Missouri System oversized....or something else?

The fact that your are oversized should not make your system inherently inefficient.

The 4 ton units are quite efficient, and you run longer in the more efficient 1st stage. You have more strain on the compressor in the very long run, and less comfort, and might have a cycling loss of of 5-7%, higher up front costs, but this kind of oversizing with 2 dual stage units does not necessarily explain your lack of efficiency. So you have effectively 4 stages of heat.

From the distance it smells a bit like a zoning issue, especially when you don't feel much air coming out of the register. Why do you zone combined space? 97F supply temp means a delta T on the air size around 30F, which might suggest not enough air flow. What is the model number on each of your 4 circulation pumps? Right now it seems like you are running 2 circulation pumps per heat pump when only 1stage is calling, which seems to be most of the time.

Giving your large windows, your house might be designed for a large heat gain, so it might be cooling dominated, with the capacity designed for cooling.
Some of the zones seem very small for 2.5 tons coming from 1st stage.

Just some thoughts so far. Check your circulation pumps for the model #...

 

Hi Doc,

Pumps are B&D Grundfos 230V - 2699 3/Spd Pump. As far as register air there is no issue with the South unit, only the North unit and only when both zones 1 and 4 are calling at once. That issue is not present now that I've changed the system to call for 2nd stage if both zones are calling. There are a total of 13 registers being utilized when both zones are calling. This is still something I will have our contractor check.

As far as combined space I'm not sure why zones 1 and 2 were not combined as one zone. I think it was due to the large open space and trying to even out temperatures throughout the main floor. My Delta T on the air side with desuper running is about 23 degrees. Without desuper is 29-30.

I can say that with the changes made so far my energy usage has dropped significantly. My whole house kwh usage for Nov 24 - Dec 24 was 4,000 kwh's, about 130 per day. This was with the fireplace running to help with heat a great deal of time as well. My current usage the last 5 days has dropped to an avg of 65 kwh's per day.

Also something new found today. I run the units fan when operating the fireplace to help circulate the heat throughout the house. I did not realize that turning on the fans for even one t-stat opens the dampers for all zones. When doing this I was pulling cooler basement air into the returns.

Lots of small things that are quickly adding up to big savings. Thanks Doc.

Jeremy

 

Such a deal !!

 

Make and model number for a start. Your drawings are on the top of the pile on my desk.

Mark

 

"AMI would you care to elaborate on what issues the zoning could cause, or a link to another discussion here that would be helpful?"

Sure most efficient systems have adequate air flow for each ton of heat pump. If you are running first stage in heat pump you need something like 1100 CFM or so. If a single zone is not enough to carry that then you would need a strategy to dump the remaining CFM which could be wasteful. But it is all speculation without numbers. As Doc mentioned it sounds like your airflow may have been choked.

"A blower door and thermal imagery analysis for $100 is a steal, go for it! Your fellow ratepayers are subsidizing the cost since there is no way to deliver those services for just $100."

Only a deal if it is done well. One of my clients opted for the utility company guy instead of who I recommended. They determined the infiltration rate on his log home was excellent......and it would have been if the home actually was 6000 SF versus the 3000 SF it really was. Sometimes it's not subsidies, sometimes it's utility company hacks who have minimum wage crews that hopefully get the math right.

 

Ultra-zone Model: ND Rectangular Dampers with MA-ND5 Actuator. PDF of zone paperwork attached.

AMI thank you for the info about zoning. Well noted about the blower door test (which I had to move to next week due to work). Our electric company is a Coop and the service to date has been outstanding. I know the gentlemen who is coming out to do the test. He has been with their member services department and is one of two who lead their energy audits. He has been with them for several years so hopefully he's knowledge is better than some of the guys it sounds like you've had issues with.

 

Cool!

 

Looks like I uploaded the same page twice. Here's the 2nd page.

 

What have you got that will show control strategy? Dampers are dampers, they are open or closed.

I am looking for the ability to determine weight of each zone.

Duct sizing would be nice like in your photos what goes where and what size are the trunks?

I want to look at sizing and square footage of area served. I am then interested in the size and number of diffuseres for each zone.

I am going on a four day road trip to work on four geo rescues so there is no hurry.

Mark

 

Thanks Mark. I've got a busy week with work coming up but will work on this when I can. What tools do you recommend for unit readings?

Jeremy

 

Make and model number would be helpful.

Dwyer makes a simple airflow meter that runs around $50.00 when I bought mine. I think the model is either 410 or 412.

A good thermometer.

Mark

 

Just about done with my audit were going through at work and have a little more time on my hands now. I picked up a thermometer for water readings. Waiting on an airflow meter. Here's my current numbers for our units.

North unit - t-stats set at 70 - readings stage 1, 30 minutes of run time, desuper off, pumps set at medium speed right now.
CFM stage 1 - 1123
EWT - 37.7
LWT - 32.1
EAT - 71.7
LAT - 90.7

South unit - t-stats set at 72 - readings stage 1, 30 minutes of run time, desuper off, pumps set at medium speed right now.
CFM stage 1 - 1123
EWT - 37.6
LWT - 31.9
EAT - 72.6
LAT - 95.9

Units are drawing 13.2 amps. This includes the pumps as they are powered by the units. How do these numbers look to you guys? Air temps taken at the same location on both units. Any concerns about the difference in the LAT between the two units? Any other numbers needed to get an idea of performance?

