Equithermic regulation

Equithermic regulation is a simple method of calculating the temperature of heating or cooling medium in primary circuit depending on the outdoor temperature. In most cases, this function is managed internally by boiler or heat pump.

If the shape of the curve is set correctly, it should be possible to achieve desired temperature in zones with coolest possible medium (in heating mode) or warmest possible medium (in cooling mode).

Disadvantage of this method is, that it does not have automatic correction mechanism built-in. So if the equithermic curve is not set correctly, it may result in insufficient or excessive heating / cooling in zones.

	Heating mode	Cooling mode
Inputs	Outdoor temperature Temperatures from zones	Outdoor temperature Temperatures from zones Humidity from zones
Output	Set point of virtual thermostat for primary circuit	Set point of virtual thermostat for primary circuit
Limits	Minimum / Maximum set point	Minimum / Maximum set point Dew point limit (Early warning) Calculates minimal set point temperature based on highest relative humidity from all linked zone thermostats
PID correction	(X)	(X)

For more information about cooling / heating modes, see this page.

How final set point is calculated

Equitherm curve returns temperature of flow water based on outdoor temperature. Angle of the curve, parallel shift, temperature limits and adjustments based on data from thermostats are affecting the final results.

Angle

For floor heating systems, values between 0.2 and 0.8 are commonly used. Lower values are more suitable for high quality insulation.

Table below shows resulting set point temperature based on outdoor temperature and angle of the curve:

Outdoor temperature
Angle:	-20ºC	-15ºC	-10ºC	-5ºC	0ºC	5ºC	10ºC	15ºC	20ºC
0.2	33	32	32	30	29	27	24	22	20
0.4	42	40	38	36	33	30	27	24	20
0.6	50	48	45	41	37	33	29	25	20
0.8	59	56	52	47	42	37	31	26	20
1.0	65	61	57	53	47	40	34	27	20
1.2	74	69	64	58	52	44	37	28	20
1.5	82	76	70	64	58	50	40	30	20
1.75	90	84	77	71	63	54	43	32	20
2.0	90	90	84	77	70	60	47	34	20
2.25	90	90	88	82	75	65	52	36	20
2.5	90	90	90	87	80	70	56	38	20
2.75	90	90	90	90	84	73	57	38	20
3.0	90	90	90	90	86	77	61	41	20

E.g. if outdoor temperature is 0ºC and angle of equithermic curve is 0.6, resulting set point temperature is 37ºC.

Parallel shift

Increases or decreases the curve by defined value.

E.g. if set point temperature based on angle of curve is 37ºC, and parallel shift is set to 4ºC, resulting set point is 41ºC.

Adjustments based on data from thermostats

All zone termostats that are linked to equithermic Smart Rule are affecting the final result.

	Heating mode	Cooling mode
Set point from zones	Equithermic curve will be shifted up if highest set point of zone thermostats is more than 22ºC	Equithermic curve will be shifted down if lowest set point of zone thermostats is less than 22ºC
Result	Resulting set point = Set point based on angle and parallel shift + Ratio * (highest zone setpoint - 22)	Resulting set point = Set point based on angle and parallel shift + Ratio * (lowest zone setpoint - 22)
Dew point limit	--	Resulting set point can not be less than dew point temperature calculated from highest relative humidity in zones

Equithermic regulation

How final set point is calculated

Angle

Parallel shift

Adjustments based on data from thermostats

Example scenario for zone hydronic heating with equitherm regulation

Example scenario for zone hydronic cooling with equitherm regulation