Is Pipe Insulation Effective?

It’s that time of the year, when the weather turns cold and people start to think about winterizing their home to reduce heating costs.  Usually it takes the first winter heating bill to provide the motivation to undertake this task.  With this in mind, I would like to talk about pipe insulation.  Specifically, the foam wrap insulation you can find at any hardware store (http://www.homedepot.com/h_d1/N-5yc1v/R-202318552/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053)

In my case, I started to look into pipe insulation for an entirely different reason.  During our home inspection, we were told that much of our copper pipe was run alongside the HVAC ductwork.  In some spots, the metal strapping for the duct was touching the copper, which would cause some galvanic corrosion.  The simple fix would be to wrap the pipe with something to prevent this contact.  When I stumbled across this foam pipe insulation for about a buck for 6 feet, I was sure I had found my answer. 

Since I was going to the trouble of going into the crawlspace, I figured I should buy a bunch of these and wrap as much copper pipe as possible, because my pipe is exposed to the cold outside air in the crawlspace, so I thought there could be quite a bit of energy efficiency gained.  Plus, as the master bathroom is at the opposite end of the house, I had noticed it takes a minute or two in the morning to get hot water.  My new hope was to be able to shower or wash my hands in the morning without having to waste water and time waiting for it to get hot.

During the installation of these foam pipe covers, I found it difficult to get the foam insulation in different areas, whether because of T-joints, strapping or bends.  I also didn’t buy enough foam, so there was still some exposed copper.  This is when I started to think about running a CFD analysis on this problem.  If there is some exposed copper, because of its excellent conductivity, will the heat just move to this opening, rendering all my insulation efforts moot?  Did I need to make the long crawl through my crawlspace to put more pipe wrap on, or were these little portions of exposed pipe inconsequential compared to the many feet of newly insulated pipe. 

For this analysis, I used our general purpose CFD tool, FloEFD.  I needed some baseline numbers, so I modeled a 1 meter length of copper pipe, then I would analyze that copper pipe completely covered with the insulation (best case), then introduce a representative “gap” in that insulation for my current setup.  From some research I found that hot water comes from the tank at about 50 degC, and a shower can draw about 2.5 gal/min.  For the air, I wanted to simulate the worst case air temperature, which I think in the winter in my crawl space would likely be about 5 degC (above freezing for sure, though preventing pipe freezing is an added benefit of these pipe insulations). 

Now we all know convection heat transfer improves with air velocity, so I wasn’t sure where to go here.  From my previous crawlspace blog, where I looked at my soil water issue, I found the air speed down there was sluggish to say the least.  Yet, the copper pipes running to my shower run within 1 ft of the crawl space vents, and I could feel a breeze at that location.  So I decided I would need to run a no wind and a 1 m/s wind case.  Below are my results. 

 
Now, if you are a person that just spent $20-$30 bucks and half a morning in a dirty, cobweb filled crawlspace, you will instantly get the main gist of these results.  First, the water temperature is the same at the end of the pipe for all 3 cases.  Maybe 1 meter of pipe length is too short to represent the 60 ft of pipe leading to our bathroom?  I would argue that if they are the same to 1-2 decimal places, then there isn’t going to be a very perceptible difference even for 20 times longer pipe. 

The other main result was that the heat transfer rate was basically the same.  In fact it’s slightly worse with insulation compared to without, due to the insulation having a larger surface area.

Copper Pipe, No Wind

Partial Foam Insulated Pipe, No Wind

 

                                  

Fully Foam Insulated Pipe, No Wind

 

Now, looking at the results for the with wind case, where we see a bit of a reversal on the heat loss trend.  Now that forced convection is dominant, the increase in surface area for the insulated pipe doesn’t seem to be a factor.  At the end of the day though, the water temperature is still pretty much the same value.

 

Full Foam Insulated Pipe with 1 m/s wind

 
 
It’s at this point when I started to look at this problem in a different light, as I didn’t want to have wasted money putting on insulation that isn’t effective.  My new thinking is that a steady state analysis of this problem is not ideal.  We will never be running the water for hours on end.  My goal is to have the hot water that is in the pipe to stay hot for as long as possible so that it doesn’t take 5 minutes of running the tap to get hot water at the sink/shower.  This wastes water and energy and my money, and that’s what I’m hoping gives me my ROI for my foam insulation investment.

With that, I decided I needed to simulate this as a transient analysis, starting from when the water has stopped running and timing how long it takes for the water to sufficiently cool.  I figure that would be somewhere around room temperature when you would think the water isn’t “hot”. 

At this point I only simulated the wind case and full/no foam, as I’m more interested in the worst case scenario (and justifying my insulation purchase).

