| CONDENSER TEMP SPLITS | Is your AC 30 to 50% Oversized? - with Darrell Udelhoven - HVAC RETIRED - udarrell
|
We could
cut
residential heating and cooling equipment size in America by 30% to 50%
if
Contractor's would perform honest Manual J calculations and provided
full
credit for every load reducing element or detail they can when doing
the
calculation audit. Additionally, load reduction remedial actions should
be
provided as options toward further reducing Air Conditioning and
heating
equipment sizing.
Down sizing has many advantages; the existing duct system & air handler will function more efficiently helping to achieve the unit's nominal tonnage capacity with less than peak heatload conditions. That improves EER & SEER performance. Contractors' should use the equipment manufacturers blower data and the Manual D procedures to find the room cubic feet per minute (CFM) airflow values and then use published performance data to select the appropriate sized supply air outlet, type and size, for each room. There also should be a low resistance return air path for every room that has a supply outlet, door undercuts are borderline acceptable. Manual D procedures should be used to size all the duct runs, and systems should comply with ASHRAE standards; completely seal all runs located in an unconditioned space and insulate these runs to preferably R-8. Contractor's should Certify the work they have done, i.e., —measured all air flows, balanced the air distribution system and then used certified protocols to check and balance the refrigerant charge. After all the installation work has been done, the Operating Performance Standard Data of the operating System should be Certified by the contractor. This should Include the static pressure readings, CFM of the system airflow, air temperature rise across the condensing coils, and the entire performance data. Provide your customers with more than they paid for and you will have more business and solid referrals. Measuring Low Airflow
I normally would measure the airflow with a flow hood, also called a capture hood. You should normally have around 400 CFM (Cubic Feet per Minute) per ton of cooling. Half of the systems I measure have [a mere] 200 CFM per ton, OR LESS. This will be aggravated by a dirty air filter, Some Restrictive high efficiency air filter's or grilles closed in rooms that you are not using. Normally, do not turn the thermostat down below 70º [74º 76º -better] degrees. says A/C Tech guru, 'Stretch' First,
before doing
anything
else check the sizing, and thoroughly seal and properly insulate all
the ductwork!
|
||||||||||||||||||||||||||||||||||||||||||||||
|
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 Toward Optimal Occupant Comfort
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!
| EER |
7
EER or less |
8
EER |
9
EER |
10
EER |
12
EER |
13
EER |
| 'Max' condenser air temp 'delta-T' |
30 |
27 |
24 |
15
to 25 |
14
to 24 |
ave.
less |
| Max
temp drop 'across' E-Coil |
20 |
22 |
24 |
26 |
ave.
more |
ave.
more |
| 'Max' SA/Return Entering Air 'Delta-T' |
35 |
32 |
29 |
27 |
ave.
less |
ave.
less |
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!
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 toward adequate 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.
If all contractor's would do the above, coupled with installing equipment sized according Manual J loads (with no safety factor), along with Manual S selection procedures, comfort would go up, humidity control would improve, and installation and operating costs would be much lower.Especially
if your system is oversized or there are a lot of low AC load days use
an adjustable differential room TH.
TH
Differential: Differential is defined as
the difference between the cut-in and cut-out
points as
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 air. Motor
heat is a factor to be dealt with, perhaps more so on the smaller units.
If you do not know whether the metering device is a TXV or orifice?Normally plus or minus 3-degrees is acceptable for Subcooling, i.e., SC Target of 12 +/- 3 = 15 or 9-F SC.
Hook up your manifold gauges, block off considerable condenser air intake. If the suction pressure starts rising, you have a piston, or a cap tube.
If only the high side goes up, you have a TXV.
If it is a piston, get the CFM airflow correct first, then use the superheat method to charge it.
If it is a TXV, subcooling is the way to charge it, but check the Superheat to verify the TXV is holding within specs.
Do your own figuring based on this formula. Get the Motor Power Factors (PF) of the compressor and fan motor from the manufacturers.
CONDENSER TEMP-SPLITS 12-SEER units - Comfortmaker® | Heil® | Temp Star® - used 0.88 Motor Power Factors
1.5-Ton 18,000 21-F Split Cond. CFM 1400 WATTS 1536 1.5-Ton is from actual published DATA - ARI Rating Conditionshttp://www.udarrell.com/air_return_latent_condenser_split.jpg IE Browser's
2-Ton 24,800 23-F T.-Split Cond. CFM 1400 WATTS 2659
2.5-T 30,200 20-F Temp-S Cond. CFM 2000 WATTS 3404
3-Ton 35,600 17-F Temp-S Cond. CFM 2800 WATTS 4107
3.5 T 42,500 19-F Temp-S Cond. CFM 2800 WATTS 4554
4-Ton 48,500 18.5-F Temp-S Cond. CFM 3400 WATTS 4761
5-Ton 59,000 23-F Temp-S Cond. CFM 3400 WATTS 6969
The new Goodman 13-SEER 1.5-Ton Condenser, 2-Ton Evaporator:
At 675-cfm 450-per/ton cooling | 85-F ODB | 63-IWB | 52% RH | 20-F ID Delta T | 18,600-Btuh
201-psig 100-F = 15-F cond. temp split - smaller capacity compressor to larger coil areas | 80-psig suction
=================================================================
The
Base Spec sheets
12-SEER
part no. 421 41 33301 03, Feb 2001. These are the Comfortmaker®
units, which are nearly identical to Heil® units. I used
the first rating on each tonnage class. While the "Performance Cooling
Data" is listed at a 95-F outside ambient temperature, you
can adjust the indoor airflow to get the Nominal BTUH Rating at the
customer's normal indoor stat' temp' setting, and the most outside
temperature/degree
operating hours.
Take
the "listed watts" of the compressor and Condenser fan and multiply
that wattage by 0.85 X's 3.413
to get the BTUH heat additive of the
motor then add the listed BTUH of the condenser to it, and then divide
by the condenser fan's CFM.
By
using
the various units' "base specification sheet data" from the
dealer,
you can determine if it is operating near its BTUH capacity rating. Some packaged units run a very
high condenser discharge CFM airflow
Have
a manual J heat-load
calc done, and in humid climates, consider slightly undersizing a
replacement condenser.
If you have an older furnace, there may not be enough airflow through the evaporator coil.
Have all of the ductwork, diffusers, return-air grilles and filter areas checked and properly sized, the ductwork must be properly sealed.
In cold climate, consider replacing the furnace with a new high efficiency condenser furnace.
Then
replace the central A/C
system, Go for a scroll
compressor & a TXV
refrigerant control on the evaporator.
By slightly undersizing the condenser and making certain you have an
optimal and balanced heatload on the cooling coil during normal
run-time conditions, —the unit will have a much greater BTU/hr heat
transfer output during average run-time conditions!
Air
Temperature Drop
Through Evaporator Coil (1987 Period)
Indoor
temperature
and humidity load variations graph.
Refrigeration
&
Air-Conditioning (ARI) Second Edition,
Page 624, ©
1987
Getting
it right makes all the difference in the world.
============================
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 what you do,
you are liable for what you do! - Darrell Udelhoven
|
Please write me if you have anything you'd like to contribute! - Darrell |
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Posted:
10/16/03; Edited: 06/24/08