Heating calculations and heating options

Insulation

This also points to the economic fact that your money is always better spent on insulation than the heating system. It has the best payback. So if you can see a way to reduce your infiltration rates and insulate the walls, you will save yourself that much money right at the start with a smaller design requirement.

 

You might have already said in a previous post, if you will post for me your location ( city and state ) the design temp you want , the BTU load on your house that you feel comfortable with, and the soil / rock type in your area, I will run a loop design for you.

 

Thanks for the offer

Palacegeo,
Thanks but I am comfortable with loop criteria given to me and I do not want to burden you. Both companies offer 10 year warranties on entire system and one offers 55 year warranty on loop field (sounds like an important consideration). I have list of references and will do a bit of due dilligence and make decision. I have decided to go with load calcs assuming exterior wall insulation. It will force me to properly insulate my home.
thanks again, Dave

 

Reply for proper design

Dave, I sent you a message in response to your concerns. Based on what I have read , your contractor in my opinion , MUST be accredited by the International Geothermal Heat Pump Assoc.

 

Long run times in 2nd stage perfectly OK on long winter nights.

I checked Harrisburg, Hagerstown, and York in my design software and winter design temp is 11-12 degrees.

I share Palacegeo's skepticism concerning a minimum Entering water temp of 40 deg F. 30 sounds much more likely. By the way the 80 maximum refers to summer cooling.

Deep ground temperature in your area is likely 55 or so, though I can't find my map of that right now.

To learn more about individual unit's capacity at various entering water temps download Waterfurnace pdf of Envision specifications - tables therein detail capacities for every 10 degrees of loop water temp.

 

IGSHPA accreditation is a good place to start, but should not be the deciding factor.

I have been to IGSPHA training, it is very basic with no hands on training in design or install. In fact they stress that it is not a design course.

The best way to choose a designer / installer is to get references and call them. If they don't have a great track record of happy customers over several years, then you are taking your chances.

I realize that not every one has the option of choosing from well qualified contractors. If you can't find one, then make sure to protect yourself by getting a performance guarantee in writing. Don't pay them in full until you know that the system is performing up to standards.

 

York college

The college in York PA got a lot of press 2years? ago. It is a closed loop design and I think they used 300 foot bores, do not remember the diameter. If you can find out the engineering firm responsible, you will find that they did an actual conductivity test for the project. You may be able to cross over their data.

In regard to a 55 year garrauntee on the loop field, buyer beware, they are promising that the pipe will not fail, not that the field will operate properly.

Eric

 

Consider your current utility-bill..

The best way to decide heating and cooling size determination would be your current heating bill. Using higest heating bill of the month, calculate total energy need (gas or oil volume consummed) for the heating. in terms of calorie or BTU. Then you can easily decide the size of your heat-pump.

Good Luck on Your Geothermal Heat Pump System.

I would go with 5 ton system with supplimental heat or higher. Supplimental heat source does not cost much and will guarantee your heating needs in extreme condition.

SaeHeum Song,
www.noblegeofurnace.com

 

I live in Chapel Hill, NC. For past 15 years I've heated my 3500sf home with an oil furnace. It just died due to a cracked heat exchange. I'm looking at different options and the more I look the more complicated it gets. A friend suggested geothermal heat pump. I spent the weekend trying to get up to speed on all there is to know about geothermal and conventional heat pumps. I thought I was going to be able to replace oil furnace with either a conventional heat pump or geothermal one, but after a heat loss calculation done by a HVAC contractor I learned conventional heat pump would require an auxillary heat source as my heat lost calculation topped out at 209,000 btus. My home is a 3500sf ranch on a slab built in 1954 with lots of floor to ceiling glass. Currently I'm cooling with a 5 ton Trane AC. Contractor says I'm going to need to backup heat pump with either oil or propane gas (natural gas isn't available). First question, given my heat loss calculations, will a geothermal system give me adequate heat or will I need an auxillary heating system as well? Any other suggestions would be gratly appreciated.

 

I'm sure the pros here can give you suggestions. I'm a homeowner and would suggest you get lots of quotes and ask everyone quoting to run a load calculation. Sometimes mistakes can be made. Compare the results.

What have your heating bills been running? :shock:

 

How were the calculations preformed? The reason I am asking is mine was done using the past history of the homes gas bills.

 

209k btuh is an ASTOUNDING heat loss for a 3500 SF home in NC, glass and 1954 construction notwithstanding. That's easily 2-4 times what I'd expect

1st step is to confirm that figure via Manual J load calculation.

Next step is to attack the sources of that load. Perform whatever low-hanging fruit energy improvements are needed to bring that load down, then start in on specifying a replacement HVAC system.

NC climate is at or near the happy medium for HVAC systems such that heating and cooling loads should be relatively close to each other. That simplifies system design.

As a point of reference I have 3400 SF of conditioned space in North Florida (Jax area) easily met with 30kbtuh of HVAC at any outside temperature from 25-95

 

I would be skeptical of anyone espousing the need for supplemental heat tat did not address the "low hanging fruit" Engineer mentioned. It is allways cheaper to better your envelope as part of your mechanical budget, than oversize or supplement anything if budget monies are available.

 

As was mentioned, Your heat load should be relatively close to your cooling load. I'm near lansing MI and a 209mbh load would be high for 3400sf here. Your bidder is either incompetant or mistaken, but oblivious to a glaring disparity (which brings us back to incompetant).
The only thing I could see bringing the load that high is about 8 masonry fireplaces with no doors or dampers.
Get other opinions.
Re. auxiliary heat, we use it around here to avoid grossly oversizing a system to cover the uncommonly cold days. It also doesn't hurt if the primary system locks out. Embrace it don't avoid it.
Good Luck,
Joe

 

Not sure I agree with "embracing" aux heat, but I'd definitely hold its hand and bring it to the party anywhere much north of Interstate 10

 

Have third party professional run the numbers. You can also run the numbers yourself using a program like HVAC-Calc ($50) which is very easy to use (I have not had my numbers verified by a professional yet). You can run different scenarios to see which upgrades with cut your heat loss numbers down. Once you get good numbers, you may not need upgrades.

As I have learned on this forum, it will get expensive in both system cost and installation to depend 100% on the GHP. A stepped aux back-up is available with most systems for the few days a year with the heaviest demand.