Mark - I'll work on the duct work details next.

Jeremy

 

Doc I have re-read past posts which made me think about a couple of comments you made. The air flow comment got me checking registers. Our master bedroom zone had 3 of the registers closed off. I think this was creating a choke point given how small this zone already is and may have been the zone calling when I was reading the higher air delta on the south unit. I re-checked numbers today and both units look good. Here are the numbers if anyone cares to comment on them?

North Unit - Stage2, all zones running
EWT - 37.9
LWT - 33.2
EAT - 71.9
LAT - 95.1

South Unit - Stage2, all zones running
EWT - 37.8
LWT - 33.1
EAT - 72.3
LAT - 94.8

Your second comment about running two circulation pumps when only 1st stage is calling is correct. In fact, I don't think I would hardly ever need anything but 1st stage. Our last cold snap got temperatures down to -9 degrees here on the coldest night. My run-timers that night from midnight to 8am showed 5 hours 30 minutes total run time with 40 minutes of that run time in stage 2. (I only checked the south unit that carries more of the load). Given this would it be possible to run only 1 pump per unit? I can trick the zoning programming so that it never calls for a stage 2.

 

One gets what one pays for.

Free internet help is just that.

Ask Tamar. I did not do the work, but knew it could be done.

Next time I am north I will go look and let her buy me a beer.

Mark

 

You numbers look good, are they in stage 1 or stage 2? I would leave it like it is, you have the flow you need, unfortunately your loop field(s) seem to be designed for that pumping power.

 

Stage 2 with all zones calling. Grundfos 2699 pumps set to medium. Thanks.

 

Not much room to change there. Your loop field design requires the pumping power.

 

Thanks for the reply Doc. I'm anxiously awaiting our next electric bill. Should have it in the next few days. Until then I'm not going to worry about much else until I get an idea of how our usage is with changes. Our units no longer seem to cycle in 10-12 minute intervals, house is comfortable, and our desuper is bringing the buffer tanks up to our 120 setpoint on the colder days when everyone is away for school and work.

Looking at past bills our usage was averaging around 84 Kwh's per day without the heat or air running for the months of Sept., Oct, and Nov. This should give me a rough idea of what we are now using for heat when the next bill comes.

 

I have found out through our utility rep that I am able to get our meter usage data through their smarthub app. I've logged in to pull the current usage and compared to past usage. I am very pleased with what I am seeing so far and would like to give a big thank you to everyone who has chimed in to help and comment. I am going to summarize a comparison below along with the changes we have made to get us to this point. My usage comparison is based on a three week period with the same avg. temperature. ( I only have about 3 weeks of usage with changes under our belt so far).

Here's our usage comparison with changes. This is whole house electric and includes everything, not just heat.

Our baseline usage without heat or air in the fall was an avg. of 82 kwh/day (2460 Kwh per month)

Previous usage - Dec. 5 - Jan 1
Avg outside temp - 32
High - 62
Low - neg 1
Avg Kwh/day - 133 (4,000 Kwh per month)

Current usage - Jan 15 - Feb 10
Avg outside temp - 32
High - 72
Low - neg 5
Avg Kwh/day - 89 (2670 Kwh per month)

So far I am very happy with the results if the trend continues. We are now only using an avg of 7 extra Kwh per day heating the house compared to what we were using without our HVAC running. Below is a list of changes that have been made.

1. tstat call moved to a higher differential of 3. The temp now drops and rises just a bit more so that our run times are longer. Comfort level does not seem to be affected. This has really helped on the short cycle times we were experiencing.
2. Zones for the north unit set at 1 degree below the south unit. This seems to help slightly with letting the south unit pull more of the load and reduce cycle times.
3. Tricked zoning so that only 1 stage runs most of the time regardless of how many zones are calling. The only time the units now call for 2nd stage is if the tstat temps drops more than 2 degrees below the setpoint.
4. North unit 1st stage CFM increased by 5%. Seems to be enough airflow now when both zones on the north unit are calling. No longer need 2nd stage when both zones call.
5. Ceiling fans turned off during the day in all bedrooms (still on for the vaulted living room). Thanks to Mark for pointing out they should be for decoration only. They were needed in our old house for air movement and just assumed they would be needed here as well.
6. Blower door test showed a decent size leak behind one of our corner timbers in the loft and through the adjacent bedroom dormer. Foam injection stopped the leak and now the one cold bedroom I attributed to the very large wall of windows is now warm.
7. Installed buffer tanks for both units. Purchased Marathon water heaters for our powered units and moved the metal tanks to our buffers. I think we were actually cooling our hot water with the single tank setup. I believe that moving to a two tank setup has substantially helped with our hot water cost.
8. Started doing a load of laundry in the morning to take advantage of the buffer tank heat buildup overnight. Gives us all day for the tank to reheat before starting laundry or showers again in the evening.

If our usage trend continues I will be thrilled with our current setup. I'm also anxious to see how the two tank setup helps with our hot water cost when we move to our cooling cycle. I'm open to suggestions if anyone has additional ideas for improvements but right now I am happy with our geo again. Thank you everyone who has chimed in to help.

Jeremy

 

Edit - One other note of importance. After two consecutive billing cycles of 4000 Kwh usage we have also been more aware of turning lights out before leaving for the day, opening blinds every morning to take advantage of solar gain, etc, etc.....