Oil Heating Airflow Test

    - with Darrell Udelhoven - HVAC RETIRED - udarrell
     

HVAC Efficiency Overview My Audio overview; listen while you do other things
My Scan of My Oil Furnace Blower Curve 

Air Conditioning Rip-Off Scams

Below is an example of this problem with a (Thermo Pride OL 11 oil furnace). OIL HEAT FUEL COST COMPARISONS New!
The low airflow probable cause is "an unbalanced airflow heatload through the evaporator coil, along with an airflow restriction due to the evaporator coil being too close to the large oil furnace heat exchanger. | Oil Furnace Airfow Problems HVAC-Talk FORUM @#10

A Major "Oil Furnace" Airflow Problem Fix
Regal & Hallmark & nearly all Oil Furnaces - Installation manuals
http://www.boyertownfurnace.com/ProductDocuments/index.aspx
Download the installation & service manuals
To find the information below; Use within the pdf search:  at least 6” above
Or use down arrow to P-8 & scroll down a-ways...

http://www.boyertownfurnace.com/ProductDocuments/HallmarkONLYManual042909.pdf

understanding airflow science - in respect to the evaporator coil being too close to the large Oil furnace Heat Exchanger.

If the oil furnace is used in connection with summer air conditioning the evaporator coil must be installed at least 6” above the oil furnace for proper airflow. Distances less than 6” will result in decreased airflow. Make sure outlet supply takeoffs are NOT blocked by the coil. In all cases, refer to the manufacturers’ data for static pressure losses to ensure the total system static pressure does not exceed 0.5” WC.

*Basics Featuring the Testo 556 - Video of a very thorough A/C Testing setup 2/26/11

MOLO Plumbing & Heating SW WI & Tri-state area (888) 795-9281 sets the A-Coil at least 6" above a Thermo Pride OL 11 Oil furnace. They know the importance of unrestricted airflow! http://www.molocompanies.com/plumbingandheating/index.html

When installing evaporator coils on an oil furnace, due to the extra-large heat exchanger that is near the top of the furnace, the coil should be set well above the heat exchanger using sheet metal to channel the air into the air intake of the evaporator coil. This will optimize the directional velocity which will increasing the flow and throw through the supply diffusers.

When the evaporator is set directly on top of the furnace it results in a restriction of airflow along with extreme backpressure turbulence, which results in a loss of both velocity and static pressure in the main supply trunk. The mfg'ers need to re-engineer the distance from the heat exchangers and design effective transitions to the intake area of the evaporator coils.

Additionally, the return air intake should be at the ceiling level, in order to properly heat load the evaporator coil. Old gravity flow supply registers should be converted to diffusers, in order to achieve the proper air throw across the room.

To achieve maximum airflow efficiency, --the supply air and return air ductwork must be properly sized, along with oversizing the filter grille areas.

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The North Country Oil furnace A/C or heat pump scenario:

Any good Tech should already know what I am going to illustrate here; this is for Homeowners & any who can use the least costly way to deal with this too common a problem in the cold North Country.

We are moving into the cooling season; however, any changes in equipment should consider how every component matches with optimal airflow efficiencies.

My lowest cost solution to the cold climate oversized Oil furnace with a small tonnage A/C evaporator coil which requires nearly half the airflow as heating:

I ran a check on my late brother’s home & the summer cooling heatload is about 14,000-BTUH.

The original scenario, had much less airflow than required for 1.5T cooling; its 2-T A-Coil wouldn’t flow 1150-cfm for heating

I did a lot of other figuring; 45,000-BTUH output should heat that small single story home.

However, with the 140,000-BTUH input, 112,000 output Oil furnace installed; the nozzle size can be dropped from one gal an hour (we’ll use 139,000-BTUH input) to .75 @100-psi, the BTUH drops to 103,500 input, this furnace tested at .74% efficiency; *103,000 = 76,590-BTUH.

Using a 90F heating temperature rise, which Thermo Pride can stand; (90*1.06 here) 76,590 / 95.4F is 803-cfm.

Therefore, the 2-Ton A-Coil will handle the CFM; mounted +6 inches above the furnace, it has the flow capacity to work okay in both heating & cooling modes.

With a third HP belt-drive motor, you could simply adjust the RPM down by turning the adjustable motor pulley out enough to get to 700 or 600-CFM for the 1.5-Ton A/C.

The other solution is to install a multiple speed direct drive motor with the fan relay energizing the cooling speed tap.

