Air Conditioning Total Heat Enthalpy - Latent Heat Removal - 
What is the most Affordable Path to the "Human Comfort Zone" Goal?

with Darrell Udelhoven

Design Engineering objectives should be focused towards achieving the most efficient and effective means toward  a conditioned space that is within the "Human Comfort Zone, " and at an affordable investment 'payback' period."
 

Summer Comfort Zone.

Relative Humidity

Maximum Comfortable Temperature

Minimum Comfortable Temperature

60%

78.5oF

 72.5oF

50%

79oF 

73oF

40%

79.5oF

  73.5oF

30%

80oF

74oF


The above comfort zone was found to be acceptable to 90% of test subjects drawn from a range of age groups and genders, with work and life-styles involving varying levels of activity and clothing. An air conditioning system that establishes and maintains indoor conditions within this zone will provide thermal comfort. It will produce a neutral sensation, occupants will feel neither too hot nor too cold. Above chart and findings From: Home Energy Magazine Online September/October 1996) Sizing Air Conditioners: If Bigger Is Not Better, What Is?  by John Proctor and Peggy Albright
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If you over pay for over capacity equipment, --you will be paying more every month and will not be as comfortable as you would sizing it right to also achieve the appropriate humidity levels!

When a typical HVAC contractor quotes the efficiency of the Air Conditioning equipment's SEER & Btu/hr, and leads you to believe the new equipment will automatically deliver that SEER efficiency & Btu/hr rating, think again. Typically, --installed equipment only operates at 55% to 70% of rated capacity. Oversized equipment is the worst combination there is because the duct system airflow and heatload on the cooling coil are often way off what is required!


It is important to understand that "equipment ratings are only the 'potential efficiency' of that component of the system under perfect conditions." Over half of the system’s efficiency depends on correct equipment sizing run-time, on the duct system sizing, i.e., on the quality of the complete field-installation!


What you want & need is right sized equipment operating at its optimal ratings within varying conditions, for your optimal comfort and savings.


When considering initial cost and pay-back period, -- is there too much emphasis on ultra-high seer-ratings when considering the most effective engineering and marketing path towards achieving the most affordable "Human Comfort Zone" Goals?

"A lower cubic feet per minute (cfm) airflow when air is at 50% Relative Humidity or below, will condense and absorb a larger portion of the air's latent heat." With a properly sized system coupled with a properly adjusted TXV the system will better adjust to varying conditions.

I believe that optimal efficiencies under variable latent heat loads could be effectively achieved through the use of computerized engineering.

The total latent and sensible evaporator heat load needs to be optimized at your normal operating conditions. This will also optimize the condenser's heat-load.
It is best to have the supply air and return air near the ceiling where the warmest air is located.

Come on engineers, consumers need a wholly variable system to achieve optimal efficiency performance when functioning in variable humidity conditions. HVAC company engineers can do it, therefore the companies need to get them on the market in the proper climate zone areas and at reasonable price levels.
This computerized control system AC would have to be sized to the combined latent and sensible heat load targets (78ºF/50RH) and the cubic foot volume of air changes that we would like per hour. This would need to be performed accurately to achieve the requisite run time and our combined comfort zone and unit efficiency goals.
Air Temperature Drop through Evaporator Coil
  Air Temp Drop - Evaporator

 


Air Temperature Drop through Evaporator Coil (1987 Period)
Indoor temperature and humidity load variations graph.
Refrigeration & Air-Conditioning (ARI) Second Edition,
Page 624, © 1987

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



Air Latent Retuirn Split

Page 618, Refrigeration & Air-Conditioning (ARI) Second Edition, C 1987
Those lower SEER units had higher condenser splits than 12-SEER and higher units.
Sorry, I defiled the graph, 90-db outdoor, 80-db indoors with 67 wet bulb or 50% RH represents the condenser splits shown above graph. Graph: 80-DB & 80-WB line-intersect is 100% Relative Humidity.

A graphic illustration of how the latent heat capacity of the DX coil "increases with the increase in room relative humidity, and the total condenser load also increases proportionally. Total system capacity to remove heat in Btu/hr increases above the manufactures' ratings which are at 50% RH when the Relative Humidity is much higher. Total Heat (Enthalpy) is the total heat content of the air and water vapor mixture. It is the sum of both sensible and latent values, expressed in Btu per pound of air.

