Double Heat Sinks

Double Heat Sinks, often abbreviated DHS and colloquially also referred to as Freezers throughout the Inner Sphere after their NAIS codename, operate in much the same way and for the same purpose as standard heat sinks. The difference is that a double heat sink offers twice the heat dissipation capacity of a standard heat sink, for the same mass (one ton).

Their drawback is that they are much bulkier than a standard heat sink (unless integrated into a fusion engine). The advanced Clan version is twice the size of a standard heat sink; Star League era double heat sinks and those later (re-)developed by the Inner Sphere are three times as bulky as a standard heat sink.

Also, double heat sinks are normally incompatible with standard heat sinks. A given unit must therefore be equipped exclusively with either standard or double heat sinks, though exceptions are known.

The benefits of doubled heat dissipation capacity usually outweigh the drawbacks and by 3058 almost every 'Mech model was equipped or retrofitted with double heat sinks. In general, the lighter 'Mechs have trouble making use of all available pod space, making the bulk issue meaningless. The heaviest mechs are less limited by tonnage and more limited by pod space. That said, the benefits of "free" double heat sinks in the engine usually outweighs that tradeoff anyway.

History
Introduced as a prototype in 2567 by the Terran Hegemony. Prototype versions of this heat sink functioned as normal, except designers hadn't figured out how to place the double heat sink inside the engine the same as standard heat sinks could be placed. This resulted in some "hybrid sinks" (single sinks in the fusion engine, double sinks used on the hull) being used on some 'Mechs until the production variant was released, with double sinks being included with applicable fusion engines. Double heat sinks were commonly available during the Star League era but became Lostech over the course of the Succession Wars. Although the technology was essentially extinct after 2865 and standard (single) heat sinks became the norm as they were the only ones still available, double heat sinks remained in use in some individual cases.

By the early 31st century, double heat sink technology was on the verge of rediscovery. The Federated Suns had a double heat sink project in its prototype stages by 3022 with individual samples built into operative BattleMechs, and in 3030, towards the end of the Fourth Succession War, the Capellan Confederation already fielded their BJ-3 Blackjack variant, the first regular 'Mech design sporting double heat sinks in decades if not centuries. (Although it is not generally known, the Confederation did not develop double heat sinks themselves; the Federated Suns had prototypes manufactured in the Lyran Commonwealth and a Capellan agent was able to siphon a share of the production off to the Confederation. )

Following the discovery of the Helm Memory Core and the subsequent dissemination of lost Star League knowledge throughout the Inner Sphere in 3028, double heat sinks gradually became a staple of 'Mech construction again and were extensively used in retrofits and new designs. The NAIS had double heat sinks ready for serial production in 3041.

Models
The Double Heat Sink is manufactured on the following planets:

Non-standard subtypes
Besides the normal Star League era double heat sinks used throughout the Inner Sphere and the advanced Clan version, a number of experimental or prototype technologies existed at various times with slightly different capabilities. However, it should be noted that none of these proved viable for mass production or deployment.

Prototype Double Heat Sinks
The prototype Double Heat Sinks developed in the closing years of the Age of War and in the period between the discovery of the Helm Memory Core and the reintroduction of the standard Double Heat Sink shared almost identical characteristics with each other. Functionally, these prototypes were identical to standard Double Heat Sinks, with the following exceptions: firstly, prototype Double Heat Sinks couldn't be mounted in engines. Secondly, the prototype Double Heat Sinks in use in the mid-Thirty-first century could be combined with single heat sinks when used in BattleMechs, while the prototype Double Heat Sinks in use during the Reunification War could be combined with single heat sinks in any combat unit that could mount double heat sinks.

Double-Strength Heat Sinks
Relying on corrosive liquid metal coolants instead of advanced radiators for efficiency, Double-Strength Heat Sinks were developed by the Federated Suns near the end of the Third Succession War at the Friden Aerospace Park research installation on Hoff as part of Project Phoenix. Unlike regular double heat sinks, they could be combined with standard heat sinks at leisure and were actually used as refit kits, replacing individual regular heat sinks. In this, they were plainly superior to regular double heat sinks, sharing none of their drawbacks. (It remains unclear whether or not they could be mounted in the engine). However, they were too brittle and hard to maintain for more than a few years' worth of function.

When the Draconis Combine invaded Hoff in 3022, some 'Mechs among the defenders were equipped with functional prototypes of this type but they are believed to have been destroyed in the fighting. As far as can be determined, neither the Federated Suns nor the Draconis Combine ever used these exact same Double-Strength Heat Sinks again after the battles on Hoff.

Following the sacking of their facility at Hoff, the Federated Suns found they lacked the industrial capacity to resume production of the prototypes. They approached various Lyran Commonwealth firms to build components which were brought together at Hesperus II where Kincaid Defiance Industries assembled them and secretly shipped them to New Avalon from ca. 3026 onwards. The Capellan Confederation obtained a share of these prototypes through an agent.

Corrosive Coolant Experimental Double Heat Sinks
In the late 3030s, the nascent Federated Commonwealth deployed another kind of experimental double heat sinks with corrosive liquid metal coolants. Obviously developed from the prototypes deployed on Hoff, they could also be combined with regular heat sinks but could not be mounted in the engine, and were three times as big (although still had the same mass). Like their predecessors, maintenance problems meant they decayed within only a few years and were unsuitable for widespread deployment, although they did give the Federated Commonwealth a brief advantage in its early days.

Fanmade rebalancing
Many BattleTech players have objected to the introduction of Double Heat Sinks, even to the point of saying they "ruin the game". Indeed, though double heat sinks "seem" to have a cost, in practice Fusion Engines come with 10 internal Heat Sinks that can be turned into Double Heat Sinks at nil cost to slot or tonnage. In turn this upgrades immensely the use of Energy Weapons and makes the already bad AutoCannons even worse.

But, what if Double Heat Sinks were actually balanced? Let's look at some options...

No internal Double Heat Sinks
Simple: Let's say that Double Heat Sinks were only ever designed for external, not inside-engine use.  All engine Heat Sinks are Single Heat Sinks. Heat sink mode only affects external ones. Mechs can still be used as before. The "problem" is some of them will overheat much more often (example, Clan energy-based 'Mechs such as the Mad Cat/Timberwolf). Additional Battle Value of DHS will have to be halved for balance.

An alternate wording:  All Double Heat Sinks are Prototype Double Heat Sinks. Heat sink mode only affects external ones. The difference in this wording compared to the previous one is that it would allow combination of external double and single heat sinks in the same unit, as it was with 31st century prototype DHS.

Double Heat Sink Internal Expansion
Another partial nerf, but not a so heavy one as the previous one. It is incompatible with the former rule.  With this rule, double heat sinks inside engines take double "in-engine" space, including default ones. Thus, Fusion engines will only fit five Double Heat Sinks by default. The base dissipation is still 10 instead of 20, but 5 tons are freed. The disadvantage to this rule is that it's a "back to the drawing board" with every double heatsink using design since they will have free tonnage (and still less dissipation).