March 15, 2011 Daikin Altherma/Viessmann Integration Notes (used with schematics M1 thru M5) Our Daikin Altherma project involves integrating an indoor unit (EKHBX054BA3VJU) with an existing domestic hot water, high temperature radiant panel, and low temperature radiant floor heating system. The existing system is built around a Viessmann Vitola 200 propane fired boiler, a Vitotronic 200 control system, a Divicon mixing station, and a Vitocell 300 domestic hot water tank. The Divicon serves 6 radiant zones; each zone has a thermostat that controls its respective circulator through a Taco circulator control. There is one zone of high temperature radiant wall panels served by a high temperature circulator. Both high temp and mixed temp boiler circuits utilize heating curves reset using outside temperature. The Vitocell 300 tank is served by a domestic hot water circulator. This existing system is approximately 6 years old and represents what once was the state of the art in hydronic heating. Overall system efficiency is on the order of 80 to 90%. Until recently, there was no realistic or cost effective way to significantly reduce system operating costs or improve upon this level of energy efficiency. We see the arrival of the Altherma in the United States as a tremendous opportunity to rectify this situation. Our perception is that owners of Viessmann hydronic systems are typically willing to invest in an efficient heating system and are very interested in energy efficiency and are therefore ideal candidates for an Altherma retrofit project. The purpose of the notes that follow is to outline our approach to the integration of the Altherma with the Viessmann system what the pre-existing system looks like, different approaches to integrating the two heat sources, and determining the optimum use of the Altherma s capabilities. Pre-existing Viessmann System: Schematic M1 (left illustration) The existing boiler has a domestic hot water (dhw) circuit, a high temperature circuit, and a mixed temperature circuit. The domestic hot water circuit uses the factory default schedule that enables operation from 5:30 AM to 10:30 PM every day. Whenever dhw tank temp falls below the dhw setpoint (currently 130F) the boiler temp rises to 180 F and the dhw circulator operates. The high temp circuit is a single zone of radiant wall panels served by a high temp circuit circulator controlled by a Taco switching relay and zone thermostat. The high temp circuit
operates on the factory default schedule that enables boiler operation from 6 AM to 10 PM every day. Based on an outside reset curve with a high temp of 180 F at 0 F outside, the boiler maintains the appropriate reset temp at all times of enabled operation. As this high temp circuit is used infrequently, there are quite a few hours of unnecessary propane consumption to maintain boiler standby temperature. The mixed temp circuit has constant circulation provided by the built in circulator in the Divicon mixing station. Connected to this mix temp circuit are six radiant zone circulators controlled by a Taco circulator control from zone thermostats. The returns from the six zones (some in concrete floors and some in wood floors) feed back into the mix temp circuit right after the last radiant zone supply. Use of large diameter tubing in the mix temp circuit (resulting in negligible pressure drop) and the pressure gradient from the Divicon mixing circulator help to ensure that system pressures are fairly uniform and that the zone and mixing circulators work well with each other. Based on an outside reset curve with a mix temp of 120 F at 0 F outside, the boiler maintains the appropriate reset temp at all times of enabled operation. As the high temp circuit reset curve is always hotter than necessary for the radiant zones, the Divicon mixing station is constantly mixing radiant loop return water with boiler supply to reduce the radiant supply temperature. Altherma Integration With Viessmann: Schematic M1: (right illustrations) Parallel versus Series: We feel that installing the Altherma in series with the Viessmann presents several advantages over alternating or parallel installations. Installation instructions for the Altherma indicate in Application 5 the use of either a boiler or the hydrobox as a source for a hydronic system. If return temperatures of the system can be held below 120 F, we feel that there are several advantages to operating the two sources in series and simultaneously: Maximize Heat Output from Altherma with the Coldest Return Water: If the Altherma hydrobox and Viessmann boiler are in series then we can ensure that the coldest return water will go to Altherma first resulting in the greatest opportunity to extract heat from the hydrobox (if return temperature is too high, the hydrobox will reach a point where it can no longer heat the hydronic flow through the heat exchanger). Maximize Heat Output from Altherma as First Stage: Given a fixed hydronic input temp, the hydrobox output temp will rise and fall with the capacity of the heat pump as a function of outside temperature. As the hydrobox output temp drops the Viessmann Divicon mixing station will add hot water to bring the supply temp up to the reset setpoint. Having the hydrobox first in a series arrangement will automatically ensure that the Altherma will always have the opportunity to add as much heat as possible to the hydronic flow.
