Air-to-Water Heat Pumps for Low Energy & Net Zero Houses
Air-to-Water Heat Pumps for Low Energy & Net Zero Houses © Copyright 2018, J. Siegenthaler, all rights reserved. The contents of this file shall not be copied or transmitted in any form without written permission of the author. All diagrams shown in this file on conceptual and not intended as fully detailed installation drawings. No warranty is made as the the suitability of any drawings or data for a particular application. presented at: John Siegenthaler, P.E. Appropriate Designs Holland Patent, NY www.hydronicpros.com presented by: February 14, 2018 8:30-10:00
- Most North America heating professionals are familiar with ductless mini-split heat pumps. www.johnstone.com Ductless mini-split heat pump airconditioning-repair-nashville.com geothermal heat pump
- Most are also familiar with geothermal heat pumps air-to-water heat pump ?
- Very few are currently familiar with air-to-water heat pumps.
2014 global market: 1,745,000 air to water heat pumps sold Japanese manufacturers [Daikin, Mitsubishi, Fujitsu, Hitachi, Samsung, LG, Toshiba] German manufacturers [Dimplex, Wolf, Viessmanm, Bosch,Vaillant] Canadian manufacturers [ThermAtlantic, Nordic] 2014 China market : 987,000 units (12% increase over 2013) 2014 European market: 232,000 units (5% increase over 2013) #1 France, #2 Germany, #3 UK Still only about 2% of heat sources sold in Europe Due to low gas and oil prices, AWHP are subsided in Europe based on CO2 reduction targets, rather than energy efficiency.
Many current models use inverter drive variable speed compressors for capacity control.
Some use EVI (enhanced vapor injection) compressors. Global air-to-water heat pump market: According to JARN (Aug 2015) This is not the case in other global markets...
So what is an air-to-water heat pump? evaporator TXV comp. RV condenser fan cool outside air cold outside air air-to-water heat pump (in heating mode) warm fluid hot fluid heat to building OUTSIDE INSIDE circulator liquid refrigerant changes to vapor absorbing heat liquid refrigerant liquid & gaseous refrigerant hot gas cool gas hot gas condenses to liquid releasing heat In heating mode: The heat pump extracts low temperature heat from outside air, and transfers it to a fluid stream (water or water & antifreeze) to be used by a hydronic distribution system. evaporator TXV comp. RV condenser fan warm outside air hot outside air condensate drain heat from building cold fluid cool fluid OUTSIDE INSIDE circulator air-to-water heat pump (in cooling mode) hot gas cool gas hot gaseous refrigerant condenses to liquid releasing heat liquid & gaseous refrigerant liquid refrigerant vaporizes absorbing heat hot gas liquid refrigerant In cooling mode: The heat pump extracts low temperature heat from a fluid stream (chilling it), and dissipates that heat to outside air.
14" x 8" duct this cut would destroy the load-carrying ability of the floor joists 2 x 12 joist 3/4" tube Water is vastly superior to air for conveying heat A given volume of water can absorb almost 3500 times as much heat as the same volume of air, when both undergo the same temperature change Why hydronics vs. forced air?
Split system air-to-water heat pump Indoor unit Heating mode: 1. condenser 2. circulator 3. expansion tank 4. aux element 5. controls Cooling mode: 1. evaporator 2. circulator 3. expansion tank 4. controls Outdoor unit Heating mode: 1. compressor 2. evaporator 3. expansion device Cooling mode: 1. compressor 2. condenser 3. expansion device indoor unit INSIDE OUTSIDE outdoor unit refrigerant lineset
Split system air-to-water heat pump European split system air-to-water heat pump supplying heating and domestic hot water -4 ºF outside, 113 ºF leaving water temperature www.NIBE.eu
- It’s not just about matching BTU delivery to load... Ductless mini-split heat pumps rely on forced air delivery. While generally acceptable for cooling, forced air delivery doesn’t provide optimal comfort for heating.
- There will be some temperature stratification from floor to ceiling.
- Mini-splits blow cool air into spaces while defrosting outdoor unit.
- Cold floors are a common complaint with forced air heating.
- High wall cassettes do little to counteract natural downdraft from large window surfaces.
- Forced air heating may aggravate allergies or other respiratory symptoms.
- There will be some sound from forced air terminal units. Properly designed radiant floor, wall, and ceiling panels can operate with virtually no detectible sound. www.amazon.com It’s about providing COMFORT
historicshed.com Training programs for “net zero” houses often promote mini-split heat pumps as the only necessary heating & cooling system. They often discourage the “complication” and cost of hydronic systems. Why is the “net zero” housing market defaulting to mini-split heat pumps rather than hydronics? source: Revision Energy
Based on this - who can blame them ??
historicshed.com Common suggestion for net zero houses... Install a ductless mini-split air-to-air heat pump, with 1 or 2 indoor wall cassettes, and leave the interior doors open for heat distribution.
from a green building website blog... “Leave bedroom doors open during the day If you want to heat your house with a ductless minisplit located in a living room or hallway, you’ll need to leave your bedroom doors open during the day. When the bedroom doors are closed at night, bedroom temperatures may drop 5 F° between bedtime and morning.” “If family members don’t want to abide by this approach, or don’t want to accept occasional low bedroom temperatures during the winter, then supplemental electric resistance heaters should be installed in the bedrooms.” The COPs of cold climate ductless minisplit heat pumps at sub-0ºF ambient conditions is seldom discussed.
source: Revision Energy Maintaining heating capacity at sub-0ºF conditions doesn’t imply that COP is being maintained.
