Help Decipher Energy Audit Report
I got an energy audit a couple of years ago and completet most of the main recommendations in the report. I am finally ready to replace our HVAC system and have shown this report to 3 different contractos and each one seems to give me a different answer in regards to the size/load of a new system.
Currently there are 2 systems -- gas furnace and A/C (a 2 ton and a 3 ton). The unit is about 10 years old and is rates at 80% efficiency with the A/C units coming in at 10 seer. The house is 3000 Sqft, and located in SF Bay Area -- so pretty mild climate.
Our duct system is a jumble of mess, so it will be completely replaced during this process (one of the main recommendations of the report)
My question is as follows: Given the attached report what size system is appropriate for our house -- both A/C and Furnace? It seems the contractors I am talking to are pushing a bigger system that the report indicates -- but then again the problem might be my amature eyes translating the report.
Can you serve the house with one system?
That is what I am being told -- that a single 5 Ton (York YP9C and a 16 Seer A/C) can easily handle the entire house. However -- given the numbers from the report -- that seems like a bit of overkill.
any 5 ton unit will have at least a 100,000 btu furnace ,5 tons in for 3000 ft in frisco seem kinda big to me .
Originally Posted by ootyboy
So what is the suggested size given the audit/load report?
I don't see where the report mentions what the heat load calc was. I only see the breakdown for heating, not cooling.
An answer without a question is meaningless.
Information without understanding is useless.
You can lead a horse to water............
Yup, they talk about manual J, but no numbers are given.
Originally Posted by tipsrfine
Make your expertise uniquely valuable.
Make your influence uniquely far-reaching.
If they are choosing comparable unit sizes. The bids should be close to apples/apples make your choice and ensure they provide an updated load calc.
Your current heating system is big for your home.No info on cooling provided.
If you think our goverment is screwed up. You haven't lived in another country.
Looking at yoru electric bill, it doesn't look like you hardly use any AC. Get a load calc done, but just based on useage, I'd guess a 3 ton might be big enough for the whole house. Based on gas useage, I dobut you need more than a 60k BTU unit... if even that big.
Honestly, if you current system is still working, I'm nto seeing much savings replacing it.
Now... I'd look at some other energy savings things like lighting, or whatever else your using electricity for. you're over 1000kw-hr even in mild months. Wow! I have a 3200sqwft house with my wife and 1 kid and out Oct. bill (when mininal heating or cooling was used) was around 500kwhrs. You must have a ton of incadescent bulbs you leave on all the time, big TV's, electric water heater, do a ton of clothes or cooling an plug-in electric car maybe? That's some big time base load useage.
SF CA summer design is 85-DB; it was the RH # 75% RH mid-day. My ARI text book shows 71 DB 62 WB; I didn't think that could be right so I got DB WB numbers off the web, so numbers may not be totally correct; that gave the RH% not the wet bulb...
Originally Posted by ootyboy
Therefore it appears you have a high humidity situation with mild outdoor temperatures.
The last thing you want with those conditions is an oversized A/C or heat pump! Someone should have performed a room by room manual J heatload Calc. Five-Tons has to be way too big!
Last edited by udarrell; 12-16-2011 at 12:28 PM.
Reason: Five-Tons has to be way too big! RH # 75% RH mid-day.
Thanks for feedback everyone. It is very helpful.
In regards to the electric bill it has been crazy high. We have a ton of 4" recessed lights in the house with 40W halogen bulbs. Last month I spent a small fortune and replaced them all -- about 40 with LED bulbs that are only 6 Watts. I have yet to see a current bill to see if has had any effect. We also have a Koi pond with a pump that is about 300W that runs 24/7, but aside from that there is nothing out of the ordinary.
In terms of location I am actually more in-land from SF - near a city called Walnut Creek. It does get quite a bit warmer here than in SF. However, we probably use the A/C no more than 3 to 4 weeks a year. The rest of the time the weather is quite pleasant.
As for the reason for the replacement is really a question of comfort. The current heaters just runs and runs and the house is still freezing. I know part of that is the duct work and better placement of the registers/returns(which is part of this project), but I think the heating system is working way too hard and not really doing anything. I was told by all the contractors that the register and return placement will have to be changed to make it better - and they are telling me that the first heater is undersized and the second way over sized.
We do have new insulation in the attic, floors and walls and new energy efficient windows. For a 60 year old house, it is sealed pretty well.
The second unit is way over sized for the area. For a 2 ton unit it has like 4 registers and when it runs it blows very very hard and is noisy. During the summer when we do run the A/C, we've noticed that both units run pretty much all day to just get the house down to 80!!
One of the contractors told me that he will run a a load calculation, but they are all adamant that given our house (ceiling height, windows, flooring) etc. a 5 ton unit is the minimum. All three companies I am working with are local, so they know the area very well -- but I am really afraid that they are all playing it very safe by over sizing the unit...
Originally Posted by ootyboy
Unfortunately, they are all wrong. If your design temp is 85F, then the system should be running constantly when it's a sunny 85F afternoon or warmer. A 5 ton will still be cycling on and off. You don't design for 100F just because once every few years for a couple hours it might get that hot.
That's like buying a minivan to commute to work every day because of the off chance that your wife's van is being repaired so you need a spare. That's what rentals are for. Or buyign a pick-up because once or twice a year you go to Lowes and buy a bunch of lumber. That's why you have that stuff delivered. You get HVAC systems... and vehciles... for what their primary design or what you need them for is 90-95% of the time... not for the 5%. I'm not saying yu only buy practical cars or equipment. You can pruchase featurs based on comfort or preference. If you really love how that minivan drives and rides, than commute in that. Or pick a motocycle, corvette or BMW.
I have a 3200sqft, 2 story, 86y/o old home, I'm in SE Iowa with design temps around 93F, with high ceilings and I don't even need 5 tons. About 4 tons total. And I can cinfirm that based on run time this summer in design conditions. Although the contractor that the previous owners used must have been trained like that one... they installed 7 tons total capacity.