Increased Heat Pump Annual Run Time: If the hydrobox and boiler are installed in parallel, we feel that the instantaneous burner/divicon mixing station output of the boiler would be much greater than the output of the hydrobox. Mix temp circuit target temperature would be achieved quickly and the overall runtime of the heat pump would be reduced. A series installation may reduce instantaneous heat input to the mix temp circuit but will increase Altherma run time as stage 1 to almost 100% or continuous operation during the coldest parts of the heating seaon. Our perception is that operation of the Altherma is more economical than operation of the Viessmann boiler as the Altherma annual operating hours increase, the annual operating cost of the entire system will decrease. Altherma/Viessmann Integration: (Schematic M1 inset, upper right illustration and Schematic M2) The return flow from the mixed temp circuit goes to a 40 gallon buffer tank (necessary to ensure adequate hydronic system volume) and into the inlet of the hydrobox. The Daikin motorized 3 way valve directs hydrobox output to either the Daikin domestic hot water tank or the heating system. (Application 3) The heating output from the Daikin 3 way valve goes to a motorized 3 way valve (labeled RadMV1) that directs flow either directly to the radiant system or through the Viessmann Divicon mixing station. In the Altherma only heating mode, hydronic flow bypasses the Divicon mixing station and circulates through the mixed temp circuit. Operation of the Altherma is controlled by the normally open end switch of the Taco circulator control (as room thermostat ) that operates the radiant zone circulators. Target temperature for the hydronic flow is determined by the reset curve calculated by the Altherma user interface. In the Altherma Viessmann series heating mode, motorized valve RadMV1 connects the Altherma hydrobox output to the Viessmann Divicon mixing station inlet and the Divicon circulator starts. (Though the motorized valve has a 90 second actuator we feel that the addition of the Viessmann circulator to the Altherma circulator will ensure that flow will be sufficient for the hydrobox throughout the valve travel). The Divicon mixing station will add boiler hot water as necessary to the Altherma input to raise the supply temperature to the mix temp circuit reset setpoint. Due to the ample size of the mix temp circuit the additional flow from both hydrobox and Divicon circulators operating in series (with additive pump head) should not create interaction problems with the existing radiant zone circulators. Both hydrobox and Divicon circulators will be on together during the periods of highest building heat loss when more radiant zone circulators will be operating. During periods of lower building heat loss, only the hydrobox circulator will be operating.
Buffer Tank Connection Choices: (Schematic M1, right illustrations) There are several ways to connect the heat sources (Altherma hydrobox and Viessmann boiler) to the mix temp circuit that serves the radiant zones. A buffer tank is used to ensure that the hydronic system volume is adequate for hydrobox operation. A buffer tank can also be used to isolate system circulators and reduce undesired flow issues by creating a region of common pressure. This approach requires a somewhat different control strategy with consequent benefits and drawbacks. Buffer tank in series: (Schematic M1 inset, upper right illustration and Schematic M2): In this approach, the buffer tank is in series with the Altherma and Viessmann circulators. The radiant zone thermostats activate the zone circulators via a Taco circulator control. The normally open end switch of the Taco control calls the Altherma directly (as a room thermostat ) and the user interface activates the Altherma hydrobox circulator. This hydrobox circulator runs in addition to any radiant zone circulator anytime there is a radiant call. This will somewhat increase annual hydrobox circulator run time but the ability of the Altherma to modulate hydronic output saves energy (compared to a typical on/off American heat pump). Temperature control is also improved as there is very little system lag between the radiant zone call and heat pump operation. When temperature outside drops below Radiant Stat setting and the Taco end switch is calling, the Viessmann is brought in as the second stage. This arrangement runs the Viessmann Divicon mixing circulator in series with the Altherma hydrobox circulator. As the Divicon mixing station is fully modulating and fairly fast acting, temperature control is not affected and there is little system lag introduced by starting the second stage. Due to the ample size of the mix temp circuit piping the operation of the radiant zone circulators should not be affected by the operation of the Altherma and Viessmann circulators. Buffer tank hydraulically separating: (Schematic M1 inset, lower right illustration) In this approach, the buffer tank serves as a hydraulic isolator between the radiant zone circulators and the Altherma and Viessmann circulators. The supply and return sides of the radiant zones are separated (note the connection is removed in the illustration). This arrangement would permit the operation of the radiant zone circulators independently of the Altherma and Viessmann circulators. We use this connection approach with non-modulating heat sources (typical American on/off heat pumps) that have one heat output level. A buffer tank decouples the heat output level of the heat pump from the heat input level going to a radiant zone and reduces short cycling of the heat source. It can also reduce annual circulator energy use by permitting radiant zone circulators to remove heat from the buffer tank without always running the heat source circulator.
