Confused about Terms (Variable Speed, multi-stage, etc)
I thought to be a more educated consumer I would pose the some questions to this august crowd. They are as follows:
Can someone explain the difference/benefits of a variable speed vs a multi-speed vs dual speed AH blower motor?
What is meant by multi-stage outside unit vs a single stage outside unit?
If the 2H/2C thermostat doesn't control the speed of the Variable/Multi/Dual speed AH how is it controlled?
How do manufacturers get a higher SEER rating by mating certain outside units with certain coils and furnaces?
All this terminology makes it hard for the consumer to compare apples to apples when it comes to making an informed buying decision.
Inquiring minds would like to know ...
I would think that many other would like to know these things. I think this would make a good sticky ...
Thanks for the clarifications ....
(1) True variable speed motors provide a much more consistent level of dehumidification (summer) and delta T (winter). They provide better IAQ by running @ very low speed during off cyles. Also by running during off cycles they keep the air "mixed" which reduces stratification and hot and cold spots in the home. They are also very quiet. Dual speed motors do not offer the flexibility, consistency, IAQ improvements, or quiet operation.
(2) Multiple speed outdoor units offer reduced capacity during reduced demand which in turn offers reduced utility bills. They can be dual compressor, single compressor w/2 speeds, or I think only one manufacturer currently offers a true variable speed D.C. compressor. Along with benefits in lowered utilities, you get quieter operation both from the compressor and the variable speed outdoor fan motor. The multi speed ODU's also control humidity and delta T's better than single speed units.
(3) Variable speed systems are controlled by the circuit boards in the Air handler/Furnace and outdoor unit, not by the thermostat.
(4) Matching equipment rates a higher seer from the manufacturers due to many variables. Some of which are refrigerant flow, refrigerant capacity, rate of flow, coil surface areas, air flow, resistance to air flow (fins per inch), IAQ, etc.
Hope this helps. I'm sure the others will chime in with many more answers to your questions.
"Surprised ?! If I woke up tomorrow with my head sewn to the carpet, I wouldn't be more surprised."
Thanks for the info. Now I'll try to apply this new info to the quote I got for a new HVAC system.
Thanks again ....
As Ira explained there are variable speed (VS) blowers for the indoor units and multi capacity units for outdoor sections and gas furnaces.
VS blowers allow for greater comfort as they change the amount of air flow to meet the different capacities of the gas furnace, heat pump or A/C. Multi speed blowers are simply a blower that has multiple speeds, but the installer must select one for cooling and one for heating when installing the system. Then, whether it is cooling or heating, that will determine the air flow.
VS blowers are able to maintain the amount of air flow. If the air filter becomes a little clogged with dirt causing more resistance to air flow, a VS blower will ramp up its speed to maintain the CFM. This is good for your equipment by maintaining the proper air flow, but should not be viewed as a fix for poor/undersized duct work that does not flow air sufficiently.
VS blowers have become more prevalent as multi capacity systems have become more widely available. With a two stage heat pump, the air flow requirements between the two stages is dramatically different. When the t-stat calls for 1st stage the circuit board with the blower sets the blower for the lower air flow needed with first stage. When it moves up to second stage the air flow increases too. With certain t-stats the blower will be slowed further when there is a call for de-humidification. Cant readily do that with a multi speed blower.
The other benefit of VS blowers is with the proper duct system that can move the air without excessive resistance, the blower will use less electricity.
Thanks for the further input. If I may, the system I'm looking at is a Goodman ARI Ref# 1047183. I gather the system is using a VS condensing gas furnace (95%) and a SSX160481A Outdoor Unit. I was trying to understand all the jargon and figure what type of system I was getting.
The outside unit has a 16 SEER rating. I was trying to figure out how the VS furnace was going to help with the humidity of the Texas summers. We don't use much heat here in the winter. However, I'm all for a reduced electric bill as it gets prety high in the summer. The new unit will be replacing a 9 SEER Goodman. It has been a good unit but the install was marginal at best.
Can you explain how this system will operate in the cooling as well as the heating mode?
You are getting the top efficiency gas furnace that does not need to provide much heat. I would think that a lower cost option, such as an 80%, would be worth considering. With the savings from that you could then opt for a two stage outdoor unit that will do much more to help with the high humidity you have. Goodman does not offer the two stage systems in a 4 ton size but there are many manufacturers that do.