With "a properly sized system," thoroughly sealed duct system, and proper evaporator heatload airflow you will have consistent optimal nominal heat absorption removal capacity, coupled with requisite longer run-time cycles. I believe that optimal efficiencies by using a variable ratio latent/sensible heat loading, could be effectively achieved through the use of computerized system control components.

New Efficiency Component Technologies
Multi Split Air Conditioning

This operates in much the same way as the 'split' system. The 'Multi-split' system enables a number of indoor units to be individually controlled from a single outdoor condenser.

VRF Systems

Variable Refrigerant Flow systems are the most modern and sophisticated development of the 'split' systems.

EXVs - Electronic Expansion Valves - Control system for heat pump/air-conditioning system for improved cyclic performance

The microprocessor-based control system optimizes efficiency of the ON/OFF cycle by shutting the expansion valve fully closed at the beginning of each OFF cycle to maintain system pressure differential. At the beginning of each ON cycle the expansion valve is opened to an initial larger than average of three openings to allow the system to quickly reach steady state operating levels. Thereafter, the valve opening is reduced to an average of the last three steady state settings. After a predetermined time, control of the valve opening is passed to an adaptive control algorithm which adjusts the valve setting for optimized performance during steady state.

The Digital Scroll compressor delivers excellent seasonal energy efficiency (SEER). The SEER advantage becomes even greater for a tandem configuration. When both compressors are operating, the example system has a high EER of 11.3 and at 50% capacity, when only one compressor is operating at full load, the compressor operates at a high EER of 11.3 too. The operating range for a single Digital Scroll is from 10% to 100% and in a tandem configuration is from 5% to 100%. Wide operating range ensures fewer start-stops on the compressor. Fewer start-stops ensure higher system performance. Coupled with two speed condenser fan motors!

S - Net System

S- Net is the Samsung proprietary "system monitoring" program. The software can be used to monitor the functioning as well as the health of the system - pressures and temperatures at all key points in the air-conditioning system. Each indoor unit can now be controlled remotely through this software. S - Net is available in both RS232 protocol and also TCP/IP. It is now easy to monitor the health of an air-conditioning system through the Internet, from a remote monitoring site. Figure 7 shows the S- Net cycle monitoring screen. Figure 8 shows the S- Net remote controlling screen.

 INTRODUCTION TO TOTAL COOLING PERFORMANCE
Mr. Slim Split-System-Ductless Air Conditioning  Unique Quite Efficiency Features ?
  May be better than window units?

how installing a 3-ton system can become a 1.5-ton system of actual delivered cooling (SURPRISE!):
http://epb1.lbl.gov/residential/cool.html 

It is better to slightly undersize than to over size, as proper sizing results in gains in run time and latent moisture removal. Short-cycling wastes energy in obvious ways, start-up uses extra power, it also takes at least 5 minutes for the unit to reach its cooling capacity.

These are major Problems with most Manufacture's Ratings' Data

Air conditioners selected based on standard indoor conditions of 80°F Dry Bulb (DB) with 50% relative humidity (which is the standard ARI capacity rating condition) will be incorrectly sized for 76°F Dry Bulb. Unfortunately, many of the major manufacturers' provide information only at 80°F. It would be a great improvement if the manufacturers' provided tables that presented the sensible and latent capacities at 76°F Dry Bulb for a variety of indoor humidities.


There is more to the "System Btu/hr Capacity Ratings in respect to the conditioned air space," than meets the eye. "It all depends on what is included or excluded in the capacity ratings in respect to motor heat Btu/hr that does nothing to reduce the total heatload of the conditioned space air." Motor heat is a factor to be dealt with, perhaps more so on the smaller units. I will list the formulas and illustrate the impact of the motor heat from the three motor sources.

Some possible Factors to consider when figuring the actual conditioned space Sensible Heat-Load to be removed and the variable Latent Heat-Load to be removed.

