Which HVAC System

Terry_Adks

I am a non-pro with a question about how to determine the most cost & energy efficient HVAC system for a new single-family home.  Specifically, does it make sense to go with a high-end energy efficient system (hydronic & A/C) such as geothermal if the home is built reasonably tight (rigid foam board w/taped seams, extensive use of caulk & spray foam at all possible paths to the exterior, etc.)?  Coupled with mechanical ventilation, I would think a less efficient system in a tight house would be very competitive with regards to install/op/maint costs over a 20-25 year period.  Thoughts please.  Thanks.

Steve Whitbeck

system

It doesn't cost that much more for a 95% efficient furnace. If you have natural gas available then I would just go with a forced air system. even if it isn't and the house isn't real huge and well built same answer.

Geothermal has a shorter life span, is noisier and requires yearly maintenance.

I suggest American Standard/Trane equipment.

The Steam Whisperer (Formerly Boilerpro)

Food for Thought

I have a client who built a tight new home, foamed walls, tightly sealed foundation, etc.  and we installed a radiant floor heat system with a conventional boiler (ventilation was provided for the boiler room).   The customer had a traditional 90% furnace installed when the home was built to provide cooling.   I warned the owner about the need for ventilation, but was ignored.  As winter rolled in, he had enormous moisture problems....windows sweating,etc.  As is often the case with newer conventional boilers, the stack damper failed within the first couple of heating seasons.  Since he had the hot air furnace he turned it on overnight until I could swing by the next day to fix the boiler.   The next morning the whole family woke up with sore throats.... the house was bone dry.    The forced air heating system caused massive amounts of air infiltration  that was not happening when the hot water heat system was in use. 

You could probably guess which system is likely to cost more to heat the home. 

Nuff said.

Jeff Hammond

Re: Which HVAC System

I'm not sure where Tinker gets his/her information, but there are hundreds of thousands of geothermal heat pumps installed, many of which are 20+ years old.  Especially for new construction, where the tightness of the home allows for a smaller system, geothermal is a great fit.  I'm also not sure were the noise issues or yearly maintenance concerns come from.  Most new systems are about the same or in some cases quieter than a refrigerator.  There is no noisy outdoor unit, and if installed properly provide years of trouble free service.  Forced air systems need periodic filter changes like any forced air system.  Geothermal heat pumps used for hydronic heating or radiant floor systems don't need any maintenance.  A yearly check-up, however is recommended for any HVAC system just to make sure that everything is working properly. 



Energy Star (http://www.energystar.gov/index.cfm?fuseaction=find_a_product.showProductGroup&pgw_code=HP) has good information on geothermal systems.  Keep in mind that there is also a 30% tax credit.  Another good website is the GeoExchange website (http://www.geoexchange.org/).  Manufacturers websites also have good information on the technology. 

Terry_Adks

Still Not Sure

Thanks for the responses.  The ventilation post is of particular interest. 



I guess what I'm looking at is total cost for what I call the source (heat pump, boiler, etc.). Assuming the delivery system of ductwork and/or radiant tubing is the same regardless of source, I'm trying to make sure I am comparing like to like. With geo it's not just the GSHP cost but it is also the material/installation costs of the field loops (not insignificant).  Conventional heating systems do not have the field loop component and would be cheaper to purchase and install.  So does the higher (?) efficiency of geo offset the additional field loop costs enough to make it a cost effective choice when compared to conventional heat sources?  Hope that makes sense...

TonyS

Geothermal

I have a 2000 ft. home that has r19 walls and radiant heat with a 36000 btu design day. I replaced the oil boiler  2 years ago with a geothermal water to water pump and dump system. I sit aside of a stream and have unlimited water 15 feet down. Incoming water is always 57 degrees. I take 10 degrees and dump it in the stream. My electric bill increases 75 bucks in the winter. Nothing else even comes close! But I have a perfect set of circumstances for this system. If you have to install a field or wells it becomes very costly compared to a pump and dump and they are not nearly as efficient although water to water geo's are now 30% credit uncapped. On the other hand I had to purchase a inducer motor for a peerless pinnacle boiler the other day. The price was just ridiculous, and the unit was just 5 years old. If the owners would have installed a good cast iron boiler with a thermocouple they would still be ahead of the game. With a well insulated house like yours, the actual dollar difference in fuel between a high tech modcon and a good cast iron boiler will not be that much anything you save will be gone when it comes time for repairs. If your house sits in an ideal place for solar you may want to think about that., Solar is the only fuel that doesn't change in price. Navien is introducing a new combi heater based on its line of tankless water heaters. http://www.navienamerica.com/product/combi_01.aspx?skin=combi_01  . I am waiting to test this unit out, The cost is low,the efficiency high and reasonable to maintain with good warranty. Its just not available yet (mid march).

Steve Whitbeck

HVAC

Jeff - where I get my reasoning for noise and need of maintenance is 34 years of experiance working on Goethermal here in Michigan.

Normal life span of a geothermal system that is used for A/C and domestic hot water is about 15 years. Yes some do live longer but this is not the average.

And I havn't seen a heat pump that was even close to being as quiet as a high end furnace.

I ALLWAYS tell customers to have their geo. system serviced yearly.

GREG LAUER

easy question

Daikin, simply the best.

plenty of options to choose from and more eff than geo.

Gordy

ROI

One must think to the future of fuel costs when calculating ROI. What electricity,NG,LP, and oil cost now is not going to be as cheap in the future. You will have dips, and peaks but the over all chart will be a steady climb.



Another thing which Boiler Pro points out in his post is the characteristics of a  F/A  system verses a radiant in reference to the dynamics of infiltration on a dwelling. Infiltration can raise heating loads considerably while decreasing comfort.



Speaking of comfort that is another critical choice in the decision making process of your "comfort system". The best one is the one you do not even realise is there doing its work.





So its not always about what it is going to cost you up front. The choices can be daunting but keep in mind the cost of what ever fuel you use will not always be as cheap as it is today, along with the comfort system you decide to install.





My take is that a less efficient system in a tight well insulated home is just that. A less efficient system.



Gordy

Terry_Adks

Re: ROI











Thanks for

the responses.  I think Gordy's response goes to the heart of what I'm

trying to ask. I asked this question because I have a geo system and a friend

is getting ready to have a home built. I chose geo because of the supposed

benefits of higher efficiency and lower energy use.  But just the cost of field loop excavation

and backfill for my system ran to a little over $14K.  That’s a lot of money to make up even when

compared to rising energy costs and a less expensive and less efficient system.

And I am not sure I made the right choice. In all fairness, some of my issues

have more to do with a poorly constructed building envelope than with the geo

system  (structurally sound but not very

tight) – which actually goes to my belief that residential construction needs

to be approached from a system perspective rather than as a series of

individual tasks. Thanks again for taking the time to respond.