What's a TON got to do with AC?

So you've probably heard of someone refer to an air conditioner's size in terms of  "TONS".  Something like "I got a new 4 TON HVAC unit".  This refers, not to physical size, but to the capacity (ability) of the equipment to generate heat.  That's right, even air conditioning (cooling), is sized by it's ability to produce heat.  In the case of air conditioning, the heat is being "pulled" from inside the house and dispersed outside.  This is why there is always an outdoor component (the air conditioning compressor) when you have AC.

Back to TONs... most people thing of a TON as being 2000 lbs. but with regard to HVAC, a TON is a measurement of heat generation per day.

1 TON of air conditioning is a measure equivalent to the amount of heat necessary to melt 2000 lbs of ice (H20) in a 24 hour period.

But how did we get there? A BTU (British Thermal Unit) is the unit we use express heat energy.  One BTU is equivalent to the amount of heat energy released when burning 1 match all the way. When rating an HVAC unit either for heating or cooling, the amount of BTUs per Hour is often sited.  It has been measured that it takes 143 BTUs to melt 1 lb of ice.  Since, 1 TON of ice is 2000lbs, It will take 2000 x 143 = 286,000 BTUs to melt 1 TON of ice.  The ice could be melted by lighting 286,000 matches all at once or by lighting one at a time... In other words, BTUs only tells us how much heat energy is necessary but not over what time period.  It could melt in 1 minute, 1 hour, or even 1 year depending on how the energy is generated.  So, to rate the output of HVAC equipment, someone decided back in the early 1900s (probably someone at Carrier) that it should be done over a 24 HR peroid (1 day).  This is how we get 286,000 BTUs / 24 hrs =~ 11,917 BTUs per hour or commonly know as 12K BTU/hr is equal to 1 TON.

This means that that 4 TON AC unit you have can melt 8,000 lbs of ICE per day or about the same size block of ice as a Suburban.  That's a lot of heat energy!

De-humidification and SmartZone - Zone 1 Thermostat Control

Although SmartZone does not have any built-in capabilities for controlling DE-humidification (DH) or Humidification, some applications are possible by using a thermostat on ZONE 1 that does have the capability to control DH.

“DE-humidification, in most residential systems, is simply running the equipment in COOLING with LOW speed fan instead of HI speed fan.”

Before we get to zoning, the equipment being used must have the capability to control humidity.  This usually means it has a terminal (DH/BK/DS) that is energized or DE-energized by a thermostat to control fan speed of the equipment.  Controlling fan speed allows the equipment to DE-humidify the air when the fan is running in low speed.

Back to zoning, using zone 1 thermostat to control DH is not as simple as wiring directly from the thermostat to the equipment.  PLEASE DO NOT DO THIS.  The equipment and the zone thermostats are running on different transformers and this will case problems and potentially damage to some components.  You could isolate the output from the thermostat with a relay to get around this issue of different transformers but you would still have an issue with this method of wiring "around" the zone controller.  The issue can arise when zone 1 calls for DH but the equipment is already running in heat, this mixed signal might just be ignored by the equipment but we cannot take that for granted... all equipment works differently.

The best way to control DH using SmartZone on single stage equipment is by using the method below.  It may seem a little UN-orthidoxed but it is a valid APP note from the engineer at Ecojay (It's intended to work this way).

1. Select a DH enabled thermostat of your choice
2. Connect Y2/ECO on SmartZone Zone 1 to Zone 1 Thermostat DH/DS/BK
3. Connect Y2 on SmartZone Equipment toEquipment DH/DS/BK
4. Set Zone 1 "STAT TYPE" to G2
5. Set DIP switch #4 to "LOCKOUT"

Zone 1 thermostat will now enable and disable DE-humidification any time the equipment is running in the cooling mode.
NOTE: When starting cooling from OFF state, 90 second delay will occur before HIGH speed fan will energize.

Using this method we are assuming that the equipment is expecting DS/BK/DH input terminal to be ENERGIZED for high speed fan and DE-ENERGIZED for low speed fan.  This method should not be used for more than 3 zones or with multi-stage compressor equipment.

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More unbiased Zone control discusson on homeenergy

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QUESSTION by Adam Zielinski

Homeowners with forced air duct systems always want to close the registers in rooms they aren't using, and close the doors to those rooms, in the belief that doing so will save energy and money.
I always thought doing this was over-rated and unlikely to save a significant amount of energy or money.  I could see doing it for one or two rooms perhaps, but sometimes homeowners close off half of their house or more.
This creates unbalanced air flow in the duct system and likely results in over heating the furnace heat exchanger, and or short cycling the furnace.  So the furnace spends a lot of time in start up mode and less time at peak efficiency.
I have not seen any real studies done on this however.  I'd like to see some data or research on this.

Reply by dale conner
Adam, most furnaces will move the proper amount of air through the blower and heat exchanger if the furnace cabinet pressure doesnt exceed .5 IWC and the furnace capacity was chosen based on a manual J calculation. This information can be found in the furnace installation manual or IOM (installation,operation,maintenance) that comes with a new furnace. However, this does not mean we are getting adequate air delivery to all of the rooms in the house due to excessive air leakage in the ducts and/or incorrect duct lengths or diameters routed to each room.

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QUESTION by Judi Lyall

How about using a motorized damper ?

Reply by dale conner
A single motorized damper can be used to control a zoned area but you also have to install a barometric by-pass damper to prevent over pressurization www.zoningsupply.com

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See full discussion: http://homeenergypros.lbl.gov/group/hvac/forum/topic/show?id=6069565%3ATopic%3A7207

Honest discussion on homeenergypros about zoning advantages.

