IBM Research - Zurich
GmbH
Saeumerstrasse 4
8803 Rueschlikon
Switzerland
Authors:
email:
Date:
Version:
Fabian Mueller
Olle Sundstroem
Dieter Gantenbein
{fmu,osu,dga}@zurich.ibm.com
04.09.2014
3.1
Subject:
IBM EcoGrid Direct-Price Agent Implementation Status
1
1
Scope
This document specifices the IBM EcoGrid Direct-Price Agent v3.0 behavior, as an
enhancement over the versions 1.0 and 2.1 used in the 2013/14 heating season [1][2].
The new version 3.1 of the price agent aims at increasing the demand-response potential
without sacrificing any customer comfort. As introduced in this document, it distinguishes
between heat pump installations and direct electric heating installations. Moreover, it
redefines the construction of the upper and lower temperature bounds based on the userset reference temperature and the chosen flexibility level, as well as many timing
parameters.
Version 3.1 includes a specification for delivering demand response even in situations
where indoor temperature is unavailable1 (defined as a measurement that is more than 4h
old).
1
Version 3.0 did not include this feature
2
2
Definitions of temperature bands
The user specifies a reference temperature Tr in the GWR UI, see Figure 1 left screenshot
(native Danish language version used on Bornholm). Optionally, the user may also specify
individual comfort priority and flexibility level, see Figure 1 right screenshot:
Figure 1 GWR UI user settings: The user can decide whether or not to allow automation “Tillad styring”, and
define individual comfort priorities “Individuelle indstillinger”, and modify the reference temperature “Afbryd
styring under” (stop control below this temp). Comfort priority settings comprise the day time priority
“Prioriter” {Morning, Daytime, Evening} as well as the desired flexibility level “Profil” {Low, Medium, High}.
They become active on Save “Gem”.
The user-set flexibility levels {Low, Medium, High} translate into a temperature range
Tflex(t) that determines the allowed temperature above the reference temperature Tr. The
mapping from flexibility level to temperature range also depends on the comfort priority
setting and, thus, can vary over time. In case the user does not select individual settings,
cf. left screenshot in Figure 1, a default temperature range is set that is valid for the entire
day; it corresponds to the “otherwise” in Table 1 which also provides detailed information
about how flexibility and comfort priority settings are translated to allowed temperature
ranges, for all comfort priority settings.
Flexibility Tflex(t) [°C]
Comfort priority
Morning
Daytime
Evening
06:00-10:00
otherwise
08:00-18:00
otherwise
17:00-23:00
otherwise
3
3
3
3
3
3
2
Medium 3
4
High
2
4
2
3
2
4
2
3
2
4
6
4
6
4
6
Default
Low
Table 1 Flexible temperature range Tflex(t) [°C] for different levels of flexibility and comfort priorities. These values
apply to both heat pump and electric heating installations. In case the user does not specify individual settings, the
default values “otherwise” are applied.
In addition to the user settings, the temperature set point for the heating devices’ internal
thermostat control Tth must be set such that Tth>=Tr+max{Tflex(t)}. This lower bound on Tth is
required to guarantee that the heating devices will turn on whenever they are enabled by the
3
IBM price agent. However, Tth should be chosen such that this temperature is acceptable in
the worst case, see Section 5 for more details.
4
3
Heat Pump Model and Constraints
The version of the direct-price agent described in this document uses a very simple heat pump
model. It is assumed that the heat pump consumes a constant amount of power PON when in
operation, and a constant amount of power POFF when idle. The numeric power level values can
be identified for every house individually. Table 2 provides a set of typical values.
Heat Pump Operation State
ON
OFF
Constant Power
Consumption
4000W
130W
Table 2 Example of heat pump power levels.
The heat pump runtime constraints used in the new price agent version 3.1 are provided in Table
2 for different flexibility levels. In contrast to previous versions of the direct-price agent, the
maximum total off-time is now specified for 24 hours. In addition, if indoor temperature is
unavailable Table 2 shows that version 3.1 still provides flexibility.
User-set Flexibility
Level
Minimum
Off-time
Maximum
Off-time
Minimum
On-time
Max. total Off-time per 24h
Temperature
available (<4h)
Temperature
unavailable (>4h)
Low
Medium
High
30min
30min
30min
30min
60min
90min
120min
90min
60min
180min (12.5%)
360min (25%)
720min (50%)
30min (2.1%)
60min (4.2%)
120min (8.3%)
Table 3 Heat pump (HP) operational constraints for different user settings.
4
Direct Electric Heating Model and Constraints
The model used for direct electric heating is similar to the heat pump model introduced above. It
also assumes constant power consumption if the device is ON. If it is OFF, no power is
consumed at all.
