Calculating R-Values

R-value is a measure of thermal insulation in a house.  Each of your walls, ceilings, and floors has a certain amount of insulation and a corresponding R-value. The higher the R-value, the better the insulation, and the less heat is lost through that surface.  In this post, I will explain 2 ways to calculate R-value for a given surface.

Calculate theoretical R-value from wall structure

If you know how the wall or ceiling is constructed, you can calculate its R-value from its component material R-values. You can look up the R-values of common building materials on the Internet, and the R-values add when they are layered in the direction of heat flow. For example, rigid foam insulation is R-10, and fiberglass batt is R-13. Putting the foam and then fiberglass gives a total of R-23. Keep in mind that wall studs have lower R value than fiberglass batt, so those areas have a lower R-value. You can get an average R-value of a mixed surface by multiplying their respective U-value by the percentage of their area, then sum them. U-value is the inverse of R-value. A material with R-value of 10 has a U-value of 1/10 = 0.1. For example, a 2x4 studs area has R-7, and occupies 10% of the area; the fiberglass batt has R-14, and occupies 90% of the area. You can calculate the overall U-value as 10%*1/7+90%*1/14=0.0786. Convert back to R-value gives 1/0.0786=12.7. Note that the typical fiberglass batt filled walls don’t achieve the R value rated on the fiberglass batt because of the higher thermal conductivity of wood studs; this is also referred to as thermal bridging.

Calculate R-value from temperature measurement 

Instead of calculating the theoretical, optimal R-value of a given wall, you can calculate the actual, empirical R-value by measuring some temperatures. This can be done with a hand-held infrared thermometer. The best way to use an infrared thermometer is to hold it as close to the surface as possible, and avoid shiny surfaces.

Here's a table that will give you an estimate of wall R-values based on outside temperature and the temperature of inside surface of an exterior wall:

		Estimated R-Value
		1	2	5	10	15	20	25	30	35	40
Outside Temp (F)	40	20.4	10.2	4.1	2.0	1.4	1.0	0.8	0.7	0.6	0.5
	30	27.2	13.6	5.4	2.7	1.8	1.4	1.1	0.9	0.8	0.7
	20	34.0	17.0	6.8	3.4	2.3	1.7	1.4	1.1	1.0	0.9
	10	40.8	20.4	8.2	4.1	2.7	2.0	1.6	1.4	1.2	1.0
	0	47.6	23.8	9.5	4.8	3.2	2.4	1.9	1.6	1.4	1.2
	-10	54.4	27.2	10.9	5.4	3.6	2.7	2.2	1.8	1.6	1.4
	-20	61.2	30.6	12.2	6.1	4.1	3.1	2.4	2.0	1.7	1.5
	-30	68.0	34.0	13.6	6.8	4.5	3.4	2.7	2.3	1.9	1.7
	-40	74.8	37.4	15.0	7.5	5.0	3.7	3.0	2.5	2.1	1.9
		Interior wall T - exterior wall T

This table assumes your interior wall temperature is 70°F, but you can still use it even if your indoor temperature is a little different; the R-value will be less accurate if indoor temperature deviates from 70°F. To use the table, calculate the temperature difference between interior wall temperature and the inside temperature of the exterior wall that you want to know the R-value of. Look at the first column and choose the row that corresponds to the outside air temperature, look for the temperature difference closest to your measurement, then look up on top row for the estimated wall R-value.

Now, if you want to be more precise, calculate the R-value directly with the formula R=(T_h-T_c)/(T_a-T_h)*0.68+0.68, where T_h is the interior temperature of an exterior wall, T_c is the outside air temperature, and T_a is the indoor temperature. The indoor temperature can be measured on an interior wall or door or an object that should be in thermal equilibrium with indoor air. Outside air temperature can be measured on an outside object that’s in thermal equilibrium with outside air, such as a trash can or a deck. When using an infrared thermometer, avoid using it in daylight or measuring shiny objects. Also avoid measuring objects on or near the ground because the ground is often at a different temperature than air.

Note that all this discussion assumes no air leakage, no convection, no radiation, and no condensation. Only thermal conduction is considered here. Typically, air leakage or significant air movement would dominate heat loss so much that conduction becomes meaningless and usually the best thing to do is to eliminate air movement first.

