Healthy Work Environment Design Ideas Help Employers, Employees and the Environment!
Showers at work??? Creating a “lounge feeling” in the business place???
Showers at work??? Creating a “lounge feeling” in the business place???
A Solar Energy incentive program (Made in Minnesota Solar Incentive Program) for both residential and commercial buildings recently came to our attention. Upon being asked our opinion of the program, a lively discussion ensued in the offices of APPRO and CERRON surrounding the use of environmentally friendly materials and sustainable energy resources.
Originally posted on May 29 2013 by Allison A. Bailes III, PhD, GBA Advisor on the Green Building Adviser Website at: http://www.greenbuildingadvisor.com/blogs/dept/building-science/why-do-we-measure-air-conditioner-capacity-tons
When we talk about “tons” of air conditioner capacity, the expression refers to the weight of a quantity of ice that would provide the equivalent amount of cooling. Before modern air conditioning, buildings were cooled with ice harvested from frozen lakes.
A few years ago, a HERS rater student in a class I taught told a funny story. He was an HVAC contractor and said he was installing a new air conditioner for an elderly woman. As he was explaining things to her, he mentioned that they would be installing a 4-ton unit. "Oh, my," she said. "How are you going to get something so big into my back yard?"
The confusion here is completely natural. HVAC and home energy pros find this story funny because when you say an air conditioner is 4 tons, we know we're not talking about the weight of the equipment. It's a number that tells how much heat the air conditioner can remove from the house in an hour. (Fro now, let's ignore the issues of nominal vs. actual capacity and AHRI derating.) A 4-ton air conditioner is one that can remove 48,000 BTUs of heat per hour from the house. (A BTU is a British Thermal Unit, approximately the amount of heat you get from burning one kitchen match all the way down.) For most people, though, 4 tons means 8,000 pounds.
It's cold enough to start harvesting, so get out your ice saw
Most pros also know how such a common term as “ton” has turned into a bit of HVAC jargon. Before Willis Carrier invented the modern air conditioner, people used to cool buildings in the summertime with ice harvested from rivers and lakes in the wintertime. A Green Homes America article quotes ice production figures from a 19th-century journal, Ice and Refrigeration, indicating that the 1890 crop from the Hudson River was about 4 million tons.
OK, so people used to cool and refrigerate with ice. How does that equate to air conditioning capacity in BTUs per hour, you ask? Well, let's get quantitative and find out.
The latent heat of fusion
When ice is below freezing and it absorbs heat, its temperature increases. When ice is at its melting point, 32°F, and it absorbs heat, its temperature doesn't change. Instead, it melts. If you've had a physics or chemistry class, you may recall that the amount of heat needed to melt ice is called the latent heat of fusion. In Imperial units, that number is 143 BTUs per pound.
That's actually a lot of heat to pump into a pound frozen water. Once the ice is melted into liquid water, it takes only 1 BTU per pound to raise the temperature 1 degree. So if you've got a pound of ice at 32°F, you put 143 BTUs into it to melt it completely. Then it takes only 180 more BTUs to raise the temperature of that pound of water from 32°F to 212°F, the boiling point.
Anyway, getting back to our main discussion: if you have a ton of ice, it takes (143 BTU/lb) x (2000 lbs) = 286,000 BTUs to melt it completely. You could do that in one hour or 10 hours or a year, depending on how quickly you pump heat into it. Somewhere along the line, though, someone decided to use 1 day — 24 hours — as the standard time reference here. If the ice melts uniformly over the 24 hours, it absorbs heat at the rate of 286,000 / 24 hrs = 11,917 BTU/hr.
Rounding that number up makes it a nice, round 12,000 BTU/hr. In air conditioning jargon, then, a ton of AC capacity is equal to 12,000 BTU/hr. There it is.
We've been talking about “tons of cooling” for a century
If you're wondering how this term got institutionalized, it was probably the usual way. People in the industry start using it, and then the professional organizations make it official.
An architecture website has a quote from 1912 that claims the American Society of Mechanical Engineers standardized it. It sounds likely, but their numbers don't work out, so I'm gonna go with Honest Abe (see image below) on this one and remain skeptical (until someone in the comments shows me what's wrong with my thinking anyway).
For the fearless: If you want to read some funny HVAC banter on this topic, check out this thread in the HVAC-Talk forum. And if you figure out what “heat of zaporization” is, let me know!
Thinking about making a change to your building's HVAC system? For more than 25 years, APPRO Development has been working as a general contractor with building owners in Minnesota, Wisconsin and North Dakota. Let us know how we can help you with your current building needs by contacting us here.
Our weekend started with a pleasant, almost fall-like, drive from Saint Paul to Two Rivers, Wisconsin. We had a wedding to attend in this quaint town. The drive took about five hours and was smooth sailing with little road construction (at this time). The trees had started turning and there was an abundance of nice Wisconsin farms alongside the road. We arrived in Two Rivers and checked into our hotel on the Lake Michigan waterfront. The hotel wasn’t great, but the location was. We were within walking distance of the historic downtown and only about 5 minutes from the wedding location.
Last night, I was watching an interesting program on Minnesota Public Television (TPT) called “Shaping the Urban Environment.” During the show they talked about the challenges and decisions communities are faced with when developing land in an area that has scarce and delicate natural resources. They began by explaining how commercial construction and even residential development of the past generations did not focus on their impact on the local environment, particularly. This piece just reinforced how important it is for development companies to make sure they are integrating green construction options for a sustainable future. This the best way for the commercial construction industry to make sure they are a focus on environmental sustainability. APPRO Development is committed to sustainable construction services and has been for 25 years.
Below is the link if you want to watch the whole program:
I know we’re all somewhat de-sensitized to the words “environmentally friendly” and “go-green” as companies abuse the terms as marketing approaches, such as labeling something “low fat” when it’s so high in sugar the full fat version would probably be healthier! ANYHOW… We, at APPRO Development and CERRON Commercial Properties, feel that we live on a pretty cool planet and would like to do our part where we can to take care of our neighborhood. In doing so, we are also finding ways for us all to save a bit of “green”, dollars that is!
We’ve made the switch over the past few months to create our subcontract agreements, change and purchase orders, and other documents using Adobe software so that we are able to send them via e-mail. The benefits in doing so are:
On December 17, 2010, President Obama signed the Tax Relief, Unemployment Insurance Reauthorization, and Job Creation Act of 2010. This law extends the tax credits for energy efficiency into 2011, BUT at lower levels. The levels revert back to those in effect in 2006 and 2007, which were 10% of the cost of the improvement, up to $500, with a $200 max for windows, and several other set maximums. Info per the EPA.