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Thread: The cost of efficiency

  1. #1

    Default The cost of efficiency

    Some context...I buy and renovate houses in the urban northeast. While their condition at purchase ranges from okay to not so hot, they are usually structurally sound. That said, they almost never have adequate insulation...if they have any at all...and building envelops offer little in the way of a thermal barrier. Of considerable importance is the fact that apartments in these houses often rent to Section 8 tenants.

    As a landlord I can opt to pay utilities or have the tenant pay, the difference being the amount of rent money I receive from the local housing authority (more if I pay). In either case, the amount of money earmarked for utilities is not sufficient to cover today's wildly inflated gas and electric costs. Now, to the heart of the matter.

    I am in the midst of rehabbing a three family house in Newark, NJ. It needs a completely new heating system...actually three systems...and I have opted to go with direct vent, gas-fired boilers feeding hot water baseboard registers, one boiler for each floor. Hot water will be provided by three, 199k btu, tankless water heaters. My goal is to make this house as green and as energy efficient as possible, while being mindful of a tight budget, in order to reduce utility costs. The reason is that even though the rent might be paid by the housing authority, astronomical heating bills will make the house unaffordable for the tenant or a losing proposition for me, depending upon who is paying the utility costs. So, here is what I am wrestling with: given the fact that it is economically unfeasible to seal and insulate the entire building envelope is there a benefit to paying the premium for high efficiency boilers (90% or greater) or would I be better off with lower efficiency (low 80s) while investing the price difference in more insulation (but still not the whole building)?

    In advance, thank you for any guidance you can provide. The efficiency of heating systems in affordable housing is an issue that will take on increasingly more importance as time goes on.

    Brian McCabe

  2. #2
    DIY Member cattledog's Avatar
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    Brian--

    "The efficiency of heating systems in affordable housing is an issue that will take on increasingly more importance as time goes on."

    You are to be commended for trying to make this work out. The potential cost savings of energy efficiency are significant for Section 8 tenants.

    If you are going to use hot water base board heating, you should consider a 50/60 gallon indirect hot water heater coupled to the boiler. You then have the advantage of a high efficiency boiler providing the dhw instead of the tankless which have lower AFUE. My calculations indicate that the standby losses maybe less important than the efficency difference between the appliances. The tankless are best for "endless" hot water, but I'm not convinced of the actual energy savings.

    Your choice between insulation and boiler efficiency should be a straight forward analysis once you have the heat loss study for the building. One additional thing to consider is adding enough radiation so that you can heat the building with lower water temperatures. At lower water temperatures you can consider modulating and condensing gas boilers. Adding "outdoor reset" will adjust circulating water temperature down when its not too cold outside, and will provide additional efficiency and savings in the shoulder seasons.

    I don't know if you have a three story building, but it you do there will be significant heat loss differences for different floors. You may be able to leverage off that fact to make the building as a system work in your favor if you supply the heat.

  3. #3
    DIY Member cattledog's Avatar
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    Here's a link to a report from Brookhaven National Laboratory about condensing boilers used with hot water baseboards and indirect hot water heaters.

    http://forums.invision.net/Attachmen...hment_ID=34000

  4. #4
    Computer Programmer Bill Arden's Avatar
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    Heat loss in larger buildings is dominated by air leaks.

    Personally I would suggest spending the money fixing air leaks and insulation.

    The furnace or boiler can the be changed out latter to a much more efficient system like a ground source heat pump.

    I see oil and gas staying high, while electric leveling off in terms of price.

    Edit: It's also good to think in terms of "Cap in heat" and "tub the cold" in that you get a bigger return when you seal leaks at the top floor and the basement.

    You might also have to plan for some sort of fresh air.
    Last edited by Bill Arden; 07-04-2008 at 08:58 AM.
    Important note Ė I donít know man made laws, just laws of physics
    Disclaimer: I'm a big fan of Darwin awards.

  5. #5
    Engineer Furd's Avatar
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    I see oil and gas staying high, while electric leveling off in terms of price.
    That depends entirely on how the electricity is generated. If it is from oil or gas the price will have to mirror the cost of the fuel. Coal will follow general inflation for the most part and hydro will have the least increases due mostly to general inflation. Nuclear is anybody's guess.

  6. #6

    Default Energy Efficiency

    If you want to incerease efifciency with little cost then keep the condensor clean and free of corrosion. This may be a Catch 22 since common cleaners are not good for the environment. Go to www.adsil.com and then to the HVAC section. You can get corrosion protection without loosing heat transfer and you also can get a very hydrophobic surface that keeps clean without using harmful cleaners.

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