 

Now this is what I’m talking about.  Without insulation, the water in that pipe gets to a chilly 10 degC in about 11-12 minutes, whereas with insulation, the water doesn’t get that cold till 100 minutes.  That’s a 9 times improvement for $1 per 6 feet of pipe.  It’s hard to argue with that return on investment.  Now, I usually shower first thing in the morning, so the water won’t stay hot throughout the night, so I’m out of luck there.  For everyday washing of hands and kitchen stuff, we will definitely be wasting less water because of these pipe wraps, and that’s what matters.

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Posted January 17th, 2012, by

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About Travis Mikjaniec's Blog

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12 comments on this post | ↓ Add Your Own

Commented on January 18, 2012 at 2:33 pm
By Robin Bornoff

Travis, excellent application. I wonder how Flowmaster would address this problem?

Robin.

Commented on January 19, 2012 at 9:38 am
By scott ferreri

Nice work. Very practicle example that I have also wondered about myself in using these pipe wraps.

Commented on January 24, 2012 at 11:25 am
By Roger Anthony

This is fascinating stuff!
Please advise what type of pipe wrap and its thickness.
I have spent ages insulating my pipes and have been really disappointed with the heat loss after the insulation was applied.
It seems to me that all the insulation on sales is pathetic.

Commented on January 24, 2012 at 11:44 am
By Travis Mikjaniec

The insulation I used was similar to the link provided to Home Depot. It’s a foam tube with a slit down one side. Some have a adhesive strip in the slit so it seals tight once it’s been installed, but I just used the cheaper ones and taped it shut.

The reason most pipe insulation leaves a lot to be desired is due to the fact that unlike attic or wall insulation, when you apply insulation to a pipe, you increase the surface area for heat transfer. For a attic or a wall, it’s a flat surface so the surface area stays the same when insulation is put on top. Wikipedia has a good paragraph on this on their heat transfer page http://en.wikipedia.org/wiki/Heat_transfer . At some point there is a critical radius where as the radius of your pipe + insulation increases you get to a critical radius where your pipe would be losing the maximum amount of heat.

As my results showed, the insulation I added is in that zone where the increase of surface area actually meant my pipes were losing slightly more heat in the steady state and natural convection situation. So if you run hot water a lot, like in a business or in a house with people using hot water a lot throughout the day, adding pipe insulation may not help (or you need to make sure you get the biggest thickest one possible to stay out of that critical radius zone). For a small family home where the hot water sits in the pipes for an extended period of time, then the insulation made a huge improvement.

Commented on February 28, 2012 at 12:55 pm
By Al

How wold this insulation type be different from one made with fail (http://www.pexuniverse.com/radiant-heat-insulation)

Commented on February 29, 2012 at 5:41 am
By Jean

Hi there,

What’s up, just wanted to tell you, I loved this post? It just so very helpful. Keep on posting! http://www.homebuildersaustralia.com.au/melbourne-builders.html

Commented on July 11, 2012 at 6:04 am
By Lee Price

Very informative post there. Insulation of all types can help when it comes to energy efficiency and saving heat. My company, http://www.dgi.org.uk , deals mostly in wall and loft insulation and we are constantly looking to highlight the importance of such technologies.

Commented on July 24, 2012 at 12:24 am
By Antony

Thanks for writing this information to the web.
Here is my homepage – solar hot water system brisbane

Commented on February 12, 2013 at 1:50 am
By Insulation Adelaide

Pipe insulation is beneficial to those who may live in an environment that tends to have extreme temperature changes, especially places where the temperature can drop drastically. Pipe insulation will prevent frozen water pipes. Thanks for the post…. Willing to see more from you..

Commented on February 18, 2013 at 4:19 am
By Insulation Adelaide

Using insulation while renovating your old home is a smart way of renovation. Now a days most of designers advice you to go with insulation while renovation. Insulation keeps your home long lasting avoiding damp on walls. If you are thinking about a good insulation then pipe insulation is must suitable for your house it avoids water damping due to leakage.

Commented on March 12, 2013 at 2:29 pm
By Bah, humbug

Interesting. However, just having done the calculation to see how much water and energy savings I’d get, I’m not convinced it’s worth the effort. For a 35 foot run of pipe (25 feet of 3/4in pipe and 10 feet of 1/2in pipe) it takes 0.675 gallons of water run down the drain to get hot water to the faucet. That costs $0.00135 where i Live. The energy to heat that 0.675 gallons of water would cost me $0.00838. I save a total of not quite one cent each time I run that faucet until it gets hot. Not seeing the ROI. Now, if your goal is not wasting the water, good for you. Just know you’ll never make the money you spend back.

Commented on July 14, 2013 at 5:48 pm
By Travis

great analysis.

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