What happens to the COP of ductless mini splits at low ambient air temperatures? Site 1 : COP = 1.1 at 0 ºF Site 4 : COP = 1.8 at 0 ºF
Low ambient air-to-water heat pump yields good performance at low outdoor temperatures: At ambient = 0 ºF, leaving fluid = 120 ºF, COP =2.04
Low ambient air-to-water heat pump performance COP = 2.04 at 0 ºF ambient and 120 ºF leaving water temperature. Heat pump power: 5817 watts Distribution circulator power: 25 watts Heat pump circulator: power: 200 watts Total power to system: 6042 watts Heat pump heat output: 40,500 Btu/hr Higher than the measured COP of several ductless mini split heat pumps @ 0 ºF ambient.
COPHP+circulator = 40,500 Btu hr 6.042kw ( ) 3413 Btu hr kw 1.96
- historicshed.com Ductless mini-split heat pumps provide heating & cooling
- Room-by-room zoning An air-to-water heat pump has the potential to provide:
- Zoned cooling (air & radiant delivery)
- Domestic water heating
- Pool heating in summer
- Higher distribution efficiency
- Fewer (if any) interior refrigerant piping connections
- Radiant & convective heat delivery
1. Growing interest in Net Zero houses: The typical net zero house has a very low loss thermal envelop, and a sizable solar photovoltaic array on the roof.
Net metering laws - where they exist - allow owners of photovoltaic systems to sell surplus electrical power back to the utility at full retail rate. Thus, surplus kilowatt hours produced on a sunny summer day could conceivably be “parked” on the electrical grid, and reclaimed to run a heat pump on a cold winter night with no technical or economic penalty.
Space heat + DHW loads are so small it doesn't pay to put a gas meter on these houses. AWHP could provide heating, cooling, & DHW Source: Zerohomes.org Several trends suggest that a growing market will emerge for air-to-water heat pumps. Here are some key indicators:
- Net Zero house in Seattle SPECS
- 2,426 Square feet
- 4 Bedrooms
- 2.5 Baths
- Radiant heat
- Air-to-water heat pump
- SIP construction
- 9.5 KW PV system Source: www.tclegendhomes.com
- Superior comfort: Radiant panel heating is better match to human physiological comfort needs. It’s not just about pushing Btus into a space to match heat loss. What are the advantages of using hydronic heating in these houses?
- Easily adapted to renewable heat sources) (solar thermal, hydronic heat pump, biomass) source:Wagner Zaun Architecture
- Simple room-by-room (“wireless”) zoning is possible with many heat emitter options. Don’t have to leave all doors open for internal heat balancing. A limitation of single point heat/cool delivery such as wall cassette.
- Very high distribution efficiency (A single ECM circulator operating on 10 to 40 watts supplies all heating distribution)
- Non-invasive installation of small tubing (3/8” & 1/2” PEX, PERT, or PEX-AL-PEX) (Installing this tubing is like pulling electrical cable)
- In many cases a single heat source can supply heating and DHW (fewer burners, less vents, less fuel piping)
- Water-based thermal storage is easily adapted to “time-of-use” Electric rate structures.
What is distribution DISTRIBUTION EFFICIENCY? Efficiency = desired OUTPUT quantity necessary INPUT quantity Distribution efficiency for a space heating system.
Consider a system that delivers 120,000 Btu/hr at design load conditions using four circulators operating at 85 watts each. The distribution efficiency of that system is: distribution efficiency= 120,000 Btu/hr 340 watts = 353 Btu/hr watt distribution efficiency= rate of heat delivery rate of energy use by distribution equipment
The electrical input power for a circulator can be estimated: A typical wet-rotor circulator with PSC motor has a maximum wireto-water efficiency of about 25 percent. (ECM circulators will have significantly higher wire-to-water efficiencies) we = 0.4344 nw/w = 0.4344 × 5× 3.83 0.25 = 33.2watts Consider a 200 ft long circuit of 3/4” copper tubing operating at 5 gpm with 180 ºF supply and 160 ºF return water temperature. It would have a pressure loss of 3.83 psi The required electrical input power to operate this circuit is: we = 0.4344 nw/w We = electrical input power (watts) f = flow rate (gpm) ∆P = pressure drop of circuit (psi) nw/w = wire-to-water efficiency of circulator
Compare this to a 4-ton rated geothermal water-to-air heat pump delivering 48,000 Btu/ hr using a blower operating on 1080 watts. The distribution efficiency of this delivery system is: nd = Q we = 50,000Btu / hr 33.2watt =1506 Btu / hr watt nd = Q we = 48,000Btu / hr 1080watt = 44.4 Btu / hr watt These numbers mean that the hydronic system delivers heat to the building using only 2.9 percent (e.g. 44.4/1506) of the electrical power required by the forced air delivery system. With good design it’s possible to achieve distribution efficiencies > 3000 Btu/hr/watt This will become increasingly important in low energy and net zero buildings...
A flow of 5 gpm in a circuit with a 20 ºF temperature drop is moving about 50,000 Btu/hr. The electrical input to a standard PSC circulator operating at 25% wire-to-water efficiency is 33.2 watts. The distribution efficiency of such a circuit is:
- Consider a design heating load of 30,000 Btu/hr
- Assuming a common ∆T of 20 ºF across the heat emitters f = Q 500(∆ T ) = 30,000 500(20) = 3gpm
- Each panel rad is 24” x 72” x 4” operating w/ average water temperature of 110 ºF, (120 ºF supply & 100 ºF return) yielding output of 3,850 Btu/hr each, total system heat output of 30,800 Btu/hr
- Flow rate per panel radiator is 3/8 = 0.38 gpm
- Head loss of each panel radiator (balance valve partially closed) at this flow rate is 3.38 ft.
- Assume each homerun circuit is 120 ft of 1/2” PEX at 0.38 gpm, head loss = 0.8 ft.
- Add 10% safety factor to head loss for a total of 4.6 ft.
- Circulator requirement is 3.0 gpm at 4.6 ft.