Appendix

I will try to explain how the R-value formula is derived. First you need to understand the definitions of R-value and U-value. R-value is the thermal resistance of a material. U-value is the thermal conductivity, which is the inverse of R-value. 1/R-value = U-value. For example, an R-5 wall has a U-value of 1/5=0.2. U-value has the unit of BTU per hour per degree F per square foot (BTU/hr/F/sq. ft.). To calculate heat transfer through an R-5 wall with 70°F on one side and 60°F on the other side, just multiply its U-value by the temperature difference: 0.2*10 = 2 BTU/hr/sq.ft. To calculated the heat loss through a wall 8 feet high and 10 feet long, multiply by the area: 2*8*10 = 160 BTU/hr.

The model for calculating the R-value of a wall is that heat is moving from indoor (T_a) to inside surface of the exterior wall (T_h) through a layer of air film with R-value of 0.68, and the same amount of heat is moving from inside surface of exterior wall (T_h) to outside (T_c) through the wall with R-value of wall being the unknown variable. The equation is U_air*(T_a-T_h) = U_wall*(T_h-T_c). Solve for Rwall by rearranging the equation. In the above formula, you add another 0.68 at the end because the overall R-value of the wall includes an interior air film with R-value of 0.68. You can leave it out if you want just the R-value of the wall material itself.

Grass Update

My new strategy is to plant grass seeds every 2 weeks, keep the soil surface moist with sprinkler, and add fertilizer every 4 weeks.  I started in mid-July, and so far had seeded 3 times, fertilized twice.  The grass is growing deep green, but coverage is still not 100%.  Coverage increases after each planting, but it's not easy to get 100% coverage.  I spent effort pulling weeds out, especially the crab grass.  I also made a home-made rain gauge using a shallow bucket with inch markings to keep track of rain fall.  It is quite useful, because sometimes the rain would seem heavy, but accumulation is minimal, and sometimes it doesn't look wet, but had accumulated more than 1 inch.

repeated planting helps to increase coverage and keeping the ground surface moist improves the grass's survivability.  I think this strategy is working out better than previous strategy which is to plant a lot of seeds at once.

Dead Grass

I planted lawn grass last fall and this spring, and recently there was a 2 week period with unusually hot and dry weather, so about 40% of the last year's grass died, and about 90% of this spring's grass died.  I did a soil test yesterday, and found out that PH is around 7, which is good.  Nitrogen and Potassium are both very low, and Phosphorus is medium.  This tells me that the grass grows very slowly because there is not much nitrogen.  I suspect the grass died because it was not very mature, and the roots were not very deep yet, so it could not withstand the extended dry weather.  I went out and bought fertilizer and top soil.  The fertilizer is the local Country Estate brand by Hewitt's, and the one I am using is the winterizer product with 14-18-14 of NPK.  I first rake the ground to remove the dead grass, then put down 6 bags of top soil on this roughly 100 sq. ft. area, rake it even, apply the fertilizer, apply the grass seeds, rake and mix the soil and seeds, then water until it is very wet.

The recommendation I found online is to make sure the grass get 1 inch of water a week.  Putting down straw will help, but I didn't buy any this time.  The seeding instruction from Hewitt's recommends fertilize the new grass with the high phosphorus fertilizer after 1 month and after 2 months, until the grass is mature and strong.  I am looking forward to seeing the effect of the fertilizer, because this is the first time I am using fertilizer on lawn grass, so I should be able to observe the difference between this planting and last few times which was without fertilizer but with compost.

Road Runner Speed Test

Recently we switched from Road Runner Standard to Lite to save money. I just ran Internet speed test from speedtest.net. The results was 0.56 Mbps download and 0.12 Mbps upload. It is mostly inline with the advertised 768 kbps download and 128 kbps upload. Although this is much slower than Standard which is 10 Mbps/1 Mbps, we can save $300 a year if we can live with the slower speed.

Midterm Election

Election is coming up and I am curious about who is running and what are the issues they care about. First I will look up my polling place, which is the Niskayuna Town Hall, and they are open from 6AM to 9PM on Tuesday, November 2. I am in county district 3, assembly district 110, election district 17, senate district 44, and congressional district 21. So many district numbers. What do they mean? I go to http://nymap.elections.state.ny.us/nysboe/ and look up current government officials that represent me:

Governer: David Paterson

Lt. Governer: Richard Ravitch

US Senators: Kirsten Gillibrand & Charles Schumer

US Congressional District 21 representative: Paul Tonko

Population: 654,361

NYS Senate District 44 Senator: Hugh T. Farley

Population: 302,248

NYS Assembly District 110 Assemblymember: James Tedisco

Population: 131,594

And I go to the county web page to look up the current elected officials. In county district 3, we have:

James Buhrmaster, Martin Finn, Robert Farley, Brian Gordon, Susan Savage.