This rather common situation in cold climates seems not to be properly addressed my Techs, & the HO does not know why things don't work well.

We should all work to improve efficient use of high cost energy ... so America & everyone wins. More proofs in below Article to get  airflow right.
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Why HVAC Systems are Less Efficient than You May Think

MAY 4, 2011 2:45 PM, BY ROB 'DOC' FALKE

We pulled test data from over 20 systems from our CommonCents™ database. This is an online testing and diagnostic software that NCI members use to collect and analyze information and present their findings to their customers. These were systems that had complied with his program’s energy standards and all had received substantial incentive payments. Here’s what we found:

• The average operating efficiency was 63% of equipment rated capacity at the time of the test.

• The average total external static pressure was operating at .86-in. of pressure with an average maximum fan rated pressure of .57-in.

• The system delivered airflow at the supply registers averaged 261 CFM per ton at registers (400-cfm per/ton is normal airflow).

http://link.contractingbusiness.com/u.d?U4Gp0d4hVVSpWIc7C7xs=41

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Required fan motor HP varies as to the cube of the rpm blower speed.

Also, at 700-rpm & .2" SP for heating my Thermo Pride OL 11 with its belt-drive quarter HP motor is supposed deliver 1200-CFM (mine does not);  add a cooling coil, & at .5 SP it will deliver only 400-CFM.

Keeping the total static pressure as low as possible and within mfg'ers ESP requirements for air conditioning is the first requirement in an efficient system design.

BTW, what is the average pressure drop across the new +90 high efficiency furnace condensers? That pressure drop should be published by all of the companies!
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My Scan of My ThermoPride OL 11 Graphed Blower-Curve-Chart
Thermopride OL 11 Graph ipg image - Thank you Dave Staso, CA. for the better expandable image!
"After it loads Right click "Show Original Images" - Move cursor arrow over graph - Click + when 'over graph' for expanded image," then print on the highest quality setting.

Therefore, every manufacturer should furnish blower line curve charts with their units and put them on the Internet for service tech's to download and print. A blower curve graph chart, for discerning the variables of ol furnace belt drive blowers. 

Observe how easy it is to fall below the required CFM with a quarter horse blower belt drive motor that was standard with 112,000 btuh output oil furnaces. Measuring the static pressure of the duct system & using an anemometer to check atual airflow is a must! The Thermo Pride OL 11 requires 1164-CFM of airflow to keep temp rise within 90-F.

Required fan motor HP varies as to the cube of the rpm blower speed.

Also, at 700-rpm & .2" SP for heating my Thermo Pride OL 11 with its quarter Hp motor will deliver 1200-CFM;  add a cooling coil, & at .5 SP it will deliver only 400-CFM.

Keeping the total static pressure as low as possible and within mfg'ers ESP requirements for air conditioning is the first requirement in an efficient system design.

BTW, what is the average pressure drop across the new +90 high efficiency furnace condensers? That pressure drop should be published by all of the companies!

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Every manufacturer should furnish blower curve charts with their units and also put them on the Internet for service tech's to download and print. Also, air conditioning codes should be updated in respect to proper sizing of the duct work which must include all the pressure inducing factors when sizing the supply and return ducts. Also, illustrate best furnace to evaporator coil transitions, especially on oil furnaces!  You should always keep the ESP to 0.5" or mfg'ers listing.

Also, air conditioning codes should be updated in respect to proper sizing of the ductwork, which must include all the pressure inducing factors when sizing the supply and return duct systems.

 
(Air Conditioning Systems) Typical Static Pressure difference before the fan to after the coil in existing installations averaged 0.54 inches of water column (134 Pa). Darrell U.

On an upflow furnace, External Static Pressure is measured before the E-Coil to determine your  the mfg'ers ESP Ratings.

Therefore, every manufacturer should furnish blower line curve charts with their units and put them on the Internet for service tech's to download and print. A true graph chart, worthy of printing and discerning the variables of belt drive blowers. Observe how easy it is to fall below the required CFM with a quarter horse blower belt drive motor that was standard with 112,000 btuh output oil furnaces. Measuring the static pressure of the duct system is a must!

The design of the oil furnace with its ultra large heat exchanger coming to near the top of the furnace and the blower set to the side of the furnace is an engineered airflow problem. The blower set to the side blows against the heat exchanger and the back of the furnace which blocks directional airflow velocity thus generating high initial velocity & static back pressures against the blower.