- Even with an ECM circulator that’s 30% w/w efficient, this requires an input of about 8.6 watts we = 0.4344 × f ×∆ P ncirculator = 0.4344 × 3.0 × 4.6 0.43 ( ) 0.3 = 8.6watt distribution efficiency = 30,800 Btu hr 8.6watt = 3581 Btu / hr watt
- Assume a homerun distribution system to 8 identical panel radiators heat source pressure regulated variable speed circulator buffer tank TRV manifold station 8, 24" x 72" x 4" panel radiators 120 ft x 1/2" pex homerun circuits 3-40 watts
Why is the NA hydronics industry leaving its “best cards” on the table? distribution efficiency = 30,800 Btu hr 8.6watt = 3581 Btu / hr watt pressure regulated variable speed circulator TRV manifold station 8, 24" x 72" x 4" panel radiators 120 ft x 1/2" pex homerun circuits 94 3581 = 2.6% In this comparison the hydronic system uses only 2.6% of the electrical energy required by the forced air system for equal heat transport (source to load). distribution efficiency= 80,000 Btu/hr 850 watts = 94 Btu/hr watt
2. The 30% federal tax credits on geothermal heat pump systems ended December 31 2016: That removed a significant purchasing incentive, and forces geothermal heat pump systems to compete against other types of heat pumps in an unsubsidized market.
Several trends suggest that a growing market will emerge for air-to-water heat pumps. There’s a possibility this tax credit could be reinstated. Do you want to build your business model on the assumption that subsidies will always be there? “The GHP industry experienced a 50% loss of residential sales during the year (2017), with hundreds of layoffs and thousands more jobs in jeopardy.” https://www.geoexchange.org/wp-content/uploads/GEO-Industry-News-January-20 18.pdf NYSERDA does have $1500 / ton (cooling capacity) GSHP rebate program at present.
https://www.nyserda.ny.gov/All-Programs/Programs/ Ground-Source-Heat-Pump-Rebate THIS CHANGED 2/9/18
3. Air-to-water heat pumps are significantly less expensive to install compared to geothermal heat pumps: Several trends suggest that a growing market will emerge for air-to-water heat pumps. air-to-water heat pump typical installed cost = $(30% to 50%)X geothermal heat pump typical installed cost = $X This is especially true if vertical boreholes are required for the earth loop. In my area, these holes cost about $3,000+ per ton for drilling, pipe insertion, and grouting.
Additional cost is incurred for connecting multiple vertical piping loops, and routing piping back to the location of the heat pump. Replacement of any affected pavements or landscaping also needs to be factored into the cost of installing a geothermal heat pump system.
4. Diminishing returns: As home heating loads decrease due to better thermal envelopes, the difference in annual heating cost between heat pumps operating at seasonal average COPs that vary by perhaps 1.0 or less, decreases. air-to-water heat pump typical installed cost = $(30% to 50%)X geothermal heat pump typical installed cost = $X Several trends suggest that a growing market will emerge for air-to-water heat pumps. Here are some key indicators: The incrementally lower operating cost of the higher performance heat pump may not amortize the higher installation cost within the expected life of the system.
- You don’t pay for COP! (you pay for kilowatt
- hours) The annual savings in heating energy between two heat pumps with different seasonal average COPs can be estimated using this formula: S = load 1 COPL − 1 COPH Where: S = savings in seasonal heating energy (MMBtu*) load = total annual heating energy required for the building (MMBtu*) COPL = seasonal average COP of heat pump having the lower of the two COPs COPH = seasonal average COP of heat pump having the higher of the two COPs * 1 MMBtu = 1,000,000 Btu Example: A house has a design heating load of 36,000 Btu/hr when the outdoor temperature is 0 ºF, and the indoor temperature is 70 ºF. The house is located in Syracuse, NY with 6,720 annual heating ºF
- days. The estimated annual space heating energy use is 49.7 MMBtu. Assume that one heat pump option has a seasonal average COP of 3.28. The other heat pump has a seasonal COP of 2.8.
S = load 1 COPL − 1 COPH 49.7 1 2.8 − 1 3.28 2.6MMBtu / year The cost savings associated with an energy savings of 2.6 MMBtu/hr depends on the cost of electricity. For example, if electricity sells at a flat rate of $0.13 / KWHR, the cost savings would be: Cost savings = 2.6MMBtu year 292.997KWHR 1MMBtu $0.13 KWHR $99 / year Can the added cost of the higher COP heat pump be recovered in a reasonable time?
Example house: 36,000 BTU/hr design load at 70ºF inside & 0 ºF outside Location: Syracuse, NY (6720 heating degree days) Total estimated heating energy required: 49.7 MMBTU / season Average cost of electricity: $0.13/kwhr Distribution system: radiant panels with design load supply temperature = 110ºF AIR-TO-WATER HEAT PUMP OPTION Based on simulation software, a nominal 4.5 ton split system air-to-water heat pump supplying this load has a seasonal COP = 2.8.
Estimated installed cost = $10,600 (not including distribution system) GEOTHERMAL WATER-TO-WATER HEAT PUMP OPTION: Based on simulation using simulation software, a nominal 3 ton water to water heat pump supplying this load from a vertical earth loop has a seasonal COP = 3.28.
Estimated installed cost = $11,800 (earth loop) + $8750 (balance of system) = $20,550 (not including distribution system) Deduct for 30% federal tax credit - 6165) Net installed cost: $14,385 (not including distribution system) Annual space heating cost: AIR-TO-WATER HEAT PUMP (COPave= 2.8) = $676 / yr GEOTHERMAL HEAT PUMP (COPave = 3.28) = $577 / yr Difference in annual heating cost: $99 / year Difference in net installed cost: $3,785 Simple payback on higher cost of geothermal HP: 3785 / 99 ≈ 38 years Diminishing returns of higher COPs Without subsidies the estimated difference in installed cost is $9,950 With reinstated 30% federal tax credit the difference in installed cost is $3785 Initial difference in annual heating cost: $98 / year Draw your own conclusions...
