Insulation beyond ROI

Brad White_9

Some more information might round out a better answer.

1) Is there a timer and aquastat and how is it programmed? (Time of day, definite off periods and no gravity/ghost flow for one.)

2) Where is the aquastat located? If on the return line back at the tank you are keeping the return line hot whereas if near the furthest fixture you are doing your best effort.

3) What temperature is the setpoint? Occassional bursts may pay dividends even if not instantaneous at the fixture.

4) What is the actual temperature in the subject return line (assuming setpoint is upstairs near the fixture)? Tepid, ambient or hot hot hot..

Now for the odd part: You may want to figure your losses (there will be some of course) as a summer loss only. In winter it all goes to heating the space, eventually, assuming the pipe is well enough within the envelope.

OK, granted that is neither controllable for heating nor dependable, nor really worth considering as a heating source. But you just know it is heating your house at some point.

Summer? I would count it against AC loads to a similar degree. Even if no AC, the DHW temperature loss is not helping anyone in the summer.

So, to ROI:

Hours of Use?

Temperature setup?

At what ambient are the losses during which season?

AC or Not?

Cost of energy/generation


Here are some quick figures from Siggy's HDS pipe insulation module:

120F water, 1.0 GPM in 1/2" Type M copper, 25 feet of length all in a 75 degree ambient:

Bare Pipe: 309 BTUH

3/8" Armaflex: 153 BTUH (3/8"? Can you spell HD?)


1/2" Armaflex: 134 BTUH


3/4" Armaflex: 112 BTUH


1" Fiberglass: 88 BTUH

You can see how the diminishing returns occur with the little bit more. Still you also have to know your energy/generation costs of course.

Does this help get you started?

Dan_15

Insulation beyon ROI on recirc system

OK
So let's say we are doing a gravity driven recirc system in a multi storey house. How much is too much insulation on the lines.... :-)

Say we have 1" going up and 1/2inch on the return...would you do:
(1) Armaflex tubes..
(2) Armaflex tubes with an additional fiberglass tube 'overcoat'

It's tough to do heat loss calcs on these materials. How can the customer know when they have passed the ROI?

The 1" tubes are already insulated with armaflex and no longer accessible. This fit would only apply to the 1/2" tubes.

I know that ideally we would do both, but considering the 1/2" in isolation, how can we calculate the additional Return on Investment (ROI) of the extra insulation



come on....someone come up with some smart Math :-)

Mike T., Swampeast MO

Not knowing the material/installation costs involved, I can't calculate ROI, but since you do know, here's some data that should help.

While heat loss from bare copper (I'm assuming copper tube) is notoriously variable depending on the surface condition of the tube, about 0.27 btu/hr per lineal foot of ½" tube per degree of temperature difference.

½" Armaflex has a thermal conductivity of about 0.54 btu/hr per square foot per °F of temp difference, so...

½" copper tube is 0.625" diameter. 1' of such tube has 0.3068 square feet.

0.3068 * 0.54 = 0.1657 btu/hr per ° difference per lineal foot.

Let's assume 120°F tube, and 60°F ambient air for a difference of 60°F.

The bare tube will loose .27 * 60 = 16.29 btu/hr per lineal foot.

With ½" armaflex, 0.1657 * 60 = 9.94 btu/hr heat loss per lineal foot. That's about a 39% reduction in heat loss compared to bare tube.

For simplicity let's say there's 100' of ½ copper tube. In a year the bare tube would loose 100 * 16.29 * 24 * 365 = 14,270,040 btus or 142 therms. BUT, let's say that 3/8 of the time, that "lost" energy contributed to heat demand.

So, about 89 therms "wasted". At $1.50/therm that's a cost of $134 per year.

The ½" armaflex will reduce "wasted" heat to 89 * 0.61 = 54 therms for cost (at $1.50/therm) of $81 and a net savings of $53 per year.

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For adding another ½" of fiberglass on top of the armaflex:

AT BEST, and VERY nicely applied, ½" of fiberglass will further reduce heat loss by about 3.43 btu/hr per lineal foot @ the stated conditions (60°F temperature difference).

So, 100' * 3.43 * 24 * 365 = 3,004,680 btus. Again assuming that such energy is "wasted" 5/8 of the time, that's about 1,877,925 btus or 19 therms of additional savings. At $1.50/therm that's $29 bringing the total savings (compared to bare pipe) to $82 and reducing annual cost to $52.

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1" armaflex (definitely available but likely not "stock" in many places) would reduce loss by about 70% compared to bare tube.

Using the above numbers, that would reduce "wasted" therms to about 27 ($41 @ $1.50) therm for annual savings of 62 therms or $93. ($11 per year greater savings than the added ½" of fiberglass which will likely require significantly more labor to install nicely...)

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Please examine for stupid math errors or totally bogus assumptions!

steve b_18

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In my travels around the web I bumped into a free insulation thickness computer program at http://www.pipeinsulation.org/pages_v4/details.html that "calculates the economic thickness of insulations based on return on investment for chosen fuel cost, installed cost, tax rates, maintenance, etc".

I haven't tried this software yet, so I don't know how well it works, but it sounds like it might be a good tool for answering questions about the economics of pipe insulation.

Steamhead (in transit)

ROI will increase

with fuel costs. Insulate them to the max.

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Brad White_103

Their 3E program ROCKS!

And... it is free.

I recommend it. I find it invaluable for determining the optimimum thicknesses. You can use safety (surface temperature), energy savings and other bases of design across a wide range of materials.