keen smart vents in the upstairs rooms to fine-tune HVAC airflow. Keen and Ecobee have an integration that allows Keen to use the Ecobee temp sensor and adjust the vents based on temperature goal for that room and occupancy.
  • 4 NuHeat/Signature thermostats for the different floor zones. They have both in floor temp sensors and air temp sensors, but each thermostat can only use one sensor for programing at a time, and really only programmable for simple daily schedules with a common Away.

Prior to the new floors and floor heating last summer, I had a good setup going with just the Ecobees and Keen, but adding floor heating has caused new problem and opened up new possibilities. My family loves the floors heated in the AM, but due to the thermal mass that brings the possibility of a warm floors (even if off), fighting with the cooling system on days when the house

Right now, my biggest challenge is figuring out how to program the the floor heat more intelligently so I can take advantage of the floors’ thermal mass. On days when it’s going to stay cool well into the afternoon, I would like to use the floor heating as the the main heating in the AM, but on days when it is going to get warmer than the comfort zone by mid-morning, I would rather leave the floor heating off and use the floor to keep the house cool. Still working on the instrumentation / access to make that work. The Nuheat/Signature has an accessible API, like Ecobee, and the thermostat actually has access to the predicted temperature for my location, but just doesn’t allow that as part of the programming. Hmmmm.

Here’s a summary of the downstairs usage from the Beestat app (just Ecobee data, no NuHeat).

Below is a badly chosen floor heating program for hot day (Family Room)

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Nice details as usual!

On a much smaller scale my Nuheat (single zone) in the kitchen is a relatively huge thermal mass: more than a third of the apartment square footage. It’s the primary heat source in the entire place. Adjusting it seems to be most effective when done manually and tweaking the programmed set points. Thinking about the reasons why that is:

  • We bake quite a lot and use the (gas) oven.
  • The kitchen has a seriously efficient hood exhaust that can close the kitchen door if cranked to high.
  • When we do laundry with an unvented electric (evaporative) dryer the bathroom fan stays on and vents the humidity … and draws in, in an uncontrolled fashion, outside air.

How is your outside air intake? Seems like if you had a substantial HRV/ERV with HEPA/plasma filtration you could use the cooler overnights + thermal mass to cheat some watts/BTUs. In winter I like to sleep in a cold room like a Finnish baby and in general I find that people don’t realize how nice it is to open windows or suck the heat out of a bedroom. This has distinct disadvantages when you’re trying to heat your space during the day! In warmer or transitional seasons though this is advantageous. Zoned HVAC with the ability to heat and cool at the same time is ideal: you can use room air and thermal masses as batteries.

I have an iQAir HealthPro w/carbon filters that has 6 CFMs between 40 & 240. I just got the duct kit that will allow me to finally interface it to the outside (i.e. on the intake side). I’m pretending this is a “spring energy saving project” but it’s probably more about dust avoidance and it remains to be seen whether it will save any watts. Sense will definitely help to quantify things. My 5,500-ish cubic foot space is going to be running on positive pressure. Working out a practical method for HRV/ERV is one of those non-trivial tasks that means it may never happen. I wish there was a small HEPA ERV on the market that checked all my boxes.

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