5. Air-to-water heat pumps are significantly less disruptive to install compared to geothermal heat pumps: Several trends suggest that a growing market will emerge for air-to-water heat pumps. www.thegeoecchange.org In my area, vertical earth loops cost about $3,000+ per ton for drilling, pipe insertion, and grouting. Additional cost is incurred for connecting multiple vertical piping loops, and routing piping back to the location of the heat pump. The drill “tailings” usually have to be removed from the site.
Replacement of any affected pavements or landscaping also needs to be factored into the cost of installing a geothermal heat pump system.
Horizontal earth loops require large land areas and major excavation.
6. As home space heating loads get smaller, the domestic water heating load becomes an increasingly higher percentage of the total annual heating energy requirement. A standard electric water heater providing domestic water heating in a situation where the heat pump can not, delivers heat at a COP of 1.0. If that energy was instead attained through an air-to-water heat pump, it could be delivered at a COP averaging perhaps 2.5 over the year. For a family of 4, needing 60 gallons per day of water heated from 50 to 120 ºF, and assuming electrical energy priced at $0.12 per KWHR, the difference in annual domestic water heating cost between these scenarios is $270.
Water heating COP = 2.5+ Water heating COP = 1.0 Several trends suggest that a growing market will emerge for air-to-water heat pumps. Some estimates put the DHW load at 25-30 percent of the total annual energy requirement in a well insulated modern home. Most ductless mini-split heat pumps cannot provide domestic water heating, but a properly configured air-towater heat pump can.
7. The high COP cited for some geothermal heat pumps doesn’t include the power required to move flow through the earth loop. Example: A specific water-to-water geothermal heat pump has the follow listed performance information: Earth loop entering temperature = 30ºF Entering load water temperature = 100 ºF Flow rate (both evaporator and condenser) = 9 gpm Heating capacity = 27,700 Btu/hr Electrical power input = 2370 watts Several trends suggest that a growing market will emerge for air-to-water heat pumps.
Example of a commercially available earth loop flow center. 4, UP26-150 circulators (370 watts each) = 1,480 watts pumping power input.
Based on a typical earth loop, the pumping requirement is 10.5 gpm at 35.5 feet of head. This equates to an estimated pump input of 287 watts. COPHP only = 27700 Btu hr 2.37kw ( ) 3413 Btu hr kw 3.42 The high flow and head required in some geothermal earth loops requires substantial circulator power. COPHP +loop pump = 27700 Btu hr 2.37kw + 0.287kw ( ) 3413 Btu hr kw 3.05 Nominal 11% drop in “net” COP The ANSI 13256-2 standard for geo heat pump COP includes an estimate for the power required to move flow through the heat pump - BUT DOESN’T INCLUDE ANY ALLOWANCE FOR THE EARTH LOOP PUMPING POWER.
Other (unique) air-to-water heat pumps
Split system air-to-water heat pump INDOOR UNIT compressor refrigerant-to-water heat exchanger reversing valve controls desuperheater (for DHW) OUTDOOR UNIT (major components) air-to-refrigerant heat exchanger fan Nordic air-to-water heat pump
Bring your own condenser... ThermAtlantic Energy Products, Inc.
manifold valve actuators zoned radiant ! ceiling panels zone! thermostats buffer tank air source heat pump! outdoor unit ON OFF OFF ON ON! (supplemental)! ON controls electric! boiler DX2W module closed open open absorbed! (low temperature)! heat temperature sensor chilled water air handler Bring your own condenser...
Heating mode Heat pump routes heat to buffer tank Heat delivered from buffer tank to low temperature load
(cooling mode operation) buffer tank air source heat pump! outdoor unit OFF ON ON ON ON electric! boiler ON controls DX2W module mixed partially! open partially! open rejected! heat manifold valve actuators zoned radiant ! ceiling panels zone! thermostats chilled water air handler Bring your own condenser... Cooling mode Heat pump chills buffer tank Chilled water delivered to air handler for latent cooling, & mixing chilled water to radiant panels for sensible cooling
Heating capacity Increases with: a. warmer outdoor temperature b.
lower load water temperature COP Increases with: a. warmer outdoor temperature b. lower load water temperature Heating performance: 20000 40000 60000 80000 -5 5 15 25 35 45 55 65 75 heat output (Btu/hr) outdoor temperature (ºF) 95 ºF 131 ºF leaving water temperature 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 -5 5 15 25 35 45 55 65 75 COP outdoor temperature (ºF) 95 ºF 131 ºF leaving water temperature (inverter drive scroll compressor unit)
Heating performance: Anything that reduces the “temperature lift” increases both the heating capacity and COP of the heat pump. outside air load water temperature! "lift"! (less is better) HEATING MODE OUTSIDE INSIDE outside air load water Low temperature distribution systems are critical to good performance.
Cooling capacity Increases with: a. lower outdoor temperature b. Higher chilled water temperature EER Increases with: a. lower outdoor temperature b. higher chilled water temperature 40000 45000 50000 55000 60000 65000 70000 60 65 70 75 80 85 90 95 100 105 Cooling capacity (Btu/hr) Oudoor air temperature (ºF) leaving chilled water temp = 59 ºF Daikin Alterma model ERLQ054BAVJU leaving chilled water temp = 55 ºF leaving chilled water temp = 50 ºF leaving chilled water temp = 45 ºF 6 7 8 9 10 11 12 13 14 60 65 70 75 80 85 90 95 100 105 Energy Efficiency Ratio (EER) (Btu/hr/watt) Outdoor air temperatue (ºF) leaving chilled water temp = 59 ºF Daikin Alterma model ERLQ054BAVJU leaving chilled water temp = 55 ºF leaving chilled water temp = 50 ºF leaving chilled water temp = 45 ºF Cooling performance:
Anything that decreases the temperature lift’ increases both the cooling capacity and EER of the heat pump. outside air temperature! "lift"! (less is better) chilled water COOLING MODE chilled water outside air OUTSIDE INSIDE Cooling performance: Warmer chilled water temperatures improve performance.