Two of these seats are up for election.

In our town I believe the Town Supervisor and one of the two Town Justice is up for election.

Candidates for NYS governor:

Andrew Cuomo (D/IP) & Bob Duffy

Carl Paladino (R/C/Taxpayers) & Greg Edwards & Tom Ognibene

Kristin Davis (Anti-Prohibition) & Linda Espejo

Charles Barron (Freedom) & Eva Doyle

Howie Hawkins (Green) & Gloria Mattera

Warren Redlich (Libertarian) & Alden Link

Jimmy McMillan (Rent is Too Damn High)

Dan Fein (Socialist Workers)

Kenneth Schaeffer (WF) & Elon Harpaz

Among these candidates, 4 have at least one attorney, and the rest are mostly some kind of activist. The political spectrum is very colorful, with many different groups represented.

For State Comptroller, we currently have Tom DiNapoli (D), and the other candidates:

Harry Wilson (R) Hedge Fund Manager

Julia Willebrand (Green) Educator, Progressive Activist

John Gaetani (Libertarian) Accountant

Rus Thompson (Taxpayers) Tea Party Activist

For Attorney General:

Eric Schneiderman (D) State Sen., Attorney & Ex-Police Officer

Dan Donovan (R/C) Staten Island District Attorney

Ramon Jimenez (Freedom) Attorney

Stephen Lynch (IP)

Carl Person (Libertarian)

Amy Young (WF)

For US Senators, both seats are up for election:

Kirsten Gillibrand (D)

Joe DioGuardi (R/C)

Vivia Morgan (Anti-Prohibition)

Cecile Lawrence (Green)

John Clifton (Libertarian)

Joseph Huff (Rent Is Too Damn High)

Bruce Blakeman (Tax Revolt)

David Malpass (Taxpayers)

Chuck Schumer (D)

Jay Townsend (R/C)

Randy Credico (Anti-Prohibition/Libertarian)

James Germalic (Black/White)

Colia Clark (Green)

Gary Berntsen (Taxpayers)

And for House of Representatives district 21, it's:

Paul Tonko (D)

Ted Danz (R/C)

The list of candidates was found on www.uselections.com

There is also this website called Project Vote Smart: www.votesmart.org that helps you see which candidate agrees with you most on major issues. They have the candidates for the federal government but not the state government.

For local state election, there's

BK Karamati or Jim Tedisco for Assembly

Susan Savage or Hugh Farley for State Senate

I am ready to vote on Nov. 2

Furnace

Recently I went through the process of shopping for a new furnace and A/C because the existing one was more than 35 years old. The old one still works, but the service technician said the heat exchanger is showing signs of cracking and there is danger of the exhaust gas mixing with indoor air. The old furnace is rated to output 100k BTU while using 125k BTU, which gives it a 80% efficiency. Given its age, the efficiency is probably lower than that. The chimney pipe gets very hot when it is running, indicating a lot of heat is wasted through the exhaust. It is loud when it is running the blower fan, which is a belt driven fan. The old electronic air cleaner creates zapping sounds when the air is flowing.

I got estimates from 8 different installers. Each one presents to me a proposal for a particular brand and model of furnace. Some sell Lennox, some sell Carrier, some sell Trane, some sell Rheem, and some sell Bryant. I quickly found out that Carrier and Bryant means the same equipment just with different labels. Trane is the same as American Standard, and Lennox owns Service Experts, which has 2 branches in my area. Interestingly, the 2 companies under Service Experts seem to be competitors of each other and they don't use the same system. Rheem has good reputation and it is physically shorter than other brands.

From reading online, I got the idea that good furnace installers do Manual J load calculations to know the house's heat gain and heat loss for sizing the system's heating and cooling capacities. Of the companies I called, only 3 would do it. Some installers just look at the existing furnace and see what capacity it is rated and go by that. Most of them just decide the furnace size by experience or by square footage.

