Pennsylvania Higher than expected electric use

• Location: Bethlehem Pa 18015
• Heat Calculations: Proposals received from two different contractors called for 16, 17, and 20 tons. 20 tons includes heating garage and sun room, where 16, and 17 did not.
• Heat Pumps: System has 4 Water Furnace Envision™ Series NSW NSW060s for about 20 tons of capacity. All supply hot/cold water to a storage tank that is used to circulate water to air handlers and radiant heat. Floors are oak with the coils installed under the sub floor. 15 thermostats control 9 air-only zones and 4 air & radiant zones and 2 radiant-only zones. We have 4 air handlers, one that is used only for the garage. In addition, the three air handlers for the house have steam humidifiers. Each of the 4 HPs has a desuperheater that heats water in a storage tank.
• Loops: 4 ground loops. One (#1) is vertical (4 bores) and the other three (2-4) are horizontal. Vertical was a difficult to drill, so they switched to horiz. All use Twister pipe. Each HP has its own geo loop.
• Electric: Electricity is costing us $0.127 per kWh (total $ on bill / total kWh used) For the period 12/15/14 through 01/15/15, use was 12,395 kWh ($1,576.41). We did just switch to a new energy supplier that should lower the generation charge significantly.
• Air: N/A

• HP -- EWT / LWT
  1 -- 48 / 45.5
  2 -- 52 / 49
  3 -- 47 / 41.5
  4 -- 49 / 45.5

• Geo load: 100%. There is no backup except for resistance heat in 3 air handlers (not in garage)
• Installers: They don't understand why it's so costly to run
• Costs: We don't have much in the way of previous or expected. We did major renovations to home (added area) and previous owners didn't use the house much.

The system is using a Tekmar 406 control. This control is capable of controlling only two HPs or one 2-stage heat pump. The other two heat pumps kick on using delay timers & relays. With the 406 choosing when to turn on the 2nd HP and the 10-minute delays, the secondary HPs were barely running. After changing the delay to approximately 2 or 3 minutes, the secondary HPs are in use more. (See attached images)

I have a data acquisition system that measures Amperage draw of each of the HPs and temperatures (RTDs on exterior of pipes at the Flow Center). Note that the values of Amperage are off by a factor of about 145x.

The contractor who sold and installed this system led me to believe that the electricity consumption would be equivalent to that of several 100 W light blubs, so I was very shocked to see a $1500 electric bill.

1. Are all of these frequent startup / shutdowns across 4 HPs significant?
2. Is it possible to use a Multi-Staging control like the Tekmar 284 (http://tekmarcontrols.com/products/multi-staging/284.html) to control the HPs better?
3. What is a good duty cycle for these HPs?
4. Is it okay to send 110 to 120F water under my wood floor (it’s installed under the ¾” sub-floor)
5. Is there any sort of bench marking method for how much electricity I can expect to use?

 

I'll let the experts comment on your system and setup, but in the meantime, you can see how other systems perform at the following sites:

http://groundenergysupport.com/wp/live-sites/
http://www.buffalogeothermalheating.com/sample_diagram.html

 

What are your load temperatures, meaning feeding the air handlers and zones? leaving the heatpump?
What model number is on your circulation pumps for the loop field? Is the a common loop field for all heat pumps? I assume that each HP has a separate loop field. A horizontal twister pipe. That is a first I hear.

Pics of your system and your manifolds for the air handlers, radiant floors would help to get started.

 

Doc gives good advice and questions. We do the same job, but do not always agree on how to get there.

Heat pumps are sized for cooling load. I do not see heat loss in your typing.

I know 406 controls.

I think the issue is in how the controls and zoning operates.

Mark

 

EWTs look very good for latitude and time of year. LWTs look a bit high, as though pumps are oversized. 110-120*F sound high for radiant floor water, particularly beneath wood.

400 kWh / day seems quite excessive even for the tonnage installed, but we don't know what of that figure represents consumption by HVAC. In very round numbers a ton-hr of geo HVAC should burn somewhere around 1 kWh, a bit less if the system is well designed and installed.

 

Need alot more actual detail as in heat loss, pump strategy and yes why do we need 110-120F water?

 

Thank you all for the questions. I hope I have answered most of your questions below.