LOW-AMBIENT Air-to-Water Heat Pump Systems
EVI refrigeration cycle evaporator fan outside! air outside! air EVI enabled! compressor condensor (main) TXV! thermal expansion valve refrigerant! "sub-cooler" vapor injection port sub cooled! liquid refrigerant electronic expansion valve water in water out EVI allows increased refrigerant mass flow into evaporator, & at lower entering temperatures.
solenoid valve Standard refrigeration cycle water in evaporator fan outside! air outside! air ! compressor condensor (main) TXV! thermal expansion valve water out
Freeze protection OUTSIDE INSIDE air-to-water heat pump remainder of system fill / purge valves expansion tank air separator pressure relief valve flexible connectors entire system filled with antifreeze solution Simplest option: Use antifreeze solution in entire system
Heat exchangers between heat pump and distribution system IF a heat exchanger is required between heat pump and storage (due to requirement to keep heat pump part of a closed loop), that heat exchanger should be sized for a maximum approach temperature difference of 5 ºF.
February 2015 Upstate NY -23 ºF air temperature -29 ºF wind chill My own installation...
Feb 7, 2018
Design objectives: 1. Be able to serve as heat source for building with 18,000 Btu/hr design load (via radiant floor heating). 2. Retain oil-fired boiler and allow simple manual selection of heat source. (flip of switch) 3. Provide zoned chilled water cooling for 1st floor office, and 2nd floor guest room. 4. Be equipped for BTU metering of energy from heat pump & KWHR meter of electrical energy to heat pump (to calculated COP, and EER)
Supporting the heat pump Treated lumber pedestal to keep unit above snow level Added 2 threaded rods w/ base flanges to stiffen pedestal
Piping details to keep condensate out of wall framing 1” Chamflex hoses with offset to allow small movement 1” FPT copper adapter 2” PVC sleeve wrap with electrical tape for tight fit foam sealant inside
high wall fan coil 1/2” FPT to propex adapter 1/2” MPT lines on air handler end of condensate drain hose condensate drain direct through outside wall 5000 10000 15000 20000 25000 70 80 90 100 110 120 130 140 150 160 Heat ouput (Btu/hr) Entering water temperature (ºF) HW-18-ECM (@ 2.1 gpm flowrate)
Importance of low temperature distribution systems
Heat sources such as condensing boilers, geothermal & ATW heat pumps, and solar collectors all benefit from low water temperature operation. 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 60 80 100 120 140 160 180 200 thermal efficiency (decimal %) inlet fluid temperature (ºF) ambient air temp. = 30ºF! solar radiation = 250 Btu/hr/ft2) 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 100 105 110 115 120 125 Coefficient Of Performance (COP) Entering water temperature (ºF)
FUTURE PROOF” your hydronic systems... Select heat emitters, and design hydronic distribution systems so that they can supply design load output using supply water temperatures no higher than 120 ºF.
Even lower design load supply temperatures are preferred when possible. This is especially important when renewable energy heat sources are used.
- Water temperature ranges for various hydronic heat emitters 80 90 100 110 120 130 140 150 160 170 180 190 200 floor heating (bare slab) wall heating ceiling heating panel radiators fan-coils traditional fin-tube baseboard traditional cast-iron radiators covered heated slab thin slab underfloor tube&plate above floor tube&plate NOT RECOMMENDED 120 ºF, suggested maximum supply water temperature for modern systems
- Don’t feel constrained to select heat emitters based on traditional supply water temperatures...
- The heat output of any heat emitter always drops with decreasing water temperature.
- There is always a trade off between the total surface area of the heat emitters in the system, and the supply water temperature required to meet the heating load.
- More heat emitter area always lowers the required supply water temperature.
- There is always some output provided the supply water temperature is above the room air temperature.
Slab-on-grade floor heating 20 40 60 0 10 20 30 40 50 60 70 80 90 100 upward heat flux! (Btu/hr/ft2) Driving ∆T (Tw-Tr) (ºF)! Average water temp. - room air temp 6-inch tube spacing 12-inch tube spacing Rff=0 Rff=0.5 Rff=1.0 Rff=1.5 Rff=2.0 Rff = resistance of finish flooring (ºF/hr/ft^2/Btu) 4" concrete slab tube spacing
Don’t do this with ANY hydronic heat source! Heat transfer between the water and the upper floor surface is severely restricted!
Heat transfer between the water and the upper floor surface is severely restricted! Don’t do this with ANY hydronic heat source!
Most CONVENTIONAL fin-tube baseboard has been sized around boiler temperatures of 160 to 200 ºF. Much too high for good thermal performance of low temperature hydronic heat sources. Could add fin-tube length based on lower water temperatures. BUT... Fin-tube output at 120 ºF is only about 30% of its output at 200ºF Hydronic heat emitters options for low energy use houses
Some lowtemperature baseboard is now available Hydronic heat emitters options for low energy use houses
One of the fastest responding hydronic heat emitters From setback to almost steady state in 4 minutes...
Panel Radiators Hydronic heat emitters options for low energy use houses
- Panel Radiators Hydronic heat emitters options for low energy use houses As an approximation, a panel radiator operating with an average water temperature of 110 ºF in a room room maintained at 68 ºF, provides approximately 27 percent of the heat output it yields at an average water temperature of 180 ºF.