After I got some initial choices of equipment, I started reading more about them and came to understand that Lennox furnace can modulate its heating output from 60% to 100%, but it does not use a communicating thermostat and so it does not know how far it is from the set point temperature. It decides its heating output based on history data and tries to guess what the appropriate heating output should be. Rheem makes a modulating furnace that uses a communicating thermostat, but the efficiency is 92%, which does not qualify for the federal tax credit. Rheem has 95% efficient models but they are not modulating. Bryant/Carrier has a 3 stage furnace that uses communicating thermostat, which is what I eventually installed. The communicating thermostat talks to the furnace and other connected equipment using a series bus, so it only requires 4 wires: 24V supply, ground, data A and data B. I am not familiar with what data A and data B are, but my guess is that one of them is a clock signal and the other is the actual data line. The thermostat talks to the furnace and automatically discovers what equipment it is connected to and automatically adjust its settings to fit the house. For example, it tests the static pressure of the duct system and finds the appropriate motor RPM to create the appropriate CFM of air flow. The thermostat knows how far the room temperature is from the set point and see if it is moving towards or away from the set point. The furnace would change its heating output accordingly to drive the room temperature towards the set point.

Another thing I liked about Bryant is that their technical literature such as install manual and product information is online and not too difficult to find, whereas the Lennox documents were almost impossible to find.

I also looked into options for filtering. There are media filters, electronic air cleaners, and HEPA systems. The media filters come in different sizes, but the one I am looking for is the 4 7/8" thick kind that comes with MERV rating between 8 and 16. The issue with electronic air cleaners is that they require electricity, create ozone, and need expensive replacement UV light bulbs every year. The HEPA filters are typically by-pass type filters that cleans a portion of the air going through the furnace, and the install cost is high. I think the media filter with a high MERV rating will be sufficient for me.

For humidifier, I gathered that there are 3 types: by-pass, fan powered, and steam. The by-pass one takes air from the return duct, passes through the humidifier, and goes into the supply duct. The fan powered models mount on the supply duct and blows air over the water in the humidifier and into the duct. The steam ones also just mount on the supply duct and it makes steam which goes into the supply duct. I didn't get a humidifier, but I think I will get the steam type if I decide that I need a humidifier.

Computer Games

Recently I bought a new real time strategy game for my computer. It is called the Sins of a Solar Empire. They call this game RT4X, for real time exploration, expansion, exploitation, and extermination. From the name, you can guess that it has to do with spaceships and planets, and that's correct. This is like other real time strategy games like Starcraft that you have to gather resources to build up a fleet of war-fighting machines, and destroy the opposing forces. Unlike Homeworld, this game doesn't have much of a story. It doesn't have a single player campaign, and it doesn't let you control the ships in its z-direction. Everything is still controlled in a plane. I think that's the right thing to do, because it's a game, and being able to go up or down in the space doesn't add too much strategy but complicates controls a lot. In a way the game is less realistic because your planet defense is laid out in a circle rather than a sphere, which should be the case in real life. In terms of artistic values, Homeworld did a better job. The Sins is a true strategy game. It is almost like chess with a spaceship overlay. After playing a few games, I am getting the hang of it, but I also feel it can get boring quickly. I probably won't be able to win against many computer players, but it probably will get boring at some point. I am not sure if I want to go online playing because it will probably take too much time and there's no way to pause.

Upcoming games that I am looking forward to are: Star Wars the Old Republic, Call of Duty 7, and Diablo 3. These 3 games will be out 2010 or later, but they look like they will have high entertainment values. The Old Republic is an online mass multiplayer game similar to World of Warcraft. Personally I like the Sci-Fi genre a bit more than swords and magic. There was a Star Wars MMOG before and I have watched a friend play, and I thought it was not too sucessful. Hopefully this time they will make a great game out of it. Call of Duty 7 is a sequel to Call of Duty 4 Modern Warfare, which I played and enjoyed immensely. The Call of Duty series is a first person shooter that is made like a movie, and that's the main reason I like it so much. It really makes you feel involved and actually fighting on the battle field. I played Diablo 2 when I was in high school, and it was a fun game. It is like an RPG with a lot of action, and it also has a very involved story line. The new game looks like it will be as much if not more fun. It look as grotesque as ever though, so it is definitely inappropriate for children to be close by.