The buffer tank temperature would drive operation of the Altherma and Viessmann sources. One possibility would be to use a Tekmar 264 staging control to look at buffer tank temp the 264 would take the radiant zone Taco end switch input and operate the Altherma as a first stage and the Viessmann as a second stage. It would use the radiant supply manifold input temp as a control input. Typically, a buffer tank installed this way permits multiple circulators of different sizes to peacefully coexist and lets non-modulating heat sources cycle more efficiently independent of small heating loads. This approach usually experiences an increased lag in system response (buffer tank and radiant zone temperatures vary to a greater degree) and increased cost of system controls when compared to a modulating system (as with the buffer tank in series as depicted in the upper illustration). Domestic Hot Water System: (Schematic M2: (upper inset)) A Daikin domestic hot water tank is connected to the Altherma hydrobox via the Daikin 3 way motorized valve. An existing Viessmann domestic hot water tank is connected to the boiler via a dedicated dhw circulator. A DHW Stat is used to select a changeover point between Altherma and Viessmann production of domestic hot water (initial setting of 40 F outside). Below this setting, we wish to dedicate all of the heat pump output to space heating through the radiant zones. The Viessmann boiler will be responsible for the entire dhw load. Above an initial setting of 40 F, we wish to disable Viessmann dhw production and have the Altherma continue with both space heating and dhw production. A motorized 3 way valving arrangement switches between the preheat and final dhw tank; below the initial setting of 40 F, the Daikin dhw tank is preheat and the Viessmann is final above 40 F their roles reverse. As the climate of Martha s Vineyard experiences great temperature swings in the transitional seasons, this switching arrangement ensures that any energy spent heating domestic hot water is not lost as the outside temperature rises above and falls below the 40 F setpoint. From a sanitary perspective, this arrangement also ensures that both tanks are always filled with potable water fit for human consumption. Building and DHW Loads: Schematic M3 The upper illustration is a depiction of the building heat loss as a function of outside temperature (at a maximum at 0 F outside down to a minimum at 68 F warm weather shutdown). Plotted against this is the heating output of the Altherma as a function of outside temperature (blue shaded area). There will be a balance temperature above which the Altherma output will be able to meet the entire building heat loss. Below this balance temperature, the Viessmann boiler output will be added as a second stage (orange shaded area) to meet the increasing building heat loss.
The Vitotronic control on the Viessmann has two outside reset temperature curves that serve the high temp and mix temp circuits. An additional Viessmann control, the Switching Module V, permits the external control of the boiler burner. Below the initial setting of 40 F outside, the Radiant Stat enables the burner and the boiler will maintain the high temp reset curve. While this is somewhat inefficient, it is the Viessmann approach so that the boiler is ready if there is a call from the high temp circuit radiant panel zone. Above the initial setting of 40 F, the Radiant Stat will disable the boiler burner and the building heat loss will be met by the Altherma output. The lower illustration is a depiction of domestic hot water production by either the Viessmann boiler or the Daikin Altherma. The orange shaded rectangle indicates the temperature range in which the Viessmann boiler will perform dhw heating; the blue rectangle represents Altherma dhw heating. On the y axis we show hourly domestic hot water output the Viessmann hourly output of dhw will be somewhat greater than the Altherma output. We expect that due to projected use, the Altherma dhw output will be entirely satisfactory. Below an initial setting of 40 F, the DHW Stat will enable boiler burner operation and switch the motorized valves so that the Daikin dhw tank serves as preheat to the Viessmann tank. The Vitotronic control will sense tank temperature and operate the burner and dhw circulator to maintain 130 F in the Viessmann tank. The Altherma output will be devoted to space heating and domestic hot water production will be disabled via a field setting. Above 40 F, the DHW Stat will switch dhw roles by changing the motorized valve positions and disabling the Viessmann boiler burner. The Viessmann dhw tank will now serve as preheat and the Daikin dhw tank will maintain 125 F. Smart Grid Integration: The project location is also part of a SmartGrid integration project with General Electric and the Vineyard Energy Project, a local energy group. We are serving as their technical liaison with the 50 families in the pilot project. Real time information about current electricity pricing (3 price tiers) will be available at a local GE interface device and can be used as an input to the Altherma. We wish to use this kwh pricing information and the benefit rate kwh power supply field settings on the Altherma to determine backup and booster heater operation. A comparison can be made between the price of propane (at a projected system efficiency of 90% for the Viessmann installation) versus the current electricity price tier (at a projected COP of 1 for the booster and backup heater).