You can use the high-side (SCT) Saturation Condensing Temperature on your manifold gauge's dial, minus the outdoors-ambient Temperature; the difference gives you the condenser temp-rise or temp/split. There is NO excuse for not utilizing this important diagnostic check. Always use an accurate volt meter and amprobe to make sure you are not overloading the compressor's Wattage Service Factor and check the compressor discharge line to see that it is under 225-F. 

First, figure the 'rated' gross capacity of the condensing unit. To determine the "Gross BTUH Heat Ejection" of the outdoor condenser: New Data = Let's take the total 'Watts' from the data sheets on an 17,500-Net-BTUH Heil condenser with a 2-ton DX evaporator coil with a TEV/TXV refrigerant control.

Add the condenser motor heat: 1591-watts X's my low Power Factor of 0.90= 1432 X's 3.413= motor heat additive of 4887-BTUH + 17,500-BTUH = 22,387-BTUH Gross condenser heat ejection.
22,387 / 1400-CFM of condenser fan = 16-F X's 1.08 = 17.3-F Rated Temp rise split off the condenser. A properly operating matched system should be within 10% of the condenser's gross temperature rise. 

Take the "listed watts" of the compressor and Condenser fan and multiply that wattage by the Power Factor, they used to use 0.90, then times 3.413 to get the BTUH heat additive of the motor, then add the listed BTUH of the condenser to that figure, and then divide by the condenser's CFM. Multiply that figure by 1.08 to get the temperature rise.

Brother Don’s 18,400-Btu/hr, I used 17,500-Btu/hr rated 13-SEER Heil central A/C unit. Tweo ton Evaporator with TXV & Scroll compressor

1.08 *Xs 10-F split = 10.8 X 1400-cfm = 15,120-Btu/hr (outdoor) condenser, minus 4887-Btu/hr motor heat = 10,233-net-Btu/hr Xs .76 sensible = 7,777 sensible .24 X 10,233 or 2,456 latent heat transfer.

7777/16-F indoor split = a mere 486-cfm | I want at least 750-cfm when supply and returns are at floor level!

New 13-SEER 1.5-Ton Goodman,  Model GSC 13 0 181A  Match. -° From Goodman's Expanded Performance Data
85°F (OAT) Outdoor Ambient Temperature; 80 IDB; 71 IWB / 64% RH;  675-cfm; 212 psig - 105.5°F SCT minus 85°F OAT = "Condenser split 20.5-F;"  SA/RA delta T (split) 20°F.

New 13-SEER Goodman  Model GSC 13 0 181A  Match. - From Goodman's Expanded Performance Data
At the ARI Rating: 95 OAT; 80 IDB; 67 IWB / 50% RH;  600-cfm; 229 psig - 113.32 SCT minus 95 OAT = Aprox 18.32 Condenser split ; 84 psig 50-F Coil Temp;  SA/RA delta T (split) 21-F.

New 13-SEER Goodman  Model GSC 13 0 181A  Match.
At 85-F Outdoor Ambient Temp (OAT); (75 IDB; 67 IWB;) 525-cfm; 193 psig = 99 SCT minus 85 = [Condenser Split 14-F;] SA/RA delta T at 17-F

For the uninitiated, Delta-T is the difference between the air temperature entering and leaving the outdoor AC condensing unit. This is a good diagnostic check because it measures the latent heat of condensation as well as the sensible heat absorbed by the vaporizing refrigerant in the indoor evaporator coil. I'm betting when you find out approximately how many BTUH that the AC system is actually transferring outside, you may be shocked by how far it is below its BTUH rating.

His condenser usually has a 10-F temp delta T, the evaporator appears to be under CFM heat-loaded or, it has an unbalanced heatload on the DX coil's circuitry allowing liquid refrigerant in the return line causing the TXV sensing bulb to reduce the refrigerant flow thus reducing the DX coil's heat absorption capacity. 