- Adjust heat output for operation at lower water temperatures.
The “NEO”, just released from Runtal North America Fan-assisted Panel Radiators 8 tube high x 31.5” wide produces 2095 Btu/hr at average water temperature of 104 ºF in 68ºF room 8 tube high x 59” wide produces 5732 Btu/hr at average water temperature of 104 ºF in 68ºF room
Site built radiant CEILINGS... Thermal image of radiant ceiling in operation Where: Q = heat output of ceiling (Btu/hr/ft2) Twater = average water temperature in panel (ºF) Troom = room air temperature (ºF) Heat output formula: q = 0.71× (Twater −Troom )
Site built radiant WALLS...
- completely out of sight
- low mass -fast response
- reasonable output at low water temperatures
- stronger than conventional drywall over studs
- don’t block with furniture q = 0.8 × (Twater −Troom ) Where: Q = heat output of wall (Btu/hr/ft2) Twater = average water temperature in panel (ºF) Troom = room air temperature (ºF) Heat output formula: Site built radiant WALLS...
OUTSIDE INSIDE flexible connectors entire system filled with antifreeze solution (P1) (MV1) (SPC) (HP) Solstice Extreme air-to-water heat pump SPACEPAK (T1) (ZP1) (T2) (ZP2) (S2) point-of-use instantaneous water heater DHW ASSE 1070 valve CW reverse indirect water heater / buffer tank (S1) Reverse indirect tank buffers space heating & significantly preheats domestic water Source: Turbomax tanks
240 VAC 60 amp circuit instantaneous water heater L1 N 120 VAC / 15amp circuit main switch (MS) (S1) sensor 1718 Solstice Extreme heat pump L2 L1 240/120 VAC 30 amp circuit N (HP) L N 15 16 heat pump disconnect switch (HPDS) (P1) (MV1) G (MZRC) (T1) (ZP1) (T2) (ZP2) R C (SPC) DESCRIPTION OF OPERATION: Power supply: The Solstice heat pump, circulator (P1), and motorized valve (MV1) are powered by a dedicated 240/120 VAC 30 amp circuit.
The heat pump disconnect switch (HPDS) must be closed to provide power. The remainder of the control system is powered by 120 VAC 15 amp circuit. The main switch (MS) must be closed to provide power. The instantaneous water heater is supplied by a dedicated 240 VAC / 60 amp circuit.
Heat pump operation: Whenever the main switch (MS) is closed 120 VAC is passed to the multi-zone relay center (MZRC). The (MZRC) passes 24 VAC to the temperature setpoint controller (SPC) which monitor the temperature at sensor (S1) in the buffer tank. If the temperature at sensor (S1) is below 105 ºF, the (SPC) closes its contact, which completes a circuit between terminals 15 and 16 in the Solstice Extreme heat pump, enabling it to operate in heating mode. After a short time delay, circulator (P1) and motorized valve (MV1) will be supplied with 120 VAC from the heat pump. This establishes flow of the system’s antifreeze solution through the heat pump.
The heat pump verifies adequate flow using its internal flow switch, and when adequate flow is proven, starts the heat pump in heating mode. The 120 VAC supplied to (MV1) opens the valve allowing flow between the heat pump and the headers of the thermal storage tank. The system continues in this mode until the temperature at sensor (S1) reaches 125ºF, at which point the contacts in the setpoint controller (SPC) open turning off the heat pump, circulator (P1) and motorized valve (MV1). Space heating: Whenever the main switch (MS) is closed, 24 VAC is sent to thermostats (T1, T2). When either thermostat calls for heating its associated zone circulator (ZP1, ZP2) is turned on.
Domestic water heating: Domestic water passes through the copper tubing coils suspended in the buffer tank. The tank temperature at sensor (S1) is maintained between 105 and 125 ºF. Domestic water passing through the coil will be preheated (or at time fully heated) as it passes through this coil. Any additional temperature rise of the domestic water is provided by the tankless electric water heater. OUTSIDE INSIDE flexible connectors entire system filled with antifreeze solution (P1) (MV1) (SPC) (HP) Solstice Extreme air-to-water heat pump SPACEPAK (T1) (ZP1) (T2) (ZP2) (S2) point-of-use instantaneous water heater DHW ASSE 1070 valve CW reverse indirect water heater / buffer tank (S1) Reverse indirect tank buffers space heating & significantly preheats domestic water
- OUTSIDE INSIDE flexible connectors entire system filled with propylene glycol antifreeze solution (P1) (HP) Solstice Extreme air-to-water heat pump SPACEPAK heated buffer tank temperature sensors (S1) (P2) (SPC) (ORC) (S2) (S3) HEATING MODE All piping and components conveying chilled water must be insulated and vapor sealed (AH1) (ZVH1) (ZVC1) OFF (AH2) (ZVH2) (ZVC2) OFF radiant panel mainfold station 1 radiant panel mainfold station 2 OFF OFF outdoor temperature sensor spring check valve Cold climate air-to-water heat pump system
- Direct-to-load supply side piping
- 80 gallon buffer tank
- 2 zones of radiant panel heating
- 2 zones of chilled water cooling
- High efficiency variable speed distribution circulator
- (AH1) (ZVH1) (ZVC1) OFF (AH2) (ZVH2) (ZVC2) OFF OUTSIDE INSIDE flexible connectors entire system filled with propylene glycol antifreeze solution (P1) (HP) Solstice Extreme air-to-water heat pump SPACEPAK heated buffer tank temperature sensors (S1) (P2) (SPC) (ORC) (S2) (S3) COOLING MODE All piping and components conveying chilled water must be insulated and vapor sealed spring check valve Cold climate air-to-water heat pump
- Direct-to-load supply side piping
- 80 gallon buffer tank
- 2 zones of radiant panel heating
- 2 zones of chilled water cooling
- High efficiency variable speed distribution circulator
L2 L1 240 VAC 15 amp circuit G 1718 Solstice Extreme heat pump L N 15 16 L2 L1 240/120 VAC 30 amp circuit N heat pump disconnect switch (HPDS) (P1) (R2-3) G L2 L1 24 VAC transformer 120/24 VAC (P2) Mode selection switch heat cool off (MSS) R C (ORC) R C (SPC) (S3) sensor (S1) sensors L1 N 120 VAC / 15amp circuit main switch (MS) G (R1-2) R G L1 L2 G (AH2) service switch RC RH W Y G thermostat (T1) (ZVH1) M M (ZVC1) RC RH W Y G thermostat (T2) (ZVH2) M M (ZVC2) (R1) (R2) (R1-1) R G L1 L2 G (AH1) service switch (R2-1) (R2-2) (RC) (RC-1) (RC-2) (S2) Description of operation: Power supply: The Solstice Extreme heat pump and circulator (P1) are powered by a dedicated 240/120 VAC 30 amp circuit.