I picked up a thermometer that someone within the site recommended and have learned that the temperatures that I had been reporting were grossly inaccurate. (RTDs on tubes / fittings)

I just measured the following:

HP1 (Vertical Loop)
EWT: 41.9F
LWT: 37.2F
To Tank: 111.9F
From Tank: 107.2F

HP2 (Horiz Loop)
EWT: 39.3F
LWT: 34.3F
To Tank: n/a
From Tank: n/a

HP3 (Horiz Lop)
EWT: 34.3F
LWT: 29.3F
To Tank: 114.8F
From Tank: 109.9F

HP4 (Horiz Loop)
EWT: 37.2F
LWT: 32.3F
To Tank: 121.4F
From Tank: 115.5F

Outdoor: 32F
Tank Target was 120


All air handlers and radiant zones are fed from the storage tank. There is no mixing to modulate water temperature. See above for some output temps on the heat pumps. All heat pumps have desuperheaters.

Loop circulation model is FC2-GL; pumps are GeoLink Type UP26-99U. Yes, each Heat pump has its own separate loop. The vertical twisters were grouted; horizontals were not.

I don't have access to any of the heat loss calculations for the house. The only thing that I do have is oil consumption from last year when I was keeping the house at about 55F and it was bitter cold. In 8 weeks, I went through about 800 gallons of oil.

I was told by contractor that he would use mixing to keep floor water temp lower but now he insists that it's not necessary, that 120F water under sub-floor is okay.

 

Just started a new business in Washington, PA, but a little far for us to help i think!

Do you have a one-line drawing or can you sketch one how the heat pumps are connected to your buffer tank and than to that manifold and how rest of system piped? etc...

 

Each heat pump has a circulator pump that connects to a manifold to the storage tank. Return lines are from a manifold, too.

Load side of storage tank is a large manifold with 9 circulators off of it. Returns are handled the same way.

Let me know if you need more detail. Thanks!

Here is a picture of the zone ciruculators:


Heat pump manifold:

 

This is a tough one on operations. With your load setup, those pumps can and will interfere with one another. So your flows will vary depending on zone calls.

I would have preferred to see hydraulic separation either through closely spaced T's or a hydraulic separator. This would have allowed for different load temperatures as well.

BUT, your real question is energy usage. Turn everything down to 100F. Your fan coils may want more. But just try 100F for now.

You can also set your timer relays for longer delays between staging. Start with 20min. Then set the 406 to around 60min. Assuming I understand how you've currently staged your equipment. So you have 1 pump, 2 pumps at +20min, 3 at 60min, 4 at 80min.

 

Does the house require a 120F target temperature to keep the house warm. Moving that target temp to 100-110F will raise the COP for the Geo by .5 - 1.0. This would most likely save some energy, but with all those circulator pumps it hard (for me) to say for sure.

Can you pull off the model number off the other circulators? (the geo manifold and zone manifold)
" electricity consumption would be equivalent to that of several 100 W light blubs" - Each circulator pump is 1-2, 100 W light bulbs...
So lets see:

(8-UP26-99U)(2) = 16 100W bulbs
(9?) - zone circulator pumps = ? 100W bulbs
(4?) - Geo manifold = ? 100W bulbs
and then you still have the geo systems to add onto that.
Guessing his idea of 'several' was a higher number then yours.​

3 steam humidifiers - These things can be expensive to run.

I love my steam humidifier, but I need to keep it in check based on what humidity level I need in the house compare to the outdoor temp. (I will have that automated shortly with a new control I'm building) ​

Can you tell us more about your loops - size of pipe, length of pipe. (really looking for total length of pipe per loop)

How large is your buffer/storage tank?

 

The 406 allows for only a 20 minute delay between heat pumps. I set it to 20 and made set the timers to 27 minutes. So now it will go:
0:00 HP1
0:20 HP2
0:27 HP3
0:47 HP4

I could not find a setting on the 406 to limit the Tank temperature--it's calculated based on outdoor temperature. I did find a setting called HP Return Max that prevents the HPs from operating in heating mode if the heat pump return temperature exceeds this setting. I changed it from 120 to 115. I'm a little reluctant to change it to 100F.

Any advice on how to limit the max Tank temperature calculated by the 406?

I also change the HP SOURCE from GEO to AIR so that both HPs don't need to shut off at the same time. I didn't see any other impacts of this setting.

The Storage tank is 80 Gal.

The system is only running about 2-1/2 months, so I'm not aware if changing the tank to less than 120F will have an impact. The house is quite comfortable as is.