The probable cause is "an unbalanced airflow/heatload through the evaporator coil. "I have a Thermo Pride OL 11 oil furnace. Those oil furnaces have a very large round heat exchanger that goes to near the top of the furnace, --due to a low basement ceiling the DX coil sets perhaps illegally close to the heat exchanger causing a few of the coil's circuits to be under heatloaded. Since the liquid refrigerant is not completely evaporated it will cause the outlet line that the TEV sensor bulb is on to be too cold and the TEV will shut-down the flow, which greatly reduces the BTUH capacity of the DX coil and the system. On piston refrigerant control systems, they may flood back liquid which could damage the compressor, unless the system is way under-charged. 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 turbulence back-pressure and an imbalanced DX coil circuitry heatload!

The chart split listed below is at Condenser Design conditions: Indoor Return Air 80-F dry bulb 67-F Wet Bulb or 50% Relative Humidity as you go up to 99% RH the condenser split could increase by up to 6-F; down as much as 4-F at a low humidity of 55-F Wet Bulb.
Do your own figuring based on this formula. Motor BTU/hr additive = Watts X's PF x's 3.413 for Btu/Watts additive added to rated BTUH, divided by condenser fan CFM X's 1.08 =  condenser Temp-Split. Get the Motor Power Factors (PF) of the compressor and fan motor from the manufacturers. Some of the temp-split figures need correcting, will do ASAP. Some Splits rounded.
CONDENSER TEMP-SPLITS - Comfortmaker® 12-SEER units - used 0.90 Motor Power Factor - ARI Rating Conditions
1.5 T  17,500  17.5-F Split        Cond. CFM 1400 WATTS 1591x.90=1432x3.413=4,887+17500=22,389/1400=15.9x1.08=17.5
2-Ton  24,000  23-F Temp-S  Cond. CFM 1400 WATTS 2067x.90=1860x3.413=6349+24000=30349/1400=21.7x1.08=23.4
2.5-T  30,000  21-F Temp-S   Cond. CFM 2000 WATTS 2778x.90= 2500=8533+30000=38533/19.2x1.08=20.8
3-Ton  35,600  14.8-F T-Sp    Cond. CFM 2800 WATTS 3096x.90= 2786+35600=38386/2800=13.7x1.08=14.8
3.5 T  42,500  17.6-F T-Sp     Cond. CFM 2800 WATTS 3578x.90=3220+42500=45720/2800=16.3x1.08=17.6
4-Ton  48,500  19.5-F Split     Cond. CFM 3400 WATTS 4174x.90=3756.6x3.413=12821+48500=61321/3400=18x1.08=19.5
5-Ton  59,000  23-F Temp-S  Cond. CFM 3400 WATTS 5043x.90=4539x3.413=15,490+59000=74490/3400=21.9

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A modern 2-ton 13-seer system would produce around .70 of per-ton or 8,400-Btu/hr, however at 70% Relative Humidity its capacity would increase to around 1.1 per-ton or 13,200-Btu/hr or over half of the 2-tons would be used for the latent heat-load. "That is around a 36% increase in latent capacity" and a 36% reduction in sensible capacity, --due to a higher humidity.

There are four main factors to humidity control. These are related to equipment selection and installation and the effects of the performance of the four equipment factors. The Four Factors are: evaporator coil selection, airflow, refrigerant control device, and superheat setting of the refrigerant cycle.

Proper duct sizing and location is important. Most older homes need reduced ambient (outside) air infiltration and more effective use of vapor barriers, coupled with adequate insulation. Windows and doors are special areas to work on. My upstairs windows around the pulley wheels for the weights, allowed air to blow through almost unrestricted from the attic area both winter and summer.

Air Flow
When it comes to airflow, the laws of physics apply. Air follows the line of least resistance. So many of the duct systems are poorly designed that ductwork problems can seriously curtail proper system performance. These factors usually show up in uneven temperatures through the conditioned area. In addition, airflow across the cooling coil can affect humidity removal. Too much air will result in poor dehumidification. Too little air can cause the registers to sweat. The right amount of air is usually between 325 CFM and 400 CFM per ton. Lower airflow will produce increased humidity removal, but compromises sensible heat removal. Finding the right air flow and run time balance can eliminate most of the comfort zone humidity problems.
My scan of my doctored Thermopride OL 11 Blower Curve Chart:
http://www.udarrell.com/Blower_Curve_Graph.tif

Condensation forming on supply air diffusers or registers is caused by insufficient airflow through the evaporator coil and the individual ducts that may be sweating due to lack of insulation.
Refrigerant Control Device
The device used to make a cooling coil evaporate refrigerant and thus absorb senile heat and latent heat of humidity is called a Thermostatic Expansion Valve refrigerant control. The most effective refrigerant metering control in this application is "a balanced port (TEV/TXV) expansion valve." The expansion valve provides consistent performance over a wide range of conditions that exist in any home. Without an expansion valve the entire system performance is compromised. Adding an expansion valve to an existing system can often improve performance, reduce operating costs, and extend the life of the overall system.

