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For one heating system to operate properly, the ductwork is a very important part of the duct distributing system. (Up to 75%)
Each manufacturer has strict requirements for what CFM has to pass to a coil (heat exchanger) and what ΔT of circulation air should be.
When these parameters are not met, the efficiency is not in up to par as well.
ASHRAE standards clearly show us what path we have to follow in a design of a duct distributing system.
Duct distributing system 1-5 stars:
One starThe one star rating features a poorly designed duct distributing system, and the most flexible duct usage.
During the coldest winter days the equipment usually gets overheated. There is no comfort level at all in the house. There will be no sufficient return, and wheezing noises will be constantly heard. If there is a second floor there will be no cooling conditions on either room facing south. Many times the home owner will close the lower locating register, trying to push the air towards the upper floor. That leads to more critical working conditions than before and can shorten the equipment’s lifespan.
After the math:
It is very costly to fix the problem when the house is occupied.
There is a big possibility for the heat exchanger to fail and a crack, which will leak carbon monoxide into the living space.
How to recognize the bad design:
You are unable to keep your hand longer than 3-5 seconds on the hottest possible location.
The equipment door is slamming into the unit due to the lack of return air. Hot air is coming out from the register into the mechanical room.
Always very cheap prices.
Sheet metal not available at fabrication shop.
We are not able to beat that bid. Two StarA sometimes nice looking job when examining the setup on the mechanical equipment. Vibration pads are sometimes used. Sleeves are installed on the supply and return ducts in order to reduce the noise.
If present, the mechanical noise can be fixed, and is not too bad prior to this. Our two star certificate usually involves a turbulent noise, as well as high energy bills and frequent service calls. This type of installation usually has a system that is much shorter than what the manufacturer’s warranty calls for.
However, replacing the unit is not the answer. This system also often has insufficient comfort during summer months. The thermostat is set to low temperatures and is not able to keep that temperature. There is a 60% chance for the compressor to fail during the 5th or 7th year. |
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Three StarThe job looks like a regular installation with returns everywhere. There is usually one per room. Many times and upward or downward facing opening is present, which interferes with the system’s ability to work properly. Improper starting with the right fittings from the plenum is usual. Improper fittings are used for connections to the main trunk line, and banging noises sometimes come from the mechanical room when the unit starts and stops. Improper attachment on the return duct to the unit for houses (bigger than 2300 sq. ft. ) cause from 30% to 50% higher heating bills.
In our opinion, the three star certificate is the worst. The reason for that is because the unit operates to its limit and the system is usually oversized. Our research for the last seven years has led us to a conclusion that 60% to 70% of the houses have a three star system on site. Once again, we are seeing manufacturer recommendations for ∆T F degree on return and supply air not being met. Simply put, this means that instead of an efficiency of 92%, the equipment is performing at no more than 70% efficiency, which could be an overpayment of somewhere between $60,000 to 100-$110,000 for the life of the house. (Approximately 60 years). |
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Four starA Four star system is considered under Geothermal house certificate to cover up to 80% of the return air that the equipment needs. A forced air system will have no problem to work fine at this level. There is a small mistake on return, but it is nothing major like the one star certificate. Some return boxes do not have the deepness required for air to pass. Usually, the size of the duct coming in and out is the same. A total of two or three returns are present in this system.
The heating bill is usually higher by 10 to 15%, but the equipment has no problems covering this because is oversize between 15 to 40 % on the top on the heat load.
The estimated overpayment energy bills for the life of the house (60 years) is vary from $15,000 to $30,000. Only a very trained eye can discover that kind of mistake in this kind of installation.
Geothermal technology will not perform well enough to give the home owner necessary energy savings, because payback period will not be in a satisfactory time frame. Five StarThe Geothermal house installs geothermal equipment and other forced air equipment only with five star systems. This system is performs perfectly because we use ASHRAE fundamentals and RSES recommendations. It usually takes time to implement that kind of distribution system, but that leads to a quality installation. The speed into the return duct is good and there are no sweesing noises. A return close to the equipment will lead to a chance of some type of noise, but the heating contractor will take that in consideration. There are many custom reducers, transitions and reverse elbows if the design and installation process requires them. All returns are taped into a return proper box and proper grill. There are custom built nineties with a large radius for the farthest supply registers. Proper connections are present on all individual branches following as well as on the air flow. Insulation in the inner site of the return ductwork must be placed in order to minimize the noise coming from the equipment itself. There will be no connections on the high site of the ductwork which will create turbulent flow. Proper connections on the return duct to the equipment will allow the home owner to use the highest efficient filtering system without restricting the flow whatsoever. This system has the ability to be adjusted in both winter and summer without any under-performance of the equipment.
The expected life of the equipment with five star system is 22to 30 years. After that the compressor as well as some other basic components can be replaced, and the GEO will be brand new again and ready to work for the next 25 years.
Any other forced air equipment with a five star system will have an expected life of about 17 to 20 years.
This is the only system that will give you the maximum performance of heat.
There is a much longer period of time when the geothermal system is a match with a 4 star and has a no payback period with 1 to 3 stat systems.
CONCLUSIONS:
With these standards we try to lay down a frame with requirements that will evaluate any current or future job.
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