HP circulators are Geolink by Grundfos model UP 26 99 F (4 each)
Zone circulators are Grundfos UPS 29 99 FC (7 each) and Wilo Typ Star S 21 FX Nr 4090765/12w09

I'm pretty sure that each of the twister pipes is 200 ft long and each loop has 4 of them. The verticals didn't make it 200' down, so the excess is snaked around at about 10' deep. The three horizontal loops have at least 320' of pipe between HPs and start of loops. These are in the back yard and the vertical are in front, much closer to Mechanical Room.

 

You want to change the "tank design temperature". This is the setting the tank is trying to reach at your "design temperature". Or the hottest it will be on the coldest expected day.

Your right about the 406 having a max of 20min delay. I didn't realize that. I guess you could put a timer relay on the 2nd unit call.

 

I'm sure the pros will chime in here more.. but I'm sorry to say it seems your designer/installer didn't understand the water flow requirements on the load side.

4 - 6 ton units ideally you would want to push 18*4= 72GPM... They are trying to dump this load into one storage tank. To handle that flow you would need 3" copper.
2.5" copper would get you 61 GPM which might be close enough (but I would guess if you are lucky you might have 2" copper - 40 GPM)

You should ask them for the design details...

For the loop field I would still want more details. - So far I know each loop is 4x200' of pipe; Are these connected in serials or did they do a header? What is the diameter? 3/4", 1"??? For the horizontal loops, what sizes of pipe did they use in that 320' run? 1.25", 1.5"??

 

I changed the Tank Design Temperature from 112 to 100. The Tank Target is now fluctuating between 106 and 110.

Do you think I should lower the Tank Design to 90F to get the target to land closer to 100F or is this adequate?

Since increasing the delay times, only 3 of the HPs are running. (Note that vertical axis "0.20" = approximately 29 AMPS) The challenge with adding an additional delay to the 406 is that it rotates which starts first. I'm sure it can be done, though.


The heat pump circulators are using 1-1/4" but this increases as it approaches the storage tank (after the final circulator connection).


Zone side of the storage tank appears to be 1-1/2" copper and each loop Ts off to 1".


So are you saying that the four 6-ton units are too much for one 80 gal tank? That the system will continue to short cycle b/c the thermal storage capacity is too small and the ability to add and remove heat to it is hampered by the small tubing? What is the fix? Add additional storage tank(s) in series and create a larger diameter manifold? The storage tank has 2" connections. (GeoStor 80GST)

I'll work on getting more details on the loop fields and system design.

Thank you!

 

You usually want something like 10gal per ton.

I'd also 2x all the temp readings. As in, make sure the sensors are actually getting the correct reading. A clamp thermometer works well for this.

 

Yes, you need another storage tank.... whether you need another 80 gal tank or if you really need 200 gallons total, I'm not sure. To keep the plumbing to a reasonable size I would think it would be better to have the circuits in parallel. Depending on your loads, you could break the 20 ton system into 2 - 10 ton systems. This would give you the ability of feeding higher temp water to your air handlers vs the floor zones. (but again, this all depends on the demand of your loads)

Looking at the system performance chart:

With your current plumbing, it seems like you can support 40 GPM max. Once that 3rd HP kicks in your overall COP would drop about 7%, (2.3% for each running HP). Once the 4th HP kicks in your COP drops another 8%. (~2% for each running HP). So 15% under where you really should be.
​

With changing your target temp from 112 downto 100... that should have gotten you around a 12% increase in COP as well.

 

Two 120 gallon tanks would be feasible in my mechanical room; adding just one more 120 seems like it would be simpler. Any recommendation for brands / types? Of the 9 zone calculators, only three are for radiant under wood. Two are for radiant under carpet and tile, so it would seem to me that the path forward would be to combine the tanks and then provide mixing to the wood floor zones if necessary. Would the two just get hooked up in series on zone and geo sides with a temperature probe in just one of them? Could they be in series on Geo side and parallel on Zone side?

I reinstalled all RTDs, ensuring good contact with metal fittings and I will also attempt to calibrate them.

 

If you could draw up your existing plumbing, I could take a stab at making a recommendation. I know the Tekmar so we could sort the plumbing to have different supply temps relatively easy. Assuming you're putting in a second tank anyway.

Also, check your temperature differential on the control. Keep it wide say 6-10F. This is the swing on the system. So if your tank design is 100F it will drop to 95F and rise to 105F (if set to 10f). If you have a tighter temperature band, things can sometimes act a bit funny with it heating too much. Something to do with the algorithm I'm not privy to.

 

Temp differential was 4, I changed it to 8.
I will work on a plumbing diagram today, thank you!