The heat pump disconnect switch (HPDS) must be closed to provide power to the heat pump. The remainder of the control system is powered by 120 VAC / 15 amp circuit. The main switch (MS) must be closed to provide power to the control system. Both fan coils are powered by a dedicated 120 VAC / 15 amp circuit. The service switch for each air handler must be closed for that air handler to operate. Heating mode: The mode selection switch (MSS) must be set for heating. This passes 24 VAC to the RH terminal in each thermostat. Whenever either thermostat demands heat, 24VAC is passed from the thermostat’s W terminal to the associated zone valve (ZVH1, or ZVH2).
When the zone valve reaches its fully open position its internal end switch closes, passing 24 VAC to relay coil (R1). Relay contact (R1-1) closes to pass 120 VAC to circulator (P2). Relay contact (R1-2) closes to pass 24VAC to outdoor reset controller (ODR). The (ODR) measures outdoor temperature at sensor (S2), and uses this temperature along with it settings to calculate the target supply water temperature for the buffer tank. It then measures the temperature of the buffer tank at sensor (S1). If the temperature at (S1) is more than 3 ºF below the target temperature the (ODR) closes its relay contact.
This completes a circuit between terminals 15 and 16 in the Solstice extreme heat pump, enabling it in heating mode. After a short time delay the heat pump (HP) turns on circulator (P1) and verifies adequate flow through the heat pump. After a short time delay the heat pump compressor turns on it compressor. The heat pump continues to operate until the temperature at sensor (S1) is 3 ºF above the target temperature calculated by the (ODR), or neither thermostat calls for heat, or the heat pump reaches it internal high limit setting. Note: Neither air handler operates in heating mode, regardless of the fan switch setting on the thermostats.
Cooling mode: The mode selection switch (MSS) must be set for cooling. This passes 24VAC to relay coil (RC). normally open contacts (RC-1) and (RC-2) close allowing 24VAC from the air handlers to pass to the RC terminal in each thermostat. Whenever either thermostat calls for cooling, 24VAC is passed from the thermostat’s Y terminal to the associated zone valve (ZVC1, or ZVC2). When the zone valve reaches its fully open position its internal end switch closes, passing 24 VAC to relay coil (R2). Relay contact (R2-1) closes to pass 120 VAC to circulator (P2). Relay contact (R2-2) closes to pass 24VAC to the cooling setpoint controller (SPC).
The cooling setpoint controller measures the temperature of the buffer tank at sensor (S3). If this temperature is 60 ºF or higher, the (SPC) relay contact closes completing a circuit between terminals 15 and 16 on the Solstice Extreme heat pump (HP) enabling it to operate. Relay contact (R2-3) closes between terminals 17 and 18 in the Solstice Extreme heat pump (HP), switching it to cooling mode. The heat pump (HP) turns on circulator (P1) and verifies adequate flow through the heat pump. After a short time delay the heat pump compressor turns on it compressor and operates in chiller mode.
This continues until the temperature at sensor (S3) drops to 45 ºF, or until neither zone thermostat calls for cooling, or until the heat pump reaches in internal low limit setting. The blowers in the air handlers can be manually turned on at the thermostats when the mode selection switch (MSS) is set to cooling. The blowers will operate automatically whenever either cooling zone is active. Cold climate air-to-water heat pump system
- The mod/con boiler can serve as a “peaking tool” to meet peak loads when necessary.
- The heat pump can be smaller in capacity relative to design load. This is helpful in applications where the cooling load is significantly smaller than the design heating load.
- Having a mod/con boiler as a secondary heat source provides full or partial backup if the heat pump is not operating.
- The boiler’s electrical power demand is relatively small compared to the heat pump. This makes it more feasible to operate the heating system from a modestly-sized backup generator during power outages.
- In areas where time-of-use electrical rates are available, it would be possible to operate the heat pump when off-peak rates are in effect, and avoid high on-peak rates by using the boiler as the heat source. Dynamic Duo: hydronic heat pump + boiler
- zoned space heating
- single zone cooling
- domestic hot water
- automatic aux boiler Heating + Cooling +DHW (HX) OUTSIDE INSIDE spring-loaded check valves DHW single zone air handler for cooling buffer tank diverter valve mod/con boiler (P3) (P4) air vent PEX, or PEX-AL-PEX tubing dual isolation valve thermostatic operator TRV towel warmer radiator air vent manifold station variable speed circulator (P2) (S1) temp. sensor 2-stage temperature setpoint controller (SPH) (FS1) AB A B (DV1) (AH1) P&T isolation and flushing valves for potable side of HX N.O. N.C. (S2) (P1) Solstice SE air to water heat pump Entire system filled with propylene glycol antifreeze solution. Single thermal mass tank 2 stage or inverter drive heat pump very important to avoid short cycling in cooling mode.
