SPLIT SYSTEM OR ROOFTOP?

HybridHeat Split systems instead of a "Rooftop" unit

Which costs more?


$10,000 HVAC Packaged Rooftop Unit.

– OR –

$20,000 Hybrid Heat “Split System.”


Do you know the answer?


Actually, it’s a trick question

 

 

The short answer is; “I don’t have enough information.”


The additional information necessary to determine which costs more should include average life expectancy, maintenance expense, and annual energy use.


Here is a sample analysis comparing a common rooftop to a Hybrid Heat split system (calculated by Carrier “OpCost” which utilizes a “Wrightsoft” heat load calculator backbone):


  • 120,000 BTU heating load, 5 ton cooling.
  • 14610 area code, $1.35 Therm gas cost, $.10 KWH electric cost.
  • Annual energy cost $3674/$5013.

The average split system lasts 15-25 years.  For this exercise I’ve assumed 17.  The average rooftop lasts 10-15 years.  For this exercise I’ve assumed 12. Also, I put the install cost of the split system high.   I find it’s better to under promise and over deliver, so these assumptions are skewed to the advantage of the rooftop.


Maintenance and repairs on rooftops is somewhat higher, but I have not factored that into my calculations. No assumption for increase in energy cost is factored in either.  Also not calculated, but assumed in the package costs is an energy recovery ventilation system on the Hybrid v/s fixed intake makeup air for the rooftop.  Makeup requirements could increase the disparity in energy use significantly depending on occupancy assumptions.


So, what is the “TOTAL ANNUAL COST” for both packages?  Depreciation of the Hybrid system (true annual purchase cost) is $1176 per year.  The rooftop is $833.  On its face the rooftop still looks cheaper, right? But when you add in energy cost, here is the annual result:


$4850 for the Hybrid split system, and $5846 for the rooftop.  The split saves $1000 per year! Put another way, total cost of the split including energy use is less then just the energy bill of the rooftop.


So why are rooftops the common “go to” answer? For a couple reasons:


First, in a large majority of cases there is a disconnect between initial cost and lifetime cost. Often the building owner and equipment decision maker is only exposed to initial cost, so incentive to reduce energy cost is not part of his equation. If the owner IS the tenant, they don’t associate higher equipment cost with lower energy cost (or vice versa).HybridHeat Split system instead of a "Rooftop"


The second disconnect is knowledge. How many HVAC Salespeople understand this opportunity, or want to risk bringing it up?


The third disconnect is time. For the HVAC Salesperson that does understand, the additional difficulty and time, not to mention reduced likelihood of making the sale, cause this approach to be a huge net looser.


Forth, and most important, is the consumer. If the consumer doesn’t start from a place of total cost they are unlikely to get this type of recommendation.


Better equipment costs more up front. This approach is not going to look advantageous if they are using an initial cost or “low bid” replacement strategy.

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Understanding Humidity – incredibly important

Until recently I had no clue about how moisture vapor worked.  The more I understand about Humidity, the more it blows my mind how incredibly important managing humidity is to energy, comfort, health, and durability.   Recently I ran across a few articles in USA Today that do a nice job of laying the groundwork for understanding humidity:


Understanding Humidity – lays the groundwork for why understanding humidity is important.

Wrong Humidity turns your house into a HASSLE – discusses problems from static and dust to mold, and how through simple moisture management these comfort and durability problems can be avoided.

How low humidity dries out your house – this short article does a nice job explaining why indoor air dries out in the winter.

Getting a Handle on Humidity – explains RELATIVE humidity, DEW POINT, and what happens to humidity as temperature changes.

Just as Heat goes to Cold, Moisture goes to Dry.  The velocity of this movement for both heat and moisture is a function of DELTA, or size of the difference.


Please feel free to post questions or comments about your situation “relative” to humidity.



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QUESTION AND ANSWER SECTION – Where your good questions benefit everyone.

I will post interesting questions and my answers here for now.   Please keep the questions coming!

Comments (9)

ANNE PETERSON!!

WOW, guess I shouldn’t sleep in on Saturdays!  First let me say it is really flattering to be referred to as an Energy Guru by Anne Peterson. Thank you for the complement!

NYSERDA has so many different energy programs, commercial, municipal, not for profit, that finding information about residential can be daunting.  This web-site will continue to evolve, it is in it’s infancy and suggestions are welcomed and encouraged.

If anyone feels this site is to cumbersome for them to find the answers they are looking for please drop me an e-mail or call 4664-nrg, that’s 466-4674.  Here’s an excerpt from my “Landlord” page:

There are great programs available to help landlords take a comprehensive look at energy savings opportunities.  Cutting energy costs by 70% is not unheard of. Energy modeling allows quantification and prioritization of improvements BEFORE the work is done, removing guesswork.

FREE IMPROVEMENTS – EMPOWER

EMPOWER is a weatherization program for NY residents whose household income is below 60% of median family income.  Most of the work done through EMPOWER  is FREE.

I utilized EMPOWER for one of my rental properties and the tenants received an energy star refrigerator, all the doors had weatherstripping replaced, penetrations and rim joist in the basement were spray foamed, duct work was sealed, and insulation was added to the attic.

(Click here for 80% Assisted Income Guidelines and multiply by .75 to arrive at 60% median income cut off.)

MORE EMPOWER INFO HERE

$5,000 Grants – Home Performance with Energy Star

At 80% of the median family income (Assisted Income Guidelines) the incentive is $5,000 on a $10,000 worth of improvements for one unit.  If credit worthy the remaining $5,000 can be financed over 10 years for $55.50 per month (5.99%).

If you qualify for the grant program and the loan program, usually your energy bill goes down by more than your loan payment.  This means money you were sending to the utility company is paying for substantial improvements to your home.

You are spending the money anyway, why not have it go to improving the comfort, value, and efficiency of your home?

MORE HPwES 50/50 INFO HERE

$10,000 GRANTS – Home Performance with Energy Star

A maximum subsidy of $10,000 on $20,000 of improvements for 2-4 family houses!


Ted – 11am


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BEWARE of “Common Knowledge” and “Conventional Wisdom”

Blood letting was once thought to cure all sickness.

People tend to like easy answers.  This creates problems, particularly when the questions are complex.  Often conventional wisdom ends up being a one size fits all answer that is the right answer 20% of the time, and ends up creating headaches for 80% because it is the wrong answer for them.  House as a system building science takes a “big picture” look at how various components interact and considers how changes to one component may have unintended consequesces some place else.   More later…

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SPRAY FOAM ALBUM

For those interested is pictures of spray foam jobs, click HERE


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Hybrid or DUAL FUEL Heat – air source heat pump and natural gas

OOPS, didn’t set heat pump to lock out at 40 degrees.  10 degrees outside and turns out the heat pump is still heating the house – to 70!  So, house that used to have an 80,000 BTU furnace can easily be heated with roughly 32,000 btu at 10 degrees.  Guess that goes to show how much fluff heat loss calc’s have in them!

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SMALLER is better (I know – counter intuitive), for a lot of reasons:

I find a lot of people are unhappy with recently replaced equipment.  Usually this is because they made the mistake of “going one size up” or worse, didn’t have the equipment sized at all.   HVAC equipment is like running shoes, the better the fit the more comfortable and efficient it is to run.


There is a lot of “fudge” factor in heat loss  calculations.  For greatest efficiency and comfort they should have gone one size DOWN.  Over sized equipment means challenges to balance, control, efficiency, humidification, and dehumidification.

MORE SOON – if you have questions about this or any post please call me.

Comments (1)

28 Degrees and furnace only runs for one 15 minute period every 2 hours!

Was at my Mother’s house last Wednesday evening for about 2 hours.  It was about 28 degrees outside and for the first hour and 45 minutes the furnace didn’t run! I could only tell it came on because from my seat I was watching the Infinity Thermostat.

They’d been mentioning how the house temperatures seemed not to fluctuate, I thought it was because the furnace was so quiet and provided such gentle heat – turns out it’s because the house loses heat so slowly!

We did a lot of air sealing as well as installing a complete Carrier Infinity Hybrid Heat system with 5 stages of heat and 2 of cooling.  It seems more about the weatherization then the furnace…  Click here to look at the pictures


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Power of Condensation

The power of condensation – condensation and evaporation are what allows refrigeration to occur.  Condensing combustion appliances gain significant advantage via this mechanism as significant heat energy is transferred when water vapor (a byproduct of combustion) condenses on the secondary or condensing heat exchanger.


Latent Heat of Vaporization of Water:  It takes 1 BTU to increase 1 pound of water’s temperature by 1 degree.  So to increase the temperature of a pound of water from 211 degrees to 212 takes 1 BTU of heat energy.  To take that same pound of water at 212 and convert it to steam at 212 takes nearly 1000 BTU’s.


When the process is reversed and gas changes back to a liquid (condensation), that energy it took to convert to steam is released.


One of the primary byproducts of natural gas combustion is steam.  By designing a device to harness the energy of this steam through condensation a tremendous amount of previously wasted energy can be captured and used to heat our homes.


So, a lot of energy is absorbed through evaporation and released through condensation (principles used for cooling).  Having that condensation occur within a combustion heating device and capturing that heat rather than simply pumping it outdoors makes a LOT of sense.



For more – Read Principals of home inspection, introduction to heating.

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