Are Zoned Heating/Cooling Systems a Good or Bad Idea?

Excerpt from homeenergypros discussion about HVAC Zone controls.

QUESTION by Jon LaMonte

For starters, I live in Atlanta, Ga and I am not an HVAC pro so this is a serious question that I would like answered for one of my clients.  I understand the premise of a zoned system and on the surface, it sounds like a good idea. Then I considered the fact that I have always told my customers that it is a bad idea to close off vents in rooms they are not in because of duct leakage.  Also, the second law of thermodynamics simply states the hot goes to cold, so now the unheated areas are doing their best to rob warm air from the heated areas.  Finally, if your zoning a single system, aren't you creating on oversizing issue because the unit (that was probably oversized in the first place) is now servicing a smaller area than what it was designed for?

View fullsize

Reply1 by Chris Heenan

Zoning has benefits beyond temp control. Most often the home does not require the full 2 stage heat or cooling as the system only needs to satisfy a portion of the home. So, then if 1/2 the heated air goes through a properly sized and balance bypass, the return air (from home) will mix with warm supply (from bypass) before going thru the system again. You may not need to go beyond 1stage heat (or cool) except in extremes. This is most beneficial in raising supply temps from heat pumps when in winter mode. Most supply vents feel 'cool' to homeowner. Not so when zoned and not call on all zones.

Flip it to cool, and the bypass send dehumidified cooler air across the coil. Decreasing high side pressures and amp draw of compressor. Then the air gets more heat extracted and further dehumidified. Pulling out additional condensate and running less. Remember systems have to be careful not to oversize as dehumidification is crucial to comfort. Dry and cool temps out supply vent. Not too shabby.

Reply2 by dale conner

Zone sytems are rarely installed properly but can be efficient if properly designed. The goal is to be able to set back the temperature a few degrees in a zone that isnt being utilized while keeping another zone comfortable that is being utilized.  A single unit with a zone system will have a by-pass duct sytem to dump the air thats been cut off from one zone back into the duct system to be used in the zone that is being used.

*Reply3 by James Jackson on

Have you ever been driving down the interstate hwy and come up on an exit ramp that has traffic backed up? As the traffic backs up and eventually fills the exit with cars you end up with a slight back up on the entire highway. this is the closest scenario i have been able to come up to help people understand why closing doors and vents is a bad idea. if you have a run off of a main trunk and you close the outlet or register you will cause the air to back up into the trunk causing turbulence in the trunk line resulting in a decrease in air flow in other areas on the system. this can also cause multiple other problems like pulsing and excessive noise from the increase in pressure.

another thing to remember when you shut doors in a home with no return air you cause a difference in pressure in the home. The room you have closed is now significantly positively pressurized and the house is now under a negative pressure. This why some homes have the doors undercut by 3-4 inches trying to allow the air to get back to the return.

Ok as far as the zone system goes... There is so much more thought involved in properly setting up a quality zone system that i see very few done correctly. If you want to do one correctly you first need to make sure you are using a multi-stage HVAC unit so the unit can run on low speed if it is only conditioning one zone. A bypass or crossover duct with a barometric damper is needed if you are conditioning a small zone and the air handler is still supplying too much air, but if you are going the zone route don’t use contractor grade units and piece it together with a simple zone controller. Get a high efficiency v speed unit that is designed for this application.

But what happens when you change the temps in a zone in the house 4-5 degrees?? Energy moves from hot to cold so you end up indirectly heating or cooling the entire space regardless. This brings us to another scenario. The return air in the zone that is off. My experience with working on correcting issues with homes using zone systems has been the returns are never dampered so if the zone is completely shut off you have just installed a permanent blower door. if the zone is off one you are returning hotter or colder air to the system and two you are causing that zone to have a negative pressure.

Just some things to think about !!

Learn more at www.zoningsupply.com

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BETTER with Zoning done right!

Single thermostat can have issues

My editorial conclusion:
Zoning CAN be effective if and ONLY if it's designed and installed properly.  This means ducts, dampers, equipment size (tons).  It also means the right zone panel setup with energy saving features like SmartZone.  Finally, to make zoning work best and comfort control and energy savings, the home owner must properly control the thermostats.  Zoning isn't a "set-it-and-forget-it" system, it must be managed to be effective.  More articles about zoning

See full discussion: http://homeenergypros.lbl.gov/group/hvac/forum/topic/show?id=6069565%3ATopic%3A7207

Retro thermostat... 1982 Electronics Guide review of Magic-Stat

Published in Playboy's Electronic Entertainment guide in Fall 1982. 

This is off of our normal subject but I came across this old magazine that includes other articles like "There's more to life than Pac-Man: How to beat Donkey Kong" and "What computers can do for you" which says that "VisiCalc is the most popular program of all time with 250,000 copies sold".  And it included a scathing review of this Magic-Stat product.  Sold for $79 mail order.  At first glance, I thought it was just another ugly thermostats in a long history that still goes on today.  Then i read the article which explains a "LEARN" mode that makes it easier to set much like the nest would do decades later.  Also, it claims to have what is now reffered to as "adaptive recovery".  This is where the thermostat starts the equipment before the set time so it can get the home to temperature at a specified time instead of just starting to get to temperature at the time of setpoint.  I haven't done any fact-checking, but it says they are the first thermostat to do this... too bad it took 20 years for this to become a more standard feature.

Here are a few more pics I took of the magazine...i claim no rights or ownership of any of this material.