Electrical Wiring Heating + Cooling +DHW (HX) OUTSIDE INSIDE spring-loaded check valves DHW single zone air handler for cooling buffer tank diverter valve mod/con boiler (P3) (P4) air vent PEX, or PEX-AL-PEX tubing dual isolation valve thermostatic operator TRV towel warmer radiator air vent manifold station variable speed circulator (P2) (S1) temp. sensor 2-stage temperature setpoint controller (SPH) (FS1) AB A B (DV1) (AH1) P&T isolation and flushing valves for potable side of HX N.O. N.C. (S2) (P1) Solstice SE air to water heat pump L1 N 120 VAC main switch (MS) 24 VAC transformer 120/24 VAC (RH2-1) (P2) 2-stage setpoint controller (P3) R C (SPH) (RH1) sensor (S1) (Rdhw) (FS1) (Rdhw-1) (P4) Mode selection switch (RH2) T T mod/con boiler R C sensor (S2) master thermostat RC RH W Y G (RB-1) (AH1) (RB) off heat cool off cool (SPC) (B1) (T1) (MSS) (DV1) L2 L1 240 VAC N (P1) (HP) L N (RH1-1) (RH1-2) stage 1 stage 2 43 44 5 6 Solstice SE heat pump
Heating + Cooling +DHW Description of Operation Please read this later in the PDF Heat Source Operation: When the main switch (MS) is closed, power is available to the line voltage and low voltage portions of the electrical system. 24VAC is applied to power up the 2-stage setpoint controller (SPH). This controller (SPH) measures the temperature at sensor (S1) in the upper portion of the thermal storage tank. If that temperature is below the user-set stage1 setpoint (in this case 125 ºF), minus half the user-set differential (in this case half the differential is 5 ºF), then the stage 1 contacts in (SPH) close.
For space heating operation, the (DPDT) mode selection switch must be set to heat. This passes 24VAC to the RH terminal of the master thermostat (T1). It also allows 24 VAC to pass from the stage 1 contacts in the (SPH) controller to energize the diverter valve (DV1) and relay coil (RH1). Relay contact (RH1-1) closes between terminal 43 and 44 on the Solstice SE heat pump turning it on in the heating mode. Relay contact (RH1-2) opens between terminals 5 and 6 on the Solstice SE heat pump allowing it to operate in heating mode. An internal relay within the heat pump turns on circulator (P1).
Heat from the heat pump flows to the upper header of the buffer tank. The heat pump and these associated devices continue to operate as described until sensor (S1)in the buffer tank climbs to a temperature of 130 ºF, or if the master thermostat (T1) stops calling for heat.
If, during a call for space heating from master thermostat (T1), the temperature at sensor (S1) in the upper portion of the buffer tank drops to 115 ºF, the stage 2 contacts in the setpoint controller (SPH) will close. These contacts complete a low voltage circuit powered through the boiler, and enable the boiler to operate in a fixed upper temperature mode. The boiler turns on circulator (P3) through an internal relay. The boiler continues to operate until the buffer tank sensor (S1) reaches a temperature of (130 ºF), at which point the boiler turns off, and so does circulator (P3). Note: The boiler will operate in this mode regardless of whether the mode selection switch is set to heat or cool.
This allows the boiler to maintain a suitable temperature in the buffer tank for domestic water heating even when the heat pump is operating as a chiller.
Space Heating Distribution: When master thermostat (T1) calls for heat, 24VAC passes from its W terminal to energize the coil of relay (RH2). Contact (RH2-1) closes to pass 120 VAC to circulator (P2). This circulator is set to operate in constant differential pressure mode to provide the necessary flow to any panel radiator that does not have its thermostatic valve fully closed. Circulator (P2) will automatically vary its speed to maintain approximately constant differential pressure across the manifold station serving the panel radiators. The thermostatic valves on each radiator can be used to limit heat input as desired.
Domestic Water Heating Mode: Whenever there is a demand for domestic hot water of 0.6 gpm or more, flow switch (FS1) closes. This passes 24VAC to energize the coil of relay (Rdhw). Contact (Rdhw-1) closes to pass 120 VAC to circulator (P4). Heated antifreeze solution flows from the upper portion of the buffer tank will flow through the primary side of heat exchanger (HX), and transfer heat to the cold domestic water flow through the secondary side of the heat exchanger (HX). When the demand for domestic hot water drops to 0.4 gpm or less, flow switch (FS1) opens. This turns off relay (Rdhw) and circulator (P4).
All domestic hot water leaving the system passes through a thermostatic mixing valve to limit the water temperature to the distribution system. Cooling Mode: For cooling operation the mode selection switch (MSS) must be set to cool. This passes 24 VAC to the RC terminal of the master thermostat. If the master thermostat is set for cooling operation, and calls for cooling, 24VAC is passed to its Y terminal. From the Y terminal, 24VAC passes to energize the coil of relay (RB). A normally open set of contacts (RB-1) close to pass 120 VAC to the air handler (AH1) turning it on. 24VAC also passes from the Y terminal of the master thermostat to energize cooling setpoint controller (SPC).
Once energized, (SPC) monitors the temperature of sensor (S2) on the inlet pipe to the air handler. If that temperature is above 60 ºF the contacts in (SPC) close. This completes a circuit between terminals 43 and 44 in the Solstice SE heat pump, turning it on in cooling mode. The heat pump turns on circulator (P1) through its internal relay. All necessary devices for cooling operation are now active. The system remains in cooling operation until either the cooling demand is removed at thermostat (T1), or the temperature at sensor (S2) on the air handler inlet drops to 40 ºF, at which point the heat pump, circulator (P1), and air handler (AH1) turn off.
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