Electric Heating Operation State
Constant Power Consumption
ON
OFF
4000W
0W
Table 4 Example of electric heating power levels.
The electric heating runtime constraints used in the new price agent version 3.1 are provided in
Table 5 for different flexibility levels. The dynamics of an electric heater are assumed to be very
fast. Thus, only short minimum ON/OFF times are considered. . In addition, if indoor
temperature is unavailable Table 5 shows that version 3.1 still provides flexibility.
User-set Flexibility
Level
Minimum
Off-time
Maximum
Off-time
Minimum
On-time
Max. total Off-time per 24h
Temperature
available (<4h)
Temperature
unavailable (>4h)
Low
Medium
High
5min
5min
5min
10min
15min
20min
5min
5min
5min
180min (12.5%)
360min (25%)
720min (50%)
30min (2.1%)
60min (4.2%)
120min (8.3%)
Table 5 Direct electrical heating (EH) operational constraints for different user settings.
5
5
Behavior of Price Agent
This section describes the behavior of the new price agent v3.1. There are 3 different
behavioral modes depending on the current temperature T(t), the thermostat set point Tth,
and the user settings. Note that this feature is only active if indoor temperature T(t)
measurements are available, i.e., less than 4h old.
1.
T
he temperature is below the reference temperature (T(t)<Tr):
In this case, the heating devices are constantly enabled.
2.
T
he temperature is within the flexible temperature range
(Tr<=T(t)<=Tr+Tflex(t)): In this temperature range, the heating
devices are enabled or disabled with the goal of minimizing energy
costs based on the EcoGrid real-time prices. All the operational
constraints as defined in Tables 3 and 5 are considered.
3.
T
he temperature is above the allowed temperature range (T(t)>
Tr+Tflex(t)): In this case, the automation switches to the flexibility
level `High’ that allows for maximal OFF-times to correct over
temperatures, but still under the operational constraints of High as
defined in Tables 3 and 5.
Disclaimer: Note that it is possible for the temperature to go below Tr or exceed Tr+Tflex(t).
Even when the agent will switch to behavior (3) in above list and run the automation with a
flexibility level `High’, decreasing of the temperature may not always succeed. The actual
house indoor temperature depends on many external factors. Examples include: open doors
and windows, the current weather situation, solar irradiation through windows, the thermal
characteristics of the house, and also on potentially other active but uncontrolled heating
devices.
6
Figure 2 Definition of different temperature bands. The minimum required temperature Tr is set by the user in the
GUI. If the actual temperature drops below this value, the heating devices are enabled constantly. The upper
temperature limit is given by adding the flexible temperature range Tflex(t) to Tr. If the temperature exceeds this
value, the heating devices are controlled with high flexibility with the aim of bringing the temperature below Tth
again. A large thermostat set point temperature Tth, where Tth>=Tr+max{Tflex(t)}, is required for the devices to start
heating whenever they are enabled by the IBM price-agent.
6
Energy-Procurement Cost Minimization
Given a price forecast for a fixed planning horizon, the IBM direct-price agent version 3.1
computes a heating device enablement schedule that (i) minimizes the total energyprocurement cost accumulated over the planning horizon based on the EcoGrid real-time
price and that (ii) simultaneously satisfies all operational constraints as specified in Tables 3
and 5 depending on the device type.
7
Security Features
In addition to the operational constraints discussed in Sections 3 and 4, the following security
features are implemented to guarantee pilot participant freedom and best-possible efforts to
establish an indoor air temperature higher or equal to the user-set minimum comfort
temperature at all times.
As soon as at least one of the following conditions is true, any planned minimum
procurement-cost enablement schedule will be pre-empted and the heat pump is
unconditionally enabled to operate according to its native parameters.
i.
ii.
iii.
iv.
The indoor air temperature as measured by the GreenWave temperature sensor
is below the user-set minimum temperature Tr.
The communication between server and GreenWave gateway in house is lost
for more than 30 minutes (in this case the automatic scene will be executed).
Oestkraft or the participant operationally bail out the household from
automation by unchecking the optimize flag in the GreenWave user interface.
The IBM-agent administrative automation state for the household is set to
disabled (example as done over Christmas Holiday Season 2013/14).
7
References
[1]
Mueller, F., Sundstroem, O., Gantenbein, D. (2013). IBM EcoGrid Direct-Price Agent
Implementation Status v.1.0. IBM Research Zurich.
[2]
BIBLIOGRAPHY \l 1033 Mueller, F., Sundstroem, O., Gantenbein, D. (2014). IBM
EcoGrid Direct-Price Agent
Implementation Status v2.1. IBM Research Zurich.
[3]
Mueller, F., Sundstroem, O., Gantenbein, D. (2014). IBM EcoGrid Direct-Price Agent
Implementation Status v3.0. IBM Research Zurich.
8