Control Details: Schematics M4 and M5 This schematic shows one approach to the controls necessary to integrate the Daikin Altherma with the existing Viessmann system. As described above, the external interface to the Viessmann system will be their Switching Module V which permits remote control of the boiler burner. When the contact X7 on this module is closed, burner operation is disabled. Therefore, the domestic hot water, radiant, and hi temp relays all have their burner disable contacts in series. Any one of these relays may call for burner operation independently of each other. Domestic Hot Water Controls: Schematics M4 and M5 A DHW Stat responds to a drop in outside temperature below the initial setpoint of 40 F and closes an internal contact which powers the DHW Relay. (For the sake of simplicity we depict this DHW Stat as a Honeywell remote bulb controller T675A1508 with adjustable differential and operating range of 0 F to 100 F. We expect that this switching function can easily be provided by a web based DDC system that we hope to use to trend system operation.) When powered, the DHW Relay will power the motorized valves DHWMV1, DHWMV2, and DHWMV3 to their Daikin dhw preheat/viessmann dhw final position. The DHW Relay will also close the circulator contact and connect the Viessmann dhw circulator to the Vitotronic 200 on the boiler. The normally closed contacts on the burner disable points will open and enable burner operation. The Vitotronic control on the boiler will monitor Viessmann dhw tank temperature and will now be able to heat domestic hot water as necessary. Similarly, when the DHW Stat experiences a rise in outside temperature above the initial setpoint (plus the adjustable differential) of 40 F, the internal contacts will open and the DHW Relay will return to its unpowered state. The DHW Relay will then power the motorized valves DHWMV1, DHWMV2, and DHWMV3 to their Viessmann dhw preheat/ Daikin dhw final position. The DHW Relay will also open the circulator contact and disconnect the Viessmann dhw circulator from the Vitotronic 200 on the boiler. The burner disable points will return to their normally closed position. The field settings on the Altherma hydrobox will ensure that domestic hot water is now generated by the heat pump system. Radiant Heating Controls: Schematics M4 and M5 A Radiant Stat responds to a drop in outside temperature below the initial setpoint of 40 F and closes its internal contacts. Local radiant zone thermostats connected to a Taco circulator control operate their respective radiant zone circulators and close a normally open end switch on the Taco
control. This end switch and the Radiant Stat contacts are in series; if both contacts are made then the Radiant Relay is powered. (As with the DHW Stat we depict the Radiant Stat as a Honeywell remote bulb controller T675A1508 with adjustable differential and operating range of 0 F to 100 F. We expect that this switching function can easily be provided by a web based DDC system that we hope to use to trend system operation.) When powered, the Radiant Relay will power the motorized valve RadMV1 to direct hydronic flow from the Altherma hydrobox outlet to the Viessmann Divicon mixing station inlet. The Radiant Relay will also close the circulator contact and connect the Divicon mix circulator to the Vitotronic 200 on the boiler. The normally closed contacts on the burner disable points will open and enable burner operation. The Vitotronic control on the boiler will monitor Viessmann boiler and will heat the boiler to the high temp reset curve (only because this reset curve is always hotter than the mix temp reset curve). Similarly, when the Radiant Stat experiences a rise in outside temperature above the initial setpoint (plus the adjustable differential) of 40 F or all of the radiant zone thermostats are satisfied and the Taco end switch opens, the Radiant Relay will return to its unpowered state. The Radiant Relay will then power the motorized valve RadMV1 to direct hydronic flow to bypass the Viessmann Divicon mixing station. In this mode, only the Altherma hydrobox output will be connected to the mix temp circuit and the radiant zones. The Radiant Relay will also open the circulator contact and disconnect the Viessmann Divicon mix circulator from the Vitotronic 200 on the boiler. The burner disable points will return to their normally closed position. Hi Temp Heating Controls: Schematics M4 and M5 The hi temp thermostat connected to a Taco switching relay circulator control operates the hi temp zone circulator and closes a normally open end switch on the Taco control. When this end switch closes the Hi Temp Relay is powered. When the Hi Temp Relay is powered, the normally closed contacts on the burner disable points will open and enable burner operation. The Vitotronic control on the boiler will monitor Viessmann boiler temp and will heat the boiler to the high temp reset curve. When the hi temp thermostat is satisfied and the Taco end switch opens, the Hi Temp Relay will return to its unpowered state. The burner disable points will return to their normally closed position.