From db29d172f51f95c2cc9fa52b8042d2863599d91e Mon Sep 17 00:00:00 2001
From: mwerezak <mwerezak@gmail.com>
Date: Fri, 11 Jul 2014 14:34:07 -0400
Subject: [PATCH] Air alarm cooling now resembles thermodynamics

Gas cooling power consumption now resembles the work required to operate
a Carnot heat pump. Cooling hot air takes less energy than cooling cold
air.
---
 code/ZAS/_gas_mixture.dm     | 24 ++++++++++++++++++++++++
 code/game/machinery/alarm.dm | 31 +++++++++++++++++++------------
 2 files changed, 43 insertions(+), 12 deletions(-)

diff --git a/code/ZAS/_gas_mixture.dm b/code/ZAS/_gas_mixture.dm
index 2a072e8ef9c..749fc4d9a81 100644
--- a/code/ZAS/_gas_mixture.dm
+++ b/code/ZAS/_gas_mixture.dm
@@ -141,6 +141,30 @@ What are the archived variables for?
 
 	return max(MINIMUM_HEAT_CAPACITY,heat_capacity_archived)
 
+//this seems like such a common thing to do I can't believe this hasn't been made into it's own proc yet.
+/datum/gas_mixture/proc/add_thermal_energy(var/thermal_energy)
+	//Purpose: Adjusting temperature based on thermal energy transfer
+	//Called by: Anyone who wants to add or remove energy from the gas mix
+	//Inputs: An amount of energy in J to be added. Negative values remove energy.
+	//Outputs: The actual thermal energy change.
+	
+	var/old_temperature = temperature
+	var/heat_capacity = heat_capacity()
+	
+	temperature += thermal_energy/heat_capacity
+	if (temperature < 0)
+		temperature = 0
+	
+	return (temperature - old_temperature)*heat_capacity
+
+/datum/gas_mixture/proc/get_thermal_energy_change(var/new_temperature)
+	//Purpose: Determining how much thermal energy is required
+	//Called by: Anyone. Machines that want to adjust the temperature of a gas mix.
+	//Inputs: None
+	//Outputs: The amount of energy required to get to the new temperature in J. A negative value means that energy needs to be removed.
+	
+	return heat_capacity()*(new_temperature - temperature)
+
 /datum/gas_mixture/proc/total_moles()
 	return total_moles
 	/*var/moles = oxygen + carbon_dioxide + nitrogen + phoron
diff --git a/code/game/machinery/alarm.dm b/code/game/machinery/alarm.dm
index ad70d7ca010..aee79735556 100644
--- a/code/game/machinery/alarm.dm
+++ b/code/game/machinery/alarm.dm
@@ -198,18 +198,25 @@
 		var/datum/gas_mixture/gas
 		gas = location.remove_air(0.25*environment.total_moles)
 		if(gas)
-			var/heat_capacity = gas.heat_capacity()
-			var/energy_used = min( abs( heat_capacity*(gas.temperature - target_temperature) ), MAX_ENERGY_CHANGE)
-
-			//Use power.  Assuming that each power unit represents 1 watts....
-			use_power(energy_used, ENVIRON)
-
-			//We need to cool ourselves.
-			if(environment.temperature > target_temperature)
-				gas.temperature -= energy_used/heat_capacity
-			else
-				gas.temperature += energy_used/heat_capacity
-
+			
+			if (gas.temperature <= target_temperature)	//gas heating
+				var/energy_used = min( gas.get_thermal_energy_change(target_temperature) , MAX_ENERGY_CHANGE)
+				
+				gas.add_thermal_energy(energy_used)
+				use_power(energy_used, ENVIRON)
+			else	//gas cooling
+				var/heat_transfer = min(abs(gas.get_thermal_energy_change(target_temperature)), MAX_ENERGY_CHANGE)
+				
+				//Assume the heat is being pumped into the hull which is fixed at 20 C
+				//none of this is really proper thermodynamics but whatever
+				
+				//heat transfer is limited by the max amount of power the heat pump can put out, which lets say is also MAX_ENERGY_CHANGE
+				heat_transfer = min(heat_transfer, gas.temperature/T20C*MAX_ENERGY_CHANGE)
+				var/energy_used = heat_transfer * T20C/gas.temperature
+				
+				gas.add_thermal_energy(-heat_transfer)
+				use_power(energy_used * 1.1, ENVIRON)	//heat pump inefficiencies
+			
 			environment.merge(gas)
 
 			if(abs(environment.temperature - target_temperature) <= 0.5)