Originally Posted by timby
Not knowing your gas and electric rates I am guessing, but a heat pump instead of gas furnace with a/c might be another way to reduce costs in one area so that you can get some additional features that will provide increased comfort and maybe help with the long term utility costs. Heat pumps can heat your home more economically than the most efficient gas furnace - depending on your utility costs.
As for the heat pump, electricity is very high here. My gas bill in the winter is seldom over $100 per month. That's with a gas furnace, range, DHW, and dryer. So I don't think a heatpump would be a very good option.
I realize that Goodman doesn't offer a 2 stage outdoor unit however, the prices quoted for Trane and Lenox systems were much higher. I get a full 16 SEER unit for less than a 14 SEER Trane. The Lenox system was the same SEER rating but a 80% furnace.
Like I stated earlier it's hard to compare apples to apples.
Thanks for the info .....
You may want to go to this site and input your cost of electricity and gas and see what it is actually costing you to produce 100K BTUs of heat/cooling. For the heat pump COP use 2.5. This way you will know for sure whether the cost of a gas furnace is worth while.
Originally Posted by timby
Heat pumps do not produce heat they transfer if from one place to another. Even when it is cold out they can transfer more heat than the energy used to do so. Most higher efficiency heat pumps can transfer 2.5 times the energy (heat) that it uses. A gas furnace burns gas to produce heat, but can not produce more than it consumes, thus the 95% or 80% efficient.
If, after you determine what it cost to produce heat using the above site, change the efficiency of the furnace from 95% to 80% and then you will see how much more it will cost to operate the 80% and be able to figure out how long it will take to cover the cost difference between the two units. If you don't use the gas furnace much, the higher cost of the 95% may not be an investment you can ever recoup, especially if your gas rates are real low.
Do a search on this site for some of the discussions abut SEER, how it is calculated, and how EER (not SEER) is a better method to compare units when in a hot climate like Texas. SEER has become a marketing item - enough said. Two staged outdoor units will provide you with much greater humidity control which will allow for a higher setting on your t-stat which will save you operating costs. While they should not be sold as an energy saver, there is potential for savings over a single stage unit.
I obviously do not know any of the contractors you have been considering, but the price differences may be reflective of the quality of the job they will be doing. Do another search on this site and look for what should be considered when choosing a contractor. There is much to consider and price should be one of the last items on the list.
Good luck. Spend some time reading here and you can learn a lot to help you get a new home comfort system that will give you what you have paid for.
Thanks for the web site. I did what you said and put in my electricity rate of 13.8, which by the way will be increasing soon, and the furnace to 95%. The heat pump will cost nearly twice what my furnace will cost to run. With that being said, I'm only paying a few hundred more for the 95% VS 80% Gas furnace.
One other thing, if the temp outside goes below a certain level doesn't the heat pump require a back up heat source? IF so then I would need either electric or gas as the backup. I don't see how that is figured into the cost for the heat pump to operate. Am I missing something?
I really appreciate the input ....
What is your gas rate.
Must be extremely low for a HP to cost 3 times as much as a gas furnace
When I get home I recheck the NG rate. The one listed seemed to be what I'm paying. I may be wrong. Still I'm paying $65 a month (on the budget plan) for NG. That included heating, range, DHW, and dryer. NG rates in Texas are reasonable compared to the deregulated electric rates (most are paying 14.5 cents). Electricity only seems to go up an arm and a leg every year .
If I had an all electric house I would definitely look into a heat pump.
Still it wouldn't surprise me to be paying a lot less for NG heating. My bill (if I wasn't on the budget plan) in the winter months has never gone above $100. So I'm looking at around $30 to $50 more per month when in the heating season.
All Goodman a/c units are ARI-rated for SEER with the optional ThermoStatic Expansion Valve (TXV) installed in the indoor coil, not with the check flowrater piston supplied with the coil.
Make sure you get the optional TXV so you get the 16 SEER rating under all cooling conditions. The TXV is about Removed Pricing
Best to you.
Please read the rules re' pricing in posts!
Last edited by HeyBob; 04-02-2008 at 05:41 PM.
Reason: Removed Pricing
That system is 46,000 btu cooling, 13 EER, 16 SEER.
Originally Posted by timby
The EER of 13 is outstanding.
Note that it is ARI-rated with "+ TXV".