Superheat

One factor that is often overlooked in trying to increase humidity removal is the the superheat of the suction gas. Superheat can often be out of design conditions and the system seems to work fine. A five degrees warmer coil temperature can reduce humidity removal by 20% or more. Correct TXV adjusted superheat for optimal latent removal should be between 5-F and 7-F degrees at the coil. The best time to adjust the superheat is on hot summer days, under normal load conditions 75-F indoors strive for 55-F degree discharge air or 20 + degree drop. (Use only TXV metering devices; that's a policy that would be helpful.)

If any of the above factors are not correct you can expect that humidity problems will occur. Other factors can affect the humidity levels. The way the house was built — the number of people that live there and the life style of the occupants. The correction of humidity problems in any residence may be accomplished by applying the above factors. This is why it is essential that you find a company that you can trust to solve your humidity problems. if neglected, humidity problems only get worse.

In my opinion all the components of air conditioning systems should be engineered and specially designed for the climate zone conditions where they will be shipped and used.

 In humid climate areas, the use of a dehumidistat and variable speed programmable indoor blower motors that use half the electricity of conventional motors could be used. Also, ask your Utility company about their "high efficiency Rebate Program," these programs can add to your energy cost savings.

Arid climates can use a higher temperature operating oversized coil, coupled with 450-cfm or more, per Btu/hr ton of cooling, -- cycling through the evaporator coil along with a lower rated btu/hr compressor to condenser ratio.

There ought to be a code requiring every manufacturer of an airhandler or furnace to provide capped taps ahead of the evaporator coil and ahead of the blower for easy static pressure testing access.

All air conditioning condenser manufacturers' should publish the CFM and normal temperature rise range across the condenser coil, so that the service tech's can measure the heat transferred from the evaporator coil. Most high efficiency units will have temperature degree rises between 18 and 25ºF. Older lower SEER condensers can have temperature rises up to 28 or more degrees.

Such temperature rise data provides a guide to the actual heat transfer by the evaporator coil to the outdoor condenser coil, and therefore also, whether the proper design amount of (cubic feet per minute)  CFM of indoor air/per ton of cooling Btu/hr, is passing through the heat absorbing -- cooling coil.

Most higher efficiency units are designed to operate at higher evaporator coil temperatures which results in less temperature drop, also the high outside and inside humidity levels will put a heavy latent heat-load on the evaporator coil will delay the conditioned area's temperature drop.

You may also have too much outside air infiltration into your home, check it out and reduce it, because warmer high humidity air will overload the evaporator coil with latent heat removal with the result being little if any reduction in humidity levels and no lowering of the actual sensible temperature readings in the conditioned areas.

In high humidity climates everything in the home is loaded with the latent heat of moisture. Humid air contains a lot of heat-loaded vapor. Some moisture is airborne but most of it resides or hides in the bricks, wooden furniture, carpeting, walls, and the concrete floors we walk on, etc. Dish washers, clothes washers and taking hot showers, etc., all add a lot of moisture to the air and to home materials.
This latent moisture in the conditioned area is vaporizing in the air, and as it is being conditioned it gives up its latent heat to the evaporator coil's liquid refrigerant causing it to boil into the heat absorbing refrigerant vapor. That heat-loaded vapor is then sucked back to the compressor where it is compressed into a high temperature gas in the condenser coils, where the outside air cooler outside air cools it below its condensing temperature point causing the vapor to condense into a liquid.

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I do NOT assume any responsibility for how anyone uses the information on my Web pages.
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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Posted: 05/25/05; Revised 08/30/06