Most installers set the A-Coil directly on top of the furnace with no transitions resulting in another restriction and more blocking of directional velocity airflow and a huge leap in (ESP) static pressures'. Thermo pride states that the A-Coil must be at least 3" above the furnace. That might work for a small 1.5 or 2-ton A/C, but what about a 3 to 5-ton A/C's required airflow?

In my opinion, these low boy oil furnaces should be designed with space above the heat exchanger depending on the airflow requirements of the air conditioning application size to be used. There should also be a transition beginning at the top of the heat exchanger and transitioning to the intake area of the evaporator coil. This would greatly reduce the backpressure and improve airflow. The worst place to lose velocity and generate static back-pressure is below the evaporator coil. Where it needs the velocity and static pressures' is at the diffusers.

The low airflow probable cause is "an unbalanced airflow heatload through the evaporator coil, along with "back pressure and extreme turbulence," due to the evaporator coil being too close to the very large oil furnace heat exchanger.

With the DX coil set perhaps illegally close to the heat exchanger thus causing an airflow restrictions and wicked turbulence, a few of the coil's circuits may be unevenly heatloaded. Since the liquid refrigerant is not completely evaporated it will cause the outlet line that the TXV sensor bulb is on to be too cold and the TEV will shut-down the refrigerant flow, which can greatly reduce the BTUH capacity of the DX coil and the entire system.

Additionally, the return air intake should be at the ceiling level, in order to properly heat load the evaporator coil. Old gravity flow supply registers should be converted to diffusers, in order to achieve the proper air throw across the room. To achieve maximum airflow efficiency, --the supply air and return air ductwork must be properly sized, along with oversizing the filter grille areas.

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One Performance Assessment research revealed:
Several recurring factors were found to account for the inadequate flows:

    * Return ducts and return grills were often undersized
    * Fans were set to medium rather than high speed for cooling operation
    * Filters and cooling coils were dirty with high flow resistance
    * Duct system static pressures were elevated due to circuitous runs, pinched ducts, turbulence, etc.
    * Larger outdoor units were installed without changing the indoor unit. (Wow!)
    * Devices had been added which increased system static pressures.

On piston refrigerant control systems, they may flood back liquid which could damage the compressor, unless the system is way under-charge. Thermo Pride could install airflow turning vanes just above the heat exchanger to funnel the air directly into the DX coil, instead of most of the airflow hitting the bottom of the DX's drain pan causing extreme back-pressure/turbulence and an imbalanced DX coil circuitry heatload!

Static regain explained: every time the velocity is reduced there is a conversion to static pressure. In this case, it not only loses all of the velocity airflow energy due to hitting the heat exchanger, furnace side walls, and evaporator drain pan, which also skyrockets static pressure between A-Coil & blower, greatly reducing the blower's ability to deliver the required CFM!

The required main trunk Supply Air velocity is lost between the heat exchanger and the evaporator drain pan, and therefore there is insufficient velocity and static pressure at the Supply Air diffusers to deliver the throw and requisite CFM!

Darrell Udelhoven 
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• Clean the furnace flue pipe, barometric damper and chimney base.
• Check the condition of the furnace heat exchanger.
• Use brushes and a vacuum cleaner to remove soot buildup from the heat exchanger cavities inside the furnace. Use extra long heat exchanger brushes of the correct diameter and a shop vac with a ten foot long & one inch diameter hose, to remove soot buildup from Thermo Pride OL11 heat exchanger cavities. These are difficult to reach in many oil furnaces, and it takes patience and perseverance to do a good job. (Extremely Important for safe performance and efficiency!)
• This is the best Thermo Pride instructions for cleaning soot from the oil heat-exchanger Go to Page 10 on pdf
  

• Oil Furnace Heat Exchanger Soot Cleanout

• Contractor's Servicing Oil Furnace's Sooted Heat Exchangers

"Getting it RIGHT, makes all the difference in the world."
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DISCLAIMER:
Any of the HVAC companies I list on any of my web pages have nothing to do with the information I post on any of my Web pages nor do I assume any responsibility for how anyone uses that information.
All HVAC/R work should always be done by a licensed Contractor! This information is only placed on these pages for your understanding & communication with contractors & techs.

This information is for the edification of contractors and techs. I am NOT liable for your screw-ups, you are liable for what you do! - Darrell Udelhoven

Darrell's Refrigeration Heating and Air Conditioning - Federal Refrigerant Licensed - Retired Licensed Contractor

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Darrell Udelhoven - udarrell
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Posted: 01